xref: /freebsd-11.0-release/contrib/gcc/doc/extend.texi

@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1996, 1998, 1999, 2000,
@c 2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.

@c This is part of the GCC manual.
@c For copying conditions, see the file gcc.texi.

@node C Extensions
@chapter Extensions to the C Language Family
@cindex extensions, C language
@cindex C language extensions

@opindex pedantic
GNU C provides several language features not found in ISO standard C@.
(The @option{-pedantic} option directs GCC to print a warning message if
any of these features is used.)  To test for the availability of these
features in conditional compilation, check for a predefined macro
@code{__GNUC__}, which is always defined under GCC@.

These extensions are available in C and Objective-C@.  Most of them are
also available in C++.  @xref{C++ Extensions,,Extensions to the
C++ Language}, for extensions that apply @emph{only} to C++.

Some features that are in ISO C99 but not C89 or C++ are also, as
extensions, accepted by GCC in C89 mode and in C++.

@menu
* Statement Exprs::     Putting statements and declarations inside expressions.
* Local Labels::        Labels local to a block.
* Labels as Values::    Getting pointers to labels, and computed gotos.
* Nested Functions::    As in Algol and Pascal, lexical scoping of functions.
* Constructing Calls::	Dispatching a call to another function.
* Typeof::              @code{typeof}: referring to the type of an expression.
* Conditionals::        Omitting the middle operand of a @samp{?:} expression.
* Long Long::		Double-word integers---@code{long long int}.
* Complex::             Data types for complex numbers.
* Decimal Float::       Decimal Floating Types. 
* Hex Floats::          Hexadecimal floating-point constants.
* Zero Length::         Zero-length arrays.
* Variable Length::     Arrays whose length is computed at run time.
* Empty Structures::    Structures with no members.
* Variadic Macros::	Macros with a variable number of arguments.
* Escaped Newlines::    Slightly looser rules for escaped newlines.
* Subscripting::        Any array can be subscripted, even if not an lvalue.
* Pointer Arith::       Arithmetic on @code{void}-pointers and function pointers.
* Initializers::        Non-constant initializers.
* Compound Literals::   Compound literals give structures, unions
                         or arrays as values.
* Designated Inits::	Labeling elements of initializers.
* Cast to Union::       Casting to union type from any member of the union.
* Case Ranges::		`case 1 ... 9' and such.
* Mixed Declarations::	Mixing declarations and code.
* Function Attributes:: Declaring that functions have no side effects,
                         or that they can never return.
* Attribute Syntax::    Formal syntax for attributes.
* Function Prototypes:: Prototype declarations and old-style definitions.
* C++ Comments::        C++ comments are recognized.
* Dollar Signs::        Dollar sign is allowed in identifiers.
* Character Escapes::   @samp{\e} stands for the character @key{ESC}.
* Variable Attributes::	Specifying attributes of variables.
* Type Attributes::	Specifying attributes of types.
* Alignment::           Inquiring about the alignment of a type or variable.
* Inline::              Defining inline functions (as fast as macros).
* Extended Asm::        Assembler instructions with C expressions as operands.
                         (With them you can define ``built-in'' functions.)
* Constraints::         Constraints for asm operands
* Asm Labels::          Specifying the assembler name to use for a C symbol.
* Explicit Reg Vars::   Defining variables residing in specified registers.
* Alternate Keywords::  @code{__const__}, @code{__asm__}, etc., for header files.
* Incomplete Enums::    @code{enum foo;}, with details to follow.
* Function Names::	Printable strings which are the name of the current
			 function.
* Return Address::      Getting the return or frame address of a function.
* Vector Extensions::   Using vector instructions through built-in functions.
* Offsetof::            Special syntax for implementing @code{offsetof}.
* Atomic Builtins::	Built-in functions for atomic memory access.
* Object Size Checking:: Built-in functions for limited buffer overflow
                        checking.
* Other Builtins::      Other built-in functions.
* Target Builtins::     Built-in functions specific to particular targets.
* Target Format Checks:: Format checks specific to particular targets.
* Pragmas::             Pragmas accepted by GCC.
* Unnamed Fields::      Unnamed struct/union fields within structs/unions.
* Thread-Local::        Per-thread variables.
@end menu

@node Statement Exprs
@section Statements and Declarations in Expressions
@cindex statements inside expressions
@cindex declarations inside expressions
@cindex expressions containing statements
@cindex macros, statements in expressions

@c the above section title wrapped and causes an underfull hbox.. i
@c changed it from "within" to "in". --mew 4feb93
A compound statement enclosed in parentheses may appear as an expression
in GNU C@.  This allows you to use loops, switches, and local variables
within an expression.

Recall that a compound statement is a sequence of statements surrounded
by braces; in this construct, parentheses go around the braces.  For
example:

@smallexample
(@{ int y = foo (); int z;
   if (y > 0) z = y;
   else z = - y;
   z; @})
@end smallexample

@noindent
is a valid (though slightly more complex than necessary) expression
for the absolute value of @code{foo ()}.

The last thing in the compound statement should be an expression
followed by a semicolon; the value of this subexpression serves as the
value of the entire construct.  (If you use some other kind of statement
last within the braces, the construct has type @code{void}, and thus
effectively no value.)

This feature is especially useful in making macro definitions ``safe'' (so
that they evaluate each operand exactly once).  For example, the
``maximum'' function is commonly defined as a macro in standard C as
follows:

@smallexample
#define max(a,b) ((a) > (b) ? (a) : (b))
@end smallexample

@noindent
@cindex side effects, macro argument
But this definition computes either @var{a} or @var{b} twice, with bad
results if the operand has side effects.  In GNU C, if you know the
type of the operands (here taken as @code{int}), you can define
the macro safely as follows:

@smallexample
#define maxint(a,b) \
  (@{int _a = (a), _b = (b); _a > _b ? _a : _b; @})
@end smallexample

Embedded statements are not allowed in constant expressions, such as
the value of an enumeration constant, the width of a bit-field, or
the initial value of a static variable.

If you don't know the type of the operand, you can still do this, but you
must use @code{typeof} (@pxref{Typeof}).

In G++, the result value of a statement expression undergoes array and
function pointer decay, and is returned by value to the enclosing
expression.  For instance, if @code{A} is a class, then

@smallexample
        A a;

        (@{a;@}).Foo ()
@end smallexample

@noindent
will construct a temporary @code{A} object to hold the result of the
statement expression, and that will be used to invoke @code{Foo}.
Therefore the @code{this} pointer observed by @code{Foo} will not be the
address of @code{a}.

Any temporaries created within a statement within a statement expression
will be destroyed at the statement's end.  This makes statement
expressions inside macros slightly different from function calls.  In
the latter case temporaries introduced during argument evaluation will
be destroyed at the end of the statement that includes the function
call.  In the statement expression case they will be destroyed during
the statement expression.  For instance,

@smallexample
#define macro(a)  (@{__typeof__(a) b = (a); b + 3; @})
template<typename T> T function(T a) @{ T b = a; return b + 3; @}

void foo ()
@{
  macro (X ());
  function (X ());
@}
@end smallexample

@noindent
will have different places where temporaries are destroyed.  For the
@code{macro} case, the temporary @code{X} will be destroyed just after
the initialization of @code{b}.  In the @code{function} case that
temporary will be destroyed when the function returns.

These considerations mean that it is probably a bad idea to use
statement-expressions of this form in header files that are designed to
work with C++.  (Note that some versions of the GNU C Library contained
header files using statement-expression that lead to precisely this
bug.)

Jumping into a statement expression with @code{goto} or using a
@code{switch} statement outside the statement expression with a
@code{case} or @code{default} label inside the statement expression is
not permitted.  Jumping into a statement expression with a computed
@code{goto} (@pxref{Labels as Values}) yields undefined behavior.
Jumping out of a statement expression is permitted, but if the
statement expression is part of a larger expression then it is
unspecified which other subexpressions of that expression have been
evaluated except where the language definition requires certain
subexpressions to be evaluated before or after the statement
expression.  In any case, as with a function call the evaluation of a
statement expression is not interleaved with the evaluation of other
parts of the containing expression.  For example,

@smallexample
  foo (), ((@{ bar1 (); goto a; 0; @}) + bar2 ()), baz();
@end smallexample

@noindent
will call @code{foo} and @code{bar1} and will not call @code{baz} but
may or may not call @code{bar2}.  If @code{bar2} is called, it will be
called after @code{foo} and before @code{bar1}

@node Local Labels
@section Locally Declared Labels
@cindex local labels
@cindex macros, local labels

GCC allows you to declare @dfn{local labels} in any nested block
scope.  A local label is just like an ordinary label, but you can
only reference it (with a @code{goto} statement, or by taking its
address) within the block in which it was declared.

A local label declaration looks like this:

@smallexample
__label__ @var{label};
@end smallexample

@noindent
or

@smallexample
__label__ @var{label1}, @var{label2}, /* @r{@dots{}} */;
@end smallexample

Local label declarations must come at the beginning of the block,
before any ordinary declarations or statements.

The label declaration defines the label @emph{name}, but does not define
the label itself.  You must do this in the usual way, with
@code{@var{label}:}, within the statements of the statement expression.

The local label feature is useful for complex macros.  If a macro
contains nested loops, a @code{goto} can be useful for breaking out of
them.  However, an ordinary label whose scope is the whole function
cannot be used: if the macro can be expanded several times in one
function, the label will be multiply defined in that function.  A
local label avoids this problem.  For example:

@smallexample
#define SEARCH(value, array, target)              \
do @{                                              \
  __label__ found;                                \
  typeof (target) _SEARCH_target = (target);      \
  typeof (*(array)) *_SEARCH_array = (array);     \
  int i, j;                                       \
  int value;                                      \
  for (i = 0; i < max; i++)                       \
    for (j = 0; j < max; j++)                     \
      if (_SEARCH_array[i][j] == _SEARCH_target)  \
        @{ (value) = i; goto found; @}              \
  (value) = -1;                                   \
 found:;                                          \
@} while (0)
@end smallexample

This could also be written using a statement-expression:

@smallexample
#define SEARCH(array, target)                     \
(@{                                                \
  __label__ found;                                \
  typeof (target) _SEARCH_target = (target);      \
  typeof (*(array)) *_SEARCH_array = (array);     \
  int i, j;                                       \
  int value;                                      \
  for (i = 0; i < max; i++)                       \
    for (j = 0; j < max; j++)                     \
      if (_SEARCH_array[i][j] == _SEARCH_target)  \
        @{ value = i; goto found; @}                \
  value = -1;                                     \
 found:                                           \
  value;                                          \
@})
@end smallexample

Local label declarations also make the labels they declare visible to
nested functions, if there are any.  @xref{Nested Functions}, for details.

@node Labels as Values
@section Labels as Values
@cindex labels as values
@cindex computed gotos
@cindex goto with computed label
@cindex address of a label

You can get the address of a label defined in the current function
(or a containing function) with the unary operator @samp{&&}.  The
value has type @code{void *}.  This value is a constant and can be used
wherever a constant of that type is valid.  For example:

@smallexample
void *ptr;
/* @r{@dots{}} */
ptr = &&foo;
@end smallexample

To use these values, you need to be able to jump to one.  This is done
with the computed goto statement@footnote{The analogous feature in
Fortran is called an assigned goto, but that name seems inappropriate in
C, where one can do more than simply store label addresses in label
variables.}, @code{goto *@var{exp};}.  For example,

@smallexample
goto *ptr;
@end smallexample

@noindent
Any expression of type @code{void *} is allowed.

One way of using these constants is in initializing a static array that
will serve as a jump table:

@smallexample
static void *array[] = @{ &&foo, &&bar, &&hack @};
@end smallexample

Then you can select a label with indexing, like this:

@smallexample
goto *array[i];
@end smallexample

@noindent
Note that this does not check whether the subscript is in bounds---array
indexing in C never does that.

Such an array of label values serves a purpose much like that of the
@code{switch} statement.  The @code{switch} statement is cleaner, so
use that rather than an array unless the problem does not fit a
@code{switch} statement very well.

Another use of label values is in an interpreter for threaded code.
The labels within the interpreter function can be stored in the
threaded code for super-fast dispatching.

You may not use this mechanism to jump to code in a different function.
If you do that, totally unpredictable things will happen.  The best way to
avoid this is to store the label address only in automatic variables and
never pass it as an argument.

An alternate way to write the above example is

@smallexample
static const int array[] = @{ &&foo - &&foo, &&bar - &&foo,
                             &&hack - &&foo @};
goto *(&&foo + array[i]);
@end smallexample

@noindent
This is more friendly to code living in shared libraries, as it reduces
the number of dynamic relocations that are needed, and by consequence,
allows the data to be read-only.

@node Nested Functions
@section Nested Functions
@cindex nested functions
@cindex downward funargs
@cindex thunks

A @dfn{nested function} is a function defined inside another function.
(Nested functions are not supported for GNU C++.)  The nested function's
name is local to the block where it is defined.  For example, here we
define a nested function named @code{square}, and call it twice:

@smallexample
@group
foo (double a, double b)
@{
  double square (double z) @{ return z * z; @}

  return square (a) + square (b);
@}
@end group
@end smallexample

The nested function can access all the variables of the containing
function that are visible at the point of its definition.  This is
called @dfn{lexical scoping}.  For example, here we show a nested
function which uses an inherited variable named @code{offset}:

@smallexample
@group
bar (int *array, int offset, int size)
@{
  int access (int *array, int index)
    @{ return array[index + offset]; @}
  int i;
  /* @r{@dots{}} */
  for (i = 0; i < size; i++)
    /* @r{@dots{}} */ access (array, i) /* @r{@dots{}} */
@}
@end group
@end smallexample

Nested function definitions are permitted within functions in the places
where variable definitions are allowed; that is, in any block, mixed
with the other declarations and statements in the block.

It is possible to call the nested function from outside the scope of its
name by storing its address or passing the address to another function:

@smallexample
hack (int *array, int size)
@{
  void store (int index, int value)
    @{ array[index] = value; @}

  intermediate (store, size);
@}
@end smallexample

Here, the function @code{intermediate} receives the address of
@code{store} as an argument.  If @code{intermediate} calls @code{store},
the arguments given to @code{store} are used to store into @code{array}.
But this technique works only so long as the containing function
(@code{hack}, in this example) does not exit.

If you try to call the nested function through its address after the
containing function has exited, all hell will break loose.  If you try
to call it after a containing scope level has exited, and if it refers
to some of the variables that are no longer in scope, you may be lucky,
but it's not wise to take the risk.  If, however, the nested function
does not refer to anything that has gone out of scope, you should be
safe.

GCC implements taking the address of a nested function using a technique
called @dfn{trampolines}.  A paper describing them is available as

@noindent
@uref{http://people.debian.org/~aaronl/Usenix88-lexic.pdf}.

A nested function can jump to a label inherited from a containing
function, provided the label was explicitly declared in the containing
function (@pxref{Local Labels}).  Such a jump returns instantly to the
containing function, exiting the nested function which did the
@code{goto} and any intermediate functions as well.  Here is an example:

@smallexample
@group
bar (int *array, int offset, int size)
@{
  __label__ failure;
  int access (int *array, int index)
    @{
      if (index > size)
        goto failure;
      return array[index + offset];
    @}
  int i;
  /* @r{@dots{}} */
  for (i = 0; i < size; i++)
    /* @r{@dots{}} */ access (array, i) /* @r{@dots{}} */
  /* @r{@dots{}} */
  return 0;

 /* @r{Control comes here from @code{access}
    if it detects an error.}  */
 failure:
  return -1;
@}
@end group
@end smallexample

A nested function always has no linkage.  Declaring one with
@code{extern} or @code{static} is erroneous.  If you need to declare the nested function
before its definition, use @code{auto} (which is otherwise meaningless
for function declarations).

@smallexample
bar (int *array, int offset, int size)
@{
  __label__ failure;
  auto int access (int *, int);
  /* @r{@dots{}} */
  int access (int *array, int index)
    @{
      if (index > size)
        goto failure;
      return array[index + offset];
    @}
  /* @r{@dots{}} */
@}
@end smallexample

@node Constructing Calls
@section Constructing Function Calls
@cindex constructing calls
@cindex forwarding calls

Using the built-in functions described below, you can record
the arguments a function received, and call another function
with the same arguments, without knowing the number or types
of the arguments.

You can also record the return value of that function call,
and later return that value, without knowing what data type
the function tried to return (as long as your caller expects
that data type).

However, these built-in functions may interact badly with some
sophisticated features or other extensions of the language.  It
is, therefore, not recommended to use them outside very simple
functions acting as mere forwarders for their arguments.

@deftypefn {Built-in Function} {void *} __builtin_apply_args ()
This built-in function returns a pointer to data
describing how to perform a call with the same arguments as were passed
to the current function.

The function saves the arg pointer register, structure value address,
and all registers that might be used to pass arguments to a function
into a block of memory allocated on the stack.  Then it returns the
address of that block.
@end deftypefn

@deftypefn {Built-in Function} {void *} __builtin_apply (void (*@var{function})(), void *@var{arguments}, size_t @var{size})
This built-in function invokes @var{function}
with a copy of the parameters described by @var{arguments}
and @var{size}.

The value of @var{arguments} should be the value returned by
@code{__builtin_apply_args}.  The argument @var{size} specifies the size
of the stack argument data, in bytes.

This function returns a pointer to data describing
how to return whatever value was returned by @var{function}.  The data
is saved in a block of memory allocated on the stack.

It is not always simple to compute the proper value for @var{size}.  The
value is used by @code{__builtin_apply} to compute the amount of data
that should be pushed on the stack and copied from the incoming argument
area.
@end deftypefn

@deftypefn {Built-in Function} {void} __builtin_return (void *@var{result})
This built-in function returns the value described by @var{result} from
the containing function.  You should specify, for @var{result}, a value
returned by @code{__builtin_apply}.
@end deftypefn

@node Typeof
@section Referring to a Type with @code{typeof}
@findex typeof
@findex sizeof
@cindex macros, types of arguments

Another way to refer to the type of an expression is with @code{typeof}.
The syntax of using of this keyword looks like @code{sizeof}, but the
construct acts semantically like a type name defined with @code{typedef}.

There are two ways of writing the argument to @code{typeof}: with an
expression or with a type.  Here is an example with an expression:

@smallexample
typeof (x[0](1))
@end smallexample

@noindent
This assumes that @code{x} is an array of pointers to functions;
the type described is that of the values of the functions.

Here is an example with a typename as the argument:

@smallexample
typeof (int *)
@end smallexample

@noindent
Here the type described is that of pointers to @code{int}.

If you are writing a header file that must work when included in ISO C
programs, write @code{__typeof__} instead of @code{typeof}.
@xref{Alternate Keywords}.

A @code{typeof}-construct can be used anywhere a typedef name could be
used.  For example, you can use it in a declaration, in a cast, or inside
of @code{sizeof} or @code{typeof}.

@code{typeof} is often useful in conjunction with the
statements-within-expressions feature.  Here is how the two together can
be used to define a safe ``maximum'' macro that operates on any
arithmetic type and evaluates each of its arguments exactly once:

@smallexample
#define max(a,b) \
  (@{ typeof (a) _a = (a); \
      typeof (b) _b = (b); \
    _a > _b ? _a : _b; @})
@end smallexample

@cindex underscores in variables in macros
@cindex @samp{_} in variables in macros
@cindex local variables in macros
@cindex variables, local, in macros
@cindex macros, local variables in

The reason for using names that start with underscores for the local
variables is to avoid conflicts with variable names that occur within the
expressions that are substituted for @code{a} and @code{b}.  Eventually we
hope to design a new form of declaration syntax that allows you to declare
variables whose scopes start only after their initializers; this will be a
more reliable way to prevent such conflicts.

@noindent
Some more examples of the use of @code{typeof}:

@itemize @bullet
@item
This declares @code{y} with the type of what @code{x} points to.

@smallexample
typeof (*x) y;
@end smallexample

@item
This declares @code{y} as an array of such values.

@smallexample
typeof (*x) y[4];
@end smallexample

@item
This declares @code{y} as an array of pointers to characters:

@smallexample
typeof (typeof (char *)[4]) y;
@end smallexample

@noindent
It is equivalent to the following traditional C declaration:

@smallexample
char *y[4];
@end smallexample

To see the meaning of the declaration using @code{typeof}, and why it
might be a useful way to write, rewrite it with these macros:

@smallexample
#define pointer(T)  typeof(T *)
#define array(T, N) typeof(T [N])
@end smallexample

@noindent
Now the declaration can be rewritten this way:

@smallexample
array (pointer (char), 4) y;
@end smallexample

@noindent
Thus, @code{array (pointer (char), 4)} is the type of arrays of 4
pointers to @code{char}.
@end itemize

@emph{Compatibility Note:} In addition to @code{typeof}, GCC 2 supported
a more limited extension which permitted one to write

@smallexample
typedef @var{T} = @var{expr};
@end smallexample

@noindent
with the effect of declaring @var{T} to have the type of the expression
@var{expr}.  This extension does not work with GCC 3 (versions between
3.0 and 3.2 will crash; 3.2.1 and later give an error).  Code which
relies on it should be rewritten to use @code{typeof}:

@smallexample
typedef typeof(@var{expr}) @var{T};
@end smallexample

@noindent
This will work with all versions of GCC@.

@node Conditionals
@section Conditionals with Omitted Operands
@cindex conditional expressions, extensions
@cindex omitted middle-operands
@cindex middle-operands, omitted
@cindex extensions, @code{?:}
@cindex @code{?:} extensions

The middle operand in a conditional expression may be omitted.  Then
if the first operand is nonzero, its value is the value of the conditional
expression.

Therefore, the expression

@smallexample
x ? : y
@end smallexample

@noindent
has the value of @code{x} if that is nonzero; otherwise, the value of
@code{y}.

This example is perfectly equivalent to

@smallexample
x ? x : y
@end smallexample

@cindex side effect in ?:
@cindex ?: side effect
@noindent
In this simple case, the ability to omit the middle operand is not
especially useful.  When it becomes useful is when the first operand does,
or may (if it is a macro argument), contain a side effect.  Then repeating
the operand in the middle would perform the side effect twice.  Omitting
the middle operand uses the value already computed without the undesirable
effects of recomputing it.

@node Long Long
@section Double-Word Integers
@cindex @code{long long} data types
@cindex double-word arithmetic
@cindex multiprecision arithmetic
@cindex @code{LL} integer suffix
@cindex @code{ULL} integer suffix

ISO C99 supports data types for integers that are at least 64 bits wide,
and as an extension GCC supports them in C89 mode and in C++.
Simply write @code{long long int} for a signed integer, or
@code{unsigned long long int} for an unsigned integer.  To make an
integer constant of type @code{long long int}, add the suffix @samp{LL}
to the integer.  To make an integer constant of type @code{unsigned long
long int}, add the suffix @samp{ULL} to the integer.

You can use these types in arithmetic like any other integer types.
Addition, subtraction, and bitwise boolean operations on these types
are open-coded on all types of machines.  Multiplication is open-coded
if the machine supports fullword-to-doubleword a widening multiply
instruction.  Division and shifts are open-coded only on machines that
provide special support.  The operations that are not open-coded use
special library routines that come with GCC@.

There may be pitfalls when you use @code{long long} types for function
arguments, unless you declare function prototypes.  If a function
expects type @code{int} for its argument, and you pass a value of type
@code{long long int}, confusion will result because the caller and the
subroutine will disagree about the number of bytes for the argument.
Likewise, if the function expects @code{long long int} and you pass
@code{int}.  The best way to avoid such problems is to use prototypes.

@node Complex
@section Complex Numbers
@cindex complex numbers
@cindex @code{_Complex} keyword
@cindex @code{__complex__} keyword

ISO C99 supports complex floating data types, and as an extension GCC
supports them in C89 mode and in C++, and supports complex integer data
types which are not part of ISO C99.  You can declare complex types
using the keyword @code{_Complex}.  As an extension, the older GNU
keyword @code{__complex__} is also supported.

For example, @samp{_Complex double x;} declares @code{x} as a
variable whose real part and imaginary part are both of type
@code{double}.  @samp{_Complex short int y;} declares @code{y} to
have real and imaginary parts of type @code{short int}; this is not
likely to be useful, but it shows that the set of complex types is
complete.

To write a constant with a complex data type, use the suffix @samp{i} or
@samp{j} (either one; they are equivalent).  For example, @code{2.5fi}
has type @code{_Complex float} and @code{3i} has type
@code{_Complex int}.  Such a constant always has a pure imaginary
value, but you can form any complex value you like by adding one to a
real constant.  This is a GNU extension; if you have an ISO C99
conforming C library (such as GNU libc), and want to construct complex
constants of floating type, you should include @code{<complex.h>} and
use the macros @code{I} or @code{_Complex_I} instead.

@cindex @code{__real__} keyword
@cindex @code{__imag__} keyword
To extract the real part of a complex-valued expression @var{exp}, write
@code{__real__ @var{exp}}.  Likewise, use @code{__imag__} to
extract the imaginary part.  This is a GNU extension; for values of
floating type, you should use the ISO C99 functions @code{crealf},
@code{creal}, @code{creall}, @code{cimagf}, @code{cimag} and
@code{cimagl}, declared in @code{<complex.h>} and also provided as
built-in functions by GCC@.

@cindex complex conjugation
The operator @samp{~} performs complex conjugation when used on a value
with a complex type.  This is a GNU extension; for values of
floating type, you should use the ISO C99 functions @code{conjf},
@code{conj} and @code{conjl}, declared in @code{<complex.h>} and also
provided as built-in functions by GCC@.

GCC can allocate complex automatic variables in a noncontiguous
fashion; it's even possible for the real part to be in a register while
the imaginary part is on the stack (or vice-versa).  Only the DWARF2
debug info format can represent this, so use of DWARF2 is recommended.
If you are using the stabs debug info format, GCC describes a noncontiguous
complex variable as if it were two separate variables of noncomplex type.
If the variable's actual name is @code{foo}, the two fictitious
variables are named @code{foo$real} and @code{foo$imag}.  You can
examine and set these two fictitious variables with your debugger.

@node Decimal Float
@section Decimal Floating Types
@cindex decimal floating types
@cindex @code{_Decimal32} data type
@cindex @code{_Decimal64} data type
@cindex @code{_Decimal128} data type
@cindex @code{df} integer suffix
@cindex @code{dd} integer suffix
@cindex @code{dl} integer suffix
@cindex @code{DF} integer suffix
@cindex @code{DD} integer suffix
@cindex @code{DL} integer suffix

As an extension, the GNU C compiler supports decimal floating types as
defined in the N1176 draft of ISO/IEC WDTR24732.  Support for decimal
floating types in GCC will evolve as the draft technical report changes.
Calling conventions for any target might also change.  Not all targets
support decimal floating types.

The decimal floating types are @code{_Decimal32}, @code{_Decimal64}, and
@code{_Decimal128}.  They use a radix of ten, unlike the floating types
@code{float}, @code{double}, and @code{long double} whose radix is not
specified by the C standard but is usually two.

Support for decimal floating types includes the arithmetic operators
add, subtract, multiply, divide; unary arithmetic operators;
relational operators; equality operators; and conversions to and from
integer and other floating types.  Use a suffix @samp{df} or
@samp{DF} in a literal constant of type @code{_Decimal32}, @samp{dd}
or @samp{DD} for @code{_Decimal64}, and @samp{dl} or @samp{DL} for
@code{_Decimal128}.

GCC support of decimal float as specified by the draft technical report
is incomplete:

@itemize @bullet
@item
Translation time data type (TTDT) is not supported.

@item
Characteristics of decimal floating types are defined in header file
@file{decfloat.h} rather than @file{float.h}.

@item
When the value of a decimal floating type cannot be represented in the
integer type to which it is being converted, the result is undefined
rather than the result value specified by the draft technical report.
@end itemize

Types @code{_Decimal32}, @code{_Decimal64}, and @code{_Decimal128}
are supported by the DWARF2 debug information format.

@node Hex Floats
@section Hex Floats
@cindex hex floats

ISO C99 supports floating-point numbers written not only in the usual
decimal notation, such as @code{1.55e1}, but also numbers such as
@code{0x1.fp3} written in hexadecimal format.  As a GNU extension, GCC
supports this in C89 mode (except in some cases when strictly
conforming) and in C++.  In that format the
@samp{0x} hex introducer and the @samp{p} or @samp{P} exponent field are
mandatory.  The exponent is a decimal number that indicates the power of
2 by which the significant part will be multiplied.  Thus @samp{0x1.f} is
@tex
$1 {15\over16}$,
@end tex
@ifnottex
1 15/16,
@end ifnottex
@samp{p3} multiplies it by 8, and the value of @code{0x1.fp3}
is the same as @code{1.55e1}.

Unlike for floating-point numbers in the decimal notation the exponent
is always required in the hexadecimal notation.  Otherwise the compiler
would not be able to resolve the ambiguity of, e.g., @code{0x1.f}.  This
could mean @code{1.0f} or @code{1.9375} since @samp{f} is also the
extension for floating-point constants of type @code{float}.

@node Zero Length
@section Arrays of Length Zero
@cindex arrays of length zero
@cindex zero-length arrays
@cindex length-zero arrays
@cindex flexible array members

Zero-length arrays are allowed in GNU C@.  They are very useful as the
last element of a structure which is really a header for a variable-length
object:

@smallexample
struct line @{
  int length;
  char contents[0];
@};

struct line *thisline = (struct line *)
  malloc (sizeof (struct line) + this_length);
thisline->length = this_length;
@end smallexample

In ISO C90, you would have to give @code{contents} a length of 1, which
means either you waste space or complicate the argument to @code{malloc}.

In ISO C99, you would use a @dfn{flexible array member}, which is
slightly different in syntax and semantics:

@itemize @bullet
@item
Flexible array members are written as @code{contents[]} without
the @code{0}.

@item
Flexible array members have incomplete type, and so the @code{sizeof}
operator may not be applied.  As a quirk of the original implementation
of zero-length arrays, @code{sizeof} evaluates to zero.

@item
Flexible array members may only appear as the last member of a
@code{struct} that is otherwise non-empty.

@item
A structure containing a flexible array member, or a union containing
such a structure (possibly recursively), may not be a member of a
structure or an element of an array.  (However, these uses are
permitted by GCC as extensions.)
@end itemize

GCC versions before 3.0 allowed zero-length arrays to be statically
initialized, as if they were flexible arrays.  In addition to those
cases that were useful, it also allowed initializations in situations
that would corrupt later data.  Non-empty initialization of zero-length
arrays is now treated like any case where there are more initializer
elements than the array holds, in that a suitable warning about "excess
elements in array" is given, and the excess elements (all of them, in
this case) are ignored.

Instead GCC allows static initialization of flexible array members.
This is equivalent to defining a new structure containing the original
structure followed by an array of sufficient size to contain the data.
I.e.@: in the following, @code{f1} is constructed as if it were declared
like @code{f2}.

@smallexample
struct f1 @{
  int x; int y[];
@} f1 = @{ 1, @{ 2, 3, 4 @} @};

struct f2 @{
  struct f1 f1; int data[3];
@} f2 = @{ @{ 1 @}, @{ 2, 3, 4 @} @};
@end smallexample

@noindent
The convenience of this extension is that @code{f1} has the desired
type, eliminating the need to consistently refer to @code{f2.f1}.

This has symmetry with normal static arrays, in that an array of
unknown size is also written with @code{[]}.

Of course, this extension only makes sense if the extra data comes at
the end of a top-level object, as otherwise we would be overwriting
data at subsequent offsets.  To avoid undue complication and confusion
with initialization of deeply nested arrays, we simply disallow any
non-empty initialization except when the structure is the top-level
object.  For example:

@smallexample
struct foo @{ int x; int y[]; @};
struct bar @{ struct foo z; @};

struct foo a = @{ 1, @{ 2, 3, 4 @} @};        // @r{Valid.}
struct bar b = @{ @{ 1, @{ 2, 3, 4 @} @} @};    // @r{Invalid.}
struct bar c = @{ @{ 1, @{ @} @} @};            // @r{Valid.}
struct foo d[1] = @{ @{ 1 @{ 2, 3, 4 @} @} @};  // @r{Invalid.}
@end smallexample

@node Empty Structures
@section Structures With No Members
@cindex empty structures
@cindex zero-size structures

GCC permits a C structure to have no members:

@smallexample
struct empty @{
@};
@end smallexample

The structure will have size zero.  In C++, empty structures are part
of the language.  G++ treats empty structures as if they had a single
member of type @code{char}.

@node Variable Length
@section Arrays of Variable Length
@cindex variable-length arrays
@cindex arrays of variable length
@cindex VLAs

Variable-length automatic arrays are allowed in ISO C99, and as an
extension GCC accepts them in C89 mode and in C++.  (However, GCC's
implementation of variable-length arrays does not yet conform in detail
to the ISO C99 standard.)  These arrays are
declared like any other automatic arrays, but with a length that is not
a constant expression.  The storage is allocated at the point of
declaration and deallocated when the brace-level is exited.  For
example:

@smallexample
FILE *
concat_fopen (char *s1, char *s2, char *mode)
@{
  char str[strlen (s1) + strlen (s2) + 1];
  strcpy (str, s1);
  strcat (str, s2);
  return fopen (str, mode);
@}
@end smallexample

@cindex scope of a variable length array
@cindex variable-length array scope
@cindex deallocating variable length arrays
Jumping or breaking out of the scope of the array name deallocates the
storage.  Jumping into the scope is not allowed; you get an error
message for it.

@cindex @code{alloca} vs variable-length arrays
You can use the function @code{alloca} to get an effect much like
variable-length arrays.  The function @code{alloca} is available in
many other C implementations (but not in all).  On the other hand,
variable-length arrays are more elegant.

There are other differences between these two methods.  Space allocated
with @code{alloca} exists until the containing @emph{function} returns.
The space for a variable-length array is deallocated as soon as the array
name's scope ends.  (If you use both variable-length arrays and
@code{alloca} in the same function, deallocation of a variable-length array
will also deallocate anything more recently allocated with @code{alloca}.)

You can also use variable-length arrays as arguments to functions:

@smallexample
struct entry
tester (int len, char data[len][len])
@{
  /* @r{@dots{}} */
@}
@end smallexample

The length of an array is computed once when the storage is allocated
and is remembered for the scope of the array in case you access it with
@code{sizeof}.

If you want to pass the array first and the length afterward, you can
use a forward declaration in the parameter list---another GNU extension.

@smallexample
struct entry
tester (int len; char data[len][len], int len)
@{
  /* @r{@dots{}} */
@}
@end smallexample

@cindex parameter forward declaration
The @samp{int len} before the semicolon is a @dfn{parameter forward
declaration}, and it serves the purpose of making the name @code{len}
known when the declaration of @code{data} is parsed.

You can write any number of such parameter forward declarations in the
parameter list.  They can be separated by commas or semicolons, but the
last one must end with a semicolon, which is followed by the ``real''
parameter declarations.  Each forward declaration must match a ``real''
declaration in parameter name and data type.  ISO C99 does not support
parameter forward declarations.

@node Variadic Macros
@section Macros with a Variable Number of Arguments.
@cindex variable number of arguments
@cindex macro with variable arguments
@cindex rest argument (in macro)
@cindex variadic macros

In the ISO C standard of 1999, a macro can be declared to accept a
variable number of arguments much as a function can.  The syntax for
defining the macro is similar to that of a function.  Here is an
example:

@smallexample
#define debug(format, ...) fprintf (stderr, format, __VA_ARGS__)
@end smallexample

Here @samp{@dots{}} is a @dfn{variable argument}.  In the invocation of
such a macro, it represents the zero or more tokens until the closing
parenthesis that ends the invocation, including any commas.  This set of
tokens replaces the identifier @code{__VA_ARGS__} in the macro body
wherever it appears.  See the CPP manual for more information.

GCC has long supported variadic macros, and used a different syntax that
allowed you to give a name to the variable arguments just like any other
argument.  Here is an example:

@smallexample
#define debug(format, args...) fprintf (stderr, format, args)
@end smallexample

This is in all ways equivalent to the ISO C example above, but arguably
more readable and descriptive.

GNU CPP has two further variadic macro extensions, and permits them to
be used with either of the above forms of macro definition.

In standard C, you are not allowed to leave the variable argument out
entirely; but you are allowed to pass an empty argument.  For example,
this invocation is invalid in ISO C, because there is no comma after
the string:

@smallexample
debug ("A message")
@end smallexample

GNU CPP permits you to completely omit the variable arguments in this
way.  In the above examples, the compiler would complain, though since
the expansion of the macro still has the extra comma after the format
string.

To help solve this problem, CPP behaves specially for variable arguments
used with the token paste operator, @samp{##}.  If instead you write

@smallexample
#define debug(format, ...) fprintf (stderr, format, ## __VA_ARGS__)
@end smallexample

and if the variable arguments are omitted or empty, the @samp{##}
operator causes the preprocessor to remove the comma before it.  If you
do provide some variable arguments in your macro invocation, GNU CPP
does not complain about the paste operation and instead places the
variable arguments after the comma.  Just like any other pasted macro
argument, these arguments are not macro expanded.

@node Escaped Newlines
@section Slightly Looser Rules for Escaped Newlines
@cindex escaped newlines
@cindex newlines (escaped)

Recently, the preprocessor has relaxed its treatment of escaped
newlines.  Previously, the newline had to immediately follow a
backslash.  The current implementation allows whitespace in the form
of spaces, horizontal and vertical tabs, and form feeds between the
backslash and the subsequent newline.  The preprocessor issues a
warning, but treats it as a valid escaped newline and combines the two
lines to form a single logical line.  This works within comments and
tokens, as well as between tokens.  Comments are @emph{not} treated as
whitespace for the purposes of this relaxation, since they have not
yet been replaced with spaces.

@node Subscripting
@section Non-Lvalue Arrays May Have Subscripts
@cindex subscripting
@cindex arrays, non-lvalue

@cindex subscripting and function values
In ISO C99, arrays that are not lvalues still decay to pointers, and
may be subscripted, although they may not be modified or used after
the next sequence point and the unary @samp{&} operator may not be
applied to them.  As an extension, GCC allows such arrays to be
subscripted in C89 mode, though otherwise they do not decay to
pointers outside C99 mode.  For example,
this is valid in GNU C though not valid in C89:

@smallexample
@group
struct foo @{int a[4];@};

struct foo f();

bar (int index)
@{
  return f().a[index];
@}
@end group
@end smallexample

@node Pointer Arith
@section Arithmetic on @code{void}- and Function-Pointers
@cindex void pointers, arithmetic
@cindex void, size of pointer to
@cindex function pointers, arithmetic
@cindex function, size of pointer to

In GNU C, addition and subtraction operations are supported on pointers to
@code{void} and on pointers to functions.  This is done by treating the
size of a @code{void} or of a function as 1.

A consequence of this is that @code{sizeof} is also allowed on @code{void}
and on function types, and returns 1.

@opindex Wpointer-arith
The option @option{-Wpointer-arith} requests a warning if these extensions
are used.

@node Initializers
@section Non-Constant Initializers
@cindex initializers, non-constant
@cindex non-constant initializers

As in standard C++ and ISO C99, the elements of an aggregate initializer for an
automatic variable are not required to be constant expressions in GNU C@.
Here is an example of an initializer with run-time varying elements:

@smallexample
foo (float f, float g)
@{
  float beat_freqs[2] = @{ f-g, f+g @};
  /* @r{@dots{}} */
@}
@end smallexample

@node Compound Literals
@section Compound Literals
@cindex constructor expressions
@cindex initializations in expressions
@cindex structures, constructor expression
@cindex expressions, constructor
@cindex compound literals
@c The GNU C name for what C99 calls compound literals was "constructor expressions".

ISO C99 supports compound literals.  A compound literal looks like
a cast containing an initializer.  Its value is an object of the
type specified in the cast, containing the elements specified in
the initializer; it is an lvalue.  As an extension, GCC supports
compound literals in C89 mode and in C++.

Usually, the specified type is a structure.  Assume that
@code{struct foo} and @code{structure} are declared as shown:

@smallexample
struct foo @{int a; char b[2];@} structure;
@end smallexample

@noindent
Here is an example of constructing a @code{struct foo} with a compound literal:

@smallexample
structure = ((struct foo) @{x + y, 'a', 0@});
@end smallexample

@noindent
This is equivalent to writing the following:

@smallexample
@{
  struct foo temp = @{x + y, 'a', 0@};
  structure = temp;
@}
@end smallexample

You can also construct an array.  If all the elements of the compound literal
are (made up of) simple constant expressions, suitable for use in
initializers of objects of static storage duration, then the compound
literal can be coerced to a pointer to its first element and used in
such an initializer, as shown here:

@smallexample
char **foo = (char *[]) @{ "x", "y", "z" @};
@end smallexample

Compound literals for scalar types and union types are is
also allowed, but then the compound literal is equivalent
to a cast.

As a GNU extension, GCC allows initialization of objects with static storage
duration by compound literals (which is not possible in ISO C99, because
the initializer is not a constant).
It is handled as if the object was initialized only with the bracket
enclosed list if the types of the compound literal and the object match.
The initializer list of the compound literal must be constant.
If the object being initialized has array type of unknown size, the size is
determined by compound literal size.

@smallexample
static struct foo x = (struct foo) @{1, 'a', 'b'@};
static int y[] = (int []) @{1, 2, 3@};
static int z[] = (int [3]) @{1@};
@end smallexample

@noindent
The above lines are equivalent to the following:
@smallexample
static struct foo x = @{1, 'a', 'b'@};
static int y[] = @{1, 2, 3@};
static int z[] = @{1, 0, 0@};
@end smallexample

@node Designated Inits
@section Designated Initializers
@cindex initializers with labeled elements
@cindex labeled elements in initializers
@cindex case labels in initializers
@cindex designated initializers

Standard C89 requires the elements of an initializer to appear in a fixed
order, the same as the order of the elements in the array or structure
being initialized.

In ISO C99 you can give the elements in any order, specifying the array
indices or structure field names they apply to, and GNU C allows this as
an extension in C89 mode as well.  This extension is not
implemented in GNU C++.

To specify an array index, write
@samp{[@var{index}] =} before the element value.  For example,

@smallexample
int a[6] = @{ [4] = 29, [2] = 15 @};
@end smallexample

@noindent
is equivalent to

@smallexample
int a[6] = @{ 0, 0, 15, 0, 29, 0 @};
@end smallexample

@noindent
The index values must be constant expressions, even if the array being
initialized is automatic.

An alternative syntax for this which has been obsolete since GCC 2.5 but
GCC still accepts is to write @samp{[@var{index}]} before the element
value, with no @samp{=}.

To initialize a range of elements to the same value, write
@samp{[@var{first} ... @var{last}] = @var{value}}.  This is a GNU
extension.  For example,

@smallexample
int widths[] = @{ [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 @};
@end smallexample

@noindent
If the value in it has side-effects, the side-effects will happen only once,
not for each initialized field by the range initializer.

@noindent
Note that the length of the array is the highest value specified
plus one.

In a structure initializer, specify the name of a field to initialize
with @samp{.@var{fieldname} =} before the element value.  For example,
given the following structure,

@smallexample
struct point @{ int x, y; @};
@end smallexample

@noindent
the following initialization

@smallexample
struct point p = @{ .y = yvalue, .x = xvalue @};
@end smallexample

@noindent
is equivalent to

@smallexample
struct point p = @{ xvalue, yvalue @};
@end smallexample

Another syntax which has the same meaning, obsolete since GCC 2.5, is
@samp{@var{fieldname}:}, as shown here:

@smallexample
struct point p = @{ y: yvalue, x: xvalue @};
@end smallexample

@cindex designators
The @samp{[@var{index}]} or @samp{.@var{fieldname}} is known as a
@dfn{designator}.  You can also use a designator (or the obsolete colon
syntax) when initializing a union, to specify which element of the union
should be used.  For example,

@smallexample
union foo @{ int i; double d; @};

union foo f = @{ .d = 4 @};
@end smallexample

@noindent
will convert 4 to a @code{double} to store it in the union using
the second element.  By contrast, casting 4 to type @code{union foo}
would store it into the union as the integer @code{i}, since it is
an integer.  (@xref{Cast to Union}.)

You can combine this technique of naming elements with ordinary C
initialization of successive elements.  Each initializer element that
does not have a designator applies to the next consecutive element of the
array or structure.  For example,

@smallexample
int a[6] = @{ [1] = v1, v2, [4] = v4 @};
@end smallexample

@noindent
is equivalent to

@smallexample
int a[6] = @{ 0, v1, v2, 0, v4, 0 @};
@end smallexample

Labeling the elements of an array initializer is especially useful
when the indices are characters or belong to an @code{enum} type.
For example:

@smallexample
int whitespace[256]
  = @{ [' '] = 1, ['\t'] = 1, ['\h'] = 1,
      ['\f'] = 1, ['\n'] = 1, ['\r'] = 1 @};
@end smallexample

@cindex designator lists
You can also write a series of @samp{.@var{fieldname}} and
@samp{[@var{index}]} designators before an @samp{=} to specify a
nested subobject to initialize; the list is taken relative to the
subobject corresponding to the closest surrounding brace pair.  For
example, with the @samp{struct point} declaration above:

@smallexample
struct point ptarray[10] = @{ [2].y = yv2, [2].x = xv2, [0].x = xv0 @};
@end smallexample

@noindent
If the same field is initialized multiple times, it will have value from
the last initialization.  If any such overridden initialization has
side-effect, it is unspecified whether the side-effect happens or not.
Currently, GCC will discard them and issue a warning.

@node Case Ranges
@section Case Ranges
@cindex case ranges
@cindex ranges in case statements

You can specify a range of consecutive values in a single @code{case} label,
like this:

@smallexample
case @var{low} ... @var{high}:
@end smallexample

@noindent
This has the same effect as the proper number of individual @code{case}
labels, one for each integer value from @var{low} to @var{high}, inclusive.

This feature is especially useful for ranges of ASCII character codes:

@smallexample
case 'A' ... 'Z':
@end smallexample

@strong{Be careful:} Write spaces around the @code{...}, for otherwise
it may be parsed wrong when you use it with integer values.  For example,
write this:

@smallexample
case 1 ... 5:
@end smallexample

@noindent
rather than this:

@smallexample
case 1...5:
@end smallexample

@node Cast to Union
@section Cast to a Union Type
@cindex cast to a union
@cindex union, casting to a

A cast to union type is similar to other casts, except that the type
specified is a union type.  You can specify the type either with
@code{union @var{tag}} or with a typedef name.  A cast to union is actually
a constructor though, not a cast, and hence does not yield an lvalue like
normal casts.  (@xref{Compound Literals}.)

The types that may be cast to the union type are those of the members
of the union.  Thus, given the following union and variables:

@smallexample
union foo @{ int i; double d; @};
int x;
double y;
@end smallexample

@noindent
both @code{x} and @code{y} can be cast to type @code{union foo}.

Using the cast as the right-hand side of an assignment to a variable of
union type is equivalent to storing in a member of the union:

@smallexample
union foo u;
/* @r{@dots{}} */
u = (union foo) x  @equiv{}  u.i = x
u = (union foo) y  @equiv{}  u.d = y
@end smallexample

You can also use the union cast as a function argument:

@smallexample
void hack (union foo);
/* @r{@dots{}} */
hack ((union foo) x);
@end smallexample

@node Mixed Declarations
@section Mixed Declarations and Code
@cindex mixed declarations and code
@cindex declarations, mixed with code
@cindex code, mixed with declarations

ISO C99 and ISO C++ allow declarations and code to be freely mixed
within compound statements.  As an extension, GCC also allows this in
C89 mode.  For example, you could do:

@smallexample
int i;
/* @r{@dots{}} */
i++;
int j = i + 2;
@end smallexample

Each identifier is visible from where it is declared until the end of
the enclosing block.

@node Function Attributes
@section Declaring Attributes of Functions
@cindex function attributes
@cindex declaring attributes of functions
@cindex functions that never return
@cindex functions that return more than once
@cindex functions that have no side effects
@cindex functions in arbitrary sections
@cindex functions that behave like malloc
@cindex @code{volatile} applied to function
@cindex @code{const} applied to function
@cindex functions with @code{printf}, @code{scanf}, @code{strftime} or @code{strfmon} style arguments
@cindex functions with non-null pointer arguments
@cindex functions that are passed arguments in registers on the 386
@cindex functions that pop the argument stack on the 386
@cindex functions that do not pop the argument stack on the 386

In GNU C, you declare certain things about functions called in your program
which help the compiler optimize function calls and check your code more
carefully.

The keyword @code{__attribute__} allows you to specify special
attributes when making a declaration.  This keyword is followed by an
attribute specification inside double parentheses.  The following
attributes are currently defined for functions on all targets:
@code{noreturn}, @code{returns_twice}, @code{noinline}, @code{always_inline},
@code{flatten}, @code{pure}, @code{const}, @code{nothrow}, @code{sentinel},
@code{format}, @code{format_arg}, @code{no_instrument_function},
@code{section}, @code{constructor}, @code{destructor}, @code{used},
@code{unused}, @code{deprecated}, @code{weak}, @code{malloc},
@code{alias}, @code{warn_unused_result}, @code{nonnull},
@code{gnu_inline} and @code{externally_visible}.  Several other
attributes are defined for functions on particular target systems.  Other
attributes, including @code{section} are supported for variables declarations
(@pxref{Variable Attributes}) and for types (@pxref{Type Attributes}).

You may also specify attributes with @samp{__} preceding and following
each keyword.  This allows you to use them in header files without
being concerned about a possible macro of the same name.  For example,
you may use @code{__noreturn__} instead of @code{noreturn}.

@xref{Attribute Syntax}, for details of the exact syntax for using
attributes.

@table @code
@c Keep this table alphabetized by attribute name.  Treat _ as space.

@item alias ("@var{target}")
@cindex @code{alias} attribute
The @code{alias} attribute causes the declaration to be emitted as an
alias for another symbol, which must be specified.  For instance,

@smallexample
void __f () @{ /* @r{Do something.} */; @}
void f () __attribute__ ((weak, alias ("__f")));
@end smallexample

defines @samp{f} to be a weak alias for @samp{__f}.  In C++, the
mangled name for the target must be used.  It is an error if @samp{__f}
is not defined in the same translation unit.

Not all target machines support this attribute.

@item always_inline
@cindex @code{always_inline} function attribute
Generally, functions are not inlined unless optimization is specified.
For functions declared inline, this attribute inlines the function even
if no optimization level was specified.

@item gnu_inline
@cindex @code{gnu_inline} function attribute
This attribute should be used with a function which is also declared
with the @code{inline} keyword.  It directs GCC to treat the function
as if it were defined in gnu89 mode even when compiling in C99 or
gnu99 mode.

If the function is declared @code{extern}, then this definition of the
function is used only for inlining.  In no case is the function
compiled as a standalone function, not even if you take its address
explicitly.  Such an address becomes an external reference, as if you
had only declared the function, and had not defined it.  This has
almost the effect of a macro.  The way to use this is to put a
function definition in a header file with this attribute, and put
another copy of the function, without @code{extern}, in a library
file.  The definition in the header file will cause most calls to the
function to be inlined.  If any uses of the function remain, they will
refer to the single copy in the library.  Note that the two
definitions of the functions need not be precisely the same, although
if they do not have the same effect your program may behave oddly.

If the function is neither @code{extern} nor @code{static}, then the
function is compiled as a standalone function, as well as being
inlined where possible.

This is how GCC traditionally handled functions declared
@code{inline}.  Since ISO C99 specifies a different semantics for
@code{inline}, this function attribute is provided as a transition
measure and as a useful feature in its own right.  This attribute is
available in GCC 4.1.3 and later.  It is available if either of the
preprocessor macros @code{__GNUC_GNU_INLINE__} or
@code{__GNUC_STDC_INLINE__} are defined.  @xref{Inline,,An Inline
Function is As Fast As a Macro}.

Note that since the first version of GCC to support C99 inline semantics
is 4.3, earlier versions of GCC which accept this attribute effectively
assume that it is always present, whether or not it is given explicitly.
In versions prior to 4.3, the only effect of explicitly including it is
to disable warnings about using inline functions in C99 mode.

@cindex @code{flatten} function attribute
@item flatten
Generally, inlining into a function is limited.  For a function marked with
this attribute, every call inside this function will be inlined, if possible.
Whether the function itself is considered for inlining depends on its size and
the current inlining parameters.  The @code{flatten} attribute only works
reliably in unit-at-a-time mode.

@item cdecl
@cindex functions that do pop the argument stack on the 386
@opindex mrtd
On the Intel 386, the @code{cdecl} attribute causes the compiler to
assume that the calling function will pop off the stack space used to
pass arguments.  This is
useful to override the effects of the @option{-mrtd} switch.

@item const
@cindex @code{const} function attribute
Many functions do not examine any values except their arguments, and
have no effects except the return value.  Basically this is just slightly
more strict class than the @code{pure} attribute below, since function is not
allowed to read global memory.

@cindex pointer arguments
Note that a function that has pointer arguments and examines the data
pointed to must @emph{not} be declared @code{const}.  Likewise, a
function that calls a non-@code{const} function usually must not be
@code{const}.  It does not make sense for a @code{const} function to
return @code{void}.

The attribute @code{const} is not implemented in GCC versions earlier
than 2.5.  An alternative way to declare that a function has no side
effects, which works in the current version and in some older versions,
is as follows:

@smallexample
typedef int intfn ();

extern const intfn square;
@end smallexample

This approach does not work in GNU C++ from 2.6.0 on, since the language
specifies that the @samp{const} must be attached to the return value.

@item constructor
@itemx destructor
@cindex @code{constructor} function attribute
@cindex @code{destructor} function attribute
The @code{constructor} attribute causes the function to be called
automatically before execution enters @code{main ()}.  Similarly, the
@code{destructor} attribute causes the function to be called
automatically after @code{main ()} has completed or @code{exit ()} has
been called.  Functions with these attributes are useful for
initializing data that will be used implicitly during the execution of
the program.

These attributes are not currently implemented for Objective-C@.

@item deprecated
@cindex @code{deprecated} attribute.
The @code{deprecated} attribute results in a warning if the function
is used anywhere in the source file.  This is useful when identifying
functions that are expected to be removed in a future version of a
program.  The warning also includes the location of the declaration
of the deprecated function, to enable users to easily find further
information about why the function is deprecated, or what they should
do instead.  Note that the warnings only occurs for uses:

@smallexample
int old_fn () __attribute__ ((deprecated));
int old_fn ();
int (*fn_ptr)() = old_fn;
@end smallexample

results in a warning on line 3 but not line 2.

The @code{deprecated} attribute can also be used for variables and
types (@pxref{Variable Attributes}, @pxref{Type Attributes}.)

@item dllexport
@cindex @code{__declspec(dllexport)}
On Microsoft Windows targets and Symbian OS targets the
@code{dllexport} attribute causes the compiler to provide a global
pointer to a pointer in a DLL, so that it can be referenced with the
@code{dllimport} attribute.  On Microsoft Windows targets, the pointer
name is formed by combining @code{_imp__} and the function or variable
name.

You can use @code{__declspec(dllexport)} as a synonym for
@code{__attribute__ ((dllexport))} for compatibility with other
compilers.

On systems that support the @code{visibility} attribute, this
attribute also implies ``default'' visibility, unless a
@code{visibility} attribute is explicitly specified.  You should avoid
the use of @code{dllexport} with ``hidden'' or ``internal''
visibility; in the future GCC may issue an error for those cases.

Currently, the @code{dllexport} attribute is ignored for inlined
functions, unless the @option{-fkeep-inline-functions} flag has been
used.  The attribute is also ignored for undefined symbols.

When applied to C++ classes, the attribute marks defined non-inlined
member functions and static data members as exports.  Static consts
initialized in-class are not marked unless they are also defined
out-of-class.

For Microsoft Windows targets there are alternative methods for
including the symbol in the DLL's export table such as using a
@file{.def} file with an @code{EXPORTS} section or, with GNU ld, using
the @option{--export-all} linker flag.

@item dllimport
@cindex @code{__declspec(dllimport)}
On Microsoft Windows and Symbian OS targets, the @code{dllimport}
attribute causes the compiler to reference a function or variable via
a global pointer to a pointer that is set up by the DLL exporting the
symbol.  The attribute implies @code{extern} storage.  On Microsoft
Windows targets, the pointer name is formed by combining @code{_imp__}
and the function or variable name.

You can use @code{__declspec(dllimport)} as a synonym for
@code{__attribute__ ((dllimport))} for compatibility with other
compilers.

Currently, the attribute is ignored for inlined functions.  If the
attribute is applied to a symbol @emph{definition}, an error is reported.
If a symbol previously declared @code{dllimport} is later defined, the
attribute is ignored in subsequent references, and a warning is emitted.
The attribute is also overridden by a subsequent declaration as
@code{dllexport}.

When applied to C++ classes, the attribute marks non-inlined
member functions and static data members as imports.  However, the
attribute is ignored for virtual methods to allow creation of vtables
using thunks.

On the SH Symbian OS target the @code{dllimport} attribute also has
another affect---it can cause the vtable and run-time type information
for a class to be exported.  This happens when the class has a
dllimport'ed constructor or a non-inline, non-pure virtual function
and, for either of those two conditions, the class also has a inline
constructor or destructor and has a key function that is defined in
the current translation unit.

For Microsoft Windows based targets the use of the @code{dllimport}
attribute on functions is not necessary, but provides a small
performance benefit by eliminating a thunk in the DLL@.  The use of the
@code{dllimport} attribute on imported variables was required on older
versions of the GNU linker, but can now be avoided by passing the
@option{--enable-auto-import} switch to the GNU linker.  As with
functions, using the attribute for a variable eliminates a thunk in
the DLL@.

One drawback to using this attribute is that a pointer to a function
or variable marked as @code{dllimport} cannot be used as a constant
address.  On Microsoft Windows targets, the attribute can be disabled
for functions by setting the @option{-mnop-fun-dllimport} flag.

@item eightbit_data
@cindex eight bit data on the H8/300, H8/300H, and H8S
Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified
variable should be placed into the eight bit data section.
The compiler will generate more efficient code for certain operations
on data in the eight bit data area.  Note the eight bit data area is limited to
256 bytes of data.

You must use GAS and GLD from GNU binutils version 2.7 or later for
this attribute to work correctly.

@item exception_handler
@cindex exception handler functions on the Blackfin processor
Use this attribute on the Blackfin to indicate that the specified function
is an exception handler.  The compiler will generate function entry and
exit sequences suitable for use in an exception handler when this
attribute is present.

@item far
@cindex functions which handle memory bank switching
On 68HC11 and 68HC12 the @code{far} attribute causes the compiler to
use a calling convention that takes care of switching memory banks when
entering and leaving a function.  This calling convention is also the
default when using the @option{-mlong-calls} option.

On 68HC12 the compiler will use the @code{call} and @code{rtc} instructions
to call and return from a function.

On 68HC11 the compiler will generate a sequence of instructions
to invoke a board-specific routine to switch the memory bank and call the
real function.  The board-specific routine simulates a @code{call}.
At the end of a function, it will jump to a board-specific routine
instead of using @code{rts}.  The board-specific return routine simulates
the @code{rtc}.

@item fastcall
@cindex functions that pop the argument stack on the 386
On the Intel 386, the @code{fastcall} attribute causes the compiler to
pass the first argument (if of integral type) in the register ECX and
the second argument (if of integral type) in the register EDX@.  Subsequent
and other typed arguments are passed on the stack.  The called function will
pop the arguments off the stack.  If the number of arguments is variable all
arguments are pushed on the stack.

@item format (@var{archetype}, @var{string-index}, @var{first-to-check})
@cindex @code{format} function attribute
@opindex Wformat
The @code{format} attribute specifies that a function takes @code{printf},
@code{scanf}, @code{strftime} or @code{strfmon} style arguments which
should be type-checked against a format string.  For example, the
declaration:

@smallexample
extern int
my_printf (void *my_object, const char *my_format, ...)
      __attribute__ ((format (printf, 2, 3)));
@end smallexample

@noindent
causes the compiler to check the arguments in calls to @code{my_printf}
for consistency with the @code{printf} style format string argument
@code{my_format}.

The parameter @var{archetype} determines how the format string is
interpreted, and should be @code{printf}, @code{scanf}, @code{strftime}
or @code{strfmon}.  (You can also use @code{__printf__},
@code{__scanf__}, @code{__strftime__} or @code{__strfmon__}.)  The
parameter @var{string-index} specifies which argument is the format
string argument (starting from 1), while @var{first-to-check} is the
number of the first argument to check against the format string.  For
functions where the arguments are not available to be checked (such as
@code{vprintf}), specify the third parameter as zero.  In this case the
compiler only checks the format string for consistency.  For
@code{strftime} formats, the third parameter is required to be zero.
Since non-static C++ methods have an implicit @code{this} argument, the
arguments of such methods should be counted from two, not one, when
giving values for @var{string-index} and @var{first-to-check}.

In the example above, the format string (@code{my_format}) is the second
argument of the function @code{my_print}, and the arguments to check
start with the third argument, so the correct parameters for the format
attribute are 2 and 3.

@opindex ffreestanding
@opindex fno-builtin
The @code{format} attribute allows you to identify your own functions
which take format strings as arguments, so that GCC can check the
calls to these functions for errors.  The compiler always (unless
@option{-ffreestanding} or @option{-fno-builtin} is used) checks formats
for the standard library functions @code{printf}, @code{fprintf},
@code{sprintf}, @code{scanf}, @code{fscanf}, @code{sscanf}, @code{strftime},
@code{vprintf}, @code{vfprintf} and @code{vsprintf} whenever such
warnings are requested (using @option{-Wformat}), so there is no need to
modify the header file @file{stdio.h}.  In C99 mode, the functions
@code{snprintf}, @code{vsnprintf}, @code{vscanf}, @code{vfscanf} and
@code{vsscanf} are also checked.  Except in strictly conforming C
standard modes, the X/Open function @code{strfmon} is also checked as
are @code{printf_unlocked} and @code{fprintf_unlocked}.
@xref{C Dialect Options,,Options Controlling C Dialect}.

The target may provide additional types of format checks.
@xref{Target Format Checks,,Format Checks Specific to Particular
Target Machines}.

@item format_arg (@var{string-index})
@cindex @code{format_arg} function attribute
@opindex Wformat-nonliteral
The @code{format_arg} attribute specifies that a function takes a format
string for a @code{printf}, @code{scanf}, @code{strftime} or
@code{strfmon} style function and modifies it (for example, to translate
it into another language), so the result can be passed to a
@code{printf}, @code{scanf}, @code{strftime} or @code{strfmon} style
function (with the remaining arguments to the format function the same
as they would have been for the unmodified string).  For example, the
declaration:

@smallexample
extern char *
my_dgettext (char *my_domain, const char *my_format)
      __attribute__ ((format_arg (2)));
@end smallexample

@noindent
causes the compiler to check the arguments in calls to a @code{printf},
@code{scanf}, @code{strftime} or @code{strfmon} type function, whose
format string argument is a call to the @code{my_dgettext} function, for
consistency with the format string argument @code{my_format}.  If the
@code{format_arg} attribute had not been specified, all the compiler
could tell in such calls to format functions would be that the format
string argument is not constant; this would generate a warning when
@option{-Wformat-nonliteral} is used, but the calls could not be checked
without the attribute.

The parameter @var{string-index} specifies which argument is the format
string argument (starting from one).  Since non-static C++ methods have
an implicit @code{this} argument, the arguments of such methods should
be counted from two.

The @code{format-arg} attribute allows you to identify your own
functions which modify format strings, so that GCC can check the
calls to @code{printf}, @code{scanf}, @code{strftime} or @code{strfmon}
type function whose operands are a call to one of your own function.
The compiler always treats @code{gettext}, @code{dgettext}, and
@code{dcgettext} in this manner except when strict ISO C support is
requested by @option{-ansi} or an appropriate @option{-std} option, or
@option{-ffreestanding} or @option{-fno-builtin}
is used.  @xref{C Dialect Options,,Options
Controlling C Dialect}.

@item function_vector
@cindex calling functions through the function vector on the H8/300 processors
Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified
function should be called through the function vector.  Calling a
function through the function vector will reduce code size, however;
the function vector has a limited size (maximum 128 entries on the H8/300
and 64 entries on the H8/300H and H8S) and shares space with the interrupt vector.

You must use GAS and GLD from GNU binutils version 2.7 or later for
this attribute to work correctly.

@item interrupt
@cindex interrupt handler functions
Use this attribute on the ARM, AVR, C4x, CRX, M32C, M32R/D, MS1, and Xstormy16
ports to indicate that the specified function is an interrupt handler.
The compiler will generate function entry and exit sequences suitable
for use in an interrupt handler when this attribute is present.

Note, interrupt handlers for the Blackfin, m68k, H8/300, H8/300H, H8S, and
SH processors can be specified via the @code{interrupt_handler} attribute.

Note, on the AVR, interrupts will be enabled inside the function.

Note, for the ARM, you can specify the kind of interrupt to be handled by
adding an optional parameter to the interrupt attribute like this:

@smallexample
void f () __attribute__ ((interrupt ("IRQ")));
@end smallexample

Permissible values for this parameter are: IRQ, FIQ, SWI, ABORT and UNDEF@.

@item interrupt_handler
@cindex interrupt handler functions on the Blackfin, m68k, H8/300 and SH processors
Use this attribute on the Blackfin, m68k, H8/300, H8/300H, H8S, and SH to
indicate that the specified function is an interrupt handler.  The compiler
will generate function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present.

@item kspisusp
@cindex User stack pointer in interrupts on the Blackfin
When used together with @code{interrupt_handler}, @code{exception_handler}
or @code{nmi_handler}, code will be generated to load the stack pointer
from the USP register in the function prologue.

@item long_call/short_call
@cindex indirect calls on ARM
This attribute specifies how a particular function is called on
ARM@.  Both attributes override the @option{-mlong-calls} (@pxref{ARM Options})
command line switch and @code{#pragma long_calls} settings.  The
@code{long_call} attribute indicates that the function might be far
away from the call site and require a different (more expensive)
calling sequence.   The @code{short_call} attribute always places
the offset to the function from the call site into the @samp{BL}
instruction directly.

@item longcall/shortcall
@cindex functions called via pointer on the RS/6000 and PowerPC
On the Blackfin, RS/6000 and PowerPC, the @code{longcall} attribute
indicates that the function might be far away from the call site and
require a different (more expensive) calling sequence.  The
@code{shortcall} attribute indicates that the function is always close
enough for the shorter calling sequence to be used.  These attributes
override both the @option{-mlongcall} switch and, on the RS/6000 and
PowerPC, the @code{#pragma longcall} setting.

@xref{RS/6000 and PowerPC Options}, for more information on whether long
calls are necessary.

@item long_call
@cindex indirect calls on MIPS
This attribute specifies how a particular function is called on MIPS@.
The attribute overrides the @option{-mlong-calls} (@pxref{MIPS Options})
command line switch.  This attribute causes the compiler to always call
the function by first loading its address into a register, and then using
the contents of that register.

@item malloc
@cindex @code{malloc} attribute
The @code{malloc} attribute is used to tell the compiler that a function
may be treated as if any non-@code{NULL} pointer it returns cannot
alias any other pointer valid when the function returns.
This will often improve optimization.
Standard functions with this property include @code{malloc} and
@code{calloc}.  @code{realloc}-like functions have this property as
long as the old pointer is never referred to (including comparing it
to the new pointer) after the function returns a non-@code{NULL}
value.

@item model (@var{model-name})
@cindex function addressability on the M32R/D
@cindex variable addressability on the IA-64

On the M32R/D, use this attribute to set the addressability of an
object, and of the code generated for a function.  The identifier
@var{model-name} is one of @code{small}, @code{medium}, or
@code{large}, representing each of the code models.

Small model objects live in the lower 16MB of memory (so that their
addresses can be loaded with the @code{ld24} instruction), and are
callable with the @code{bl} instruction.

Medium model objects may live anywhere in the 32-bit address space (the
compiler will generate @code{seth/add3} instructions to load their addresses),
and are callable with the @code{bl} instruction.

Large model objects may live anywhere in the 32-bit address space (the
compiler will generate @code{seth/add3} instructions to load their addresses),
and may not be reachable with the @code{bl} instruction (the compiler will
generate the much slower @code{seth/add3/jl} instruction sequence).

On IA-64, use this attribute to set the addressability of an object.
At present, the only supported identifier for @var{model-name} is
@code{small}, indicating addressability via ``small'' (22-bit)
addresses (so that their addresses can be loaded with the @code{addl}
instruction).  Caveat: such addressing is by definition not position
independent and hence this attribute must not be used for objects
defined by shared libraries.

@item naked
@cindex function without a prologue/epilogue code
Use this attribute on the ARM, AVR, C4x and IP2K ports to indicate that the
specified function does not need prologue/epilogue sequences generated by
the compiler.  It is up to the programmer to provide these sequences.

@item near
@cindex functions which do not handle memory bank switching on 68HC11/68HC12
On 68HC11 and 68HC12 the @code{near} attribute causes the compiler to
use the normal calling convention based on @code{jsr} and @code{rts}.
This attribute can be used to cancel the effect of the @option{-mlong-calls}
option.

@item nesting
@cindex Allow nesting in an interrupt handler on the Blackfin processor.
Use this attribute together with @code{interrupt_handler},
@code{exception_handler} or @code{nmi_handler} to indicate that the function
entry code should enable nested interrupts or exceptions.

@item nmi_handler
@cindex NMI handler functions on the Blackfin processor
Use this attribute on the Blackfin to indicate that the specified function
is an NMI handler.  The compiler will generate function entry and
exit sequences suitable for use in an NMI handler when this
attribute is present.

@item no_instrument_function
@cindex @code{no_instrument_function} function attribute
@opindex finstrument-functions
If @option{-finstrument-functions} is given, profiling function calls will
be generated at entry and exit of most user-compiled functions.
Functions with this attribute will not be so instrumented.

@item noinline
@cindex @code{noinline} function attribute
This function attribute prevents a function from being considered for
inlining.

@item nonnull (@var{arg-index}, @dots{})
@cindex @code{nonnull} function attribute
The @code{nonnull} attribute specifies that some function parameters should
be non-null pointers.  For instance, the declaration:

@smallexample
extern void *
my_memcpy (void *dest, const void *src, size_t len)
	__attribute__((nonnull (1, 2)));
@end smallexample

@noindent
causes the compiler to check that, in calls to @code{my_memcpy},
arguments @var{dest} and @var{src} are non-null.  If the compiler
determines that a null pointer is passed in an argument slot marked
as non-null, and the @option{-Wnonnull} option is enabled, a warning
is issued.  The compiler may also choose to make optimizations based
on the knowledge that certain function arguments will not be null.

If no argument index list is given to the @code{nonnull} attribute,
all pointer arguments are marked as non-null.  To illustrate, the
following declaration is equivalent to the previous example:

@smallexample
extern void *
my_memcpy (void *dest, const void *src, size_t len)
	__attribute__((nonnull));
@end smallexample

@item noreturn
@cindex @code{noreturn} function attribute
A few standard library functions, such as @code{abort} and @code{exit},
cannot return.  GCC knows this automatically.  Some programs define
their own functions that never return.  You can declare them
@code{noreturn} to tell the compiler this fact.  For example,

@smallexample
@group
void fatal () __attribute__ ((noreturn));

void
fatal (/* @r{@dots{}} */)
@{
  /* @r{@dots{}} */ /* @r{Print error message.} */ /* @r{@dots{}} */
  exit (1);
@}
@end group
@end smallexample

The @code{noreturn} keyword tells the compiler to assume that
@code{fatal} cannot return.  It can then optimize without regard to what
would happen if @code{fatal} ever did return.  This makes slightly
better code.  More importantly, it helps avoid spurious warnings of
uninitialized variables.

The @code{noreturn} keyword does not affect the exceptional path when that
applies: a @code{noreturn}-marked function may still return to the caller
by throwing an exception or calling @code{longjmp}.

Do not assume that registers saved by the calling function are
restored before calling the @code{noreturn} function.

It does not make sense for a @code{noreturn} function to have a return
type other than @code{void}.

The attribute @code{noreturn} is not implemented in GCC versions
earlier than 2.5.  An alternative way to declare that a function does
not return, which works in the current version and in some older
versions, is as follows:

@smallexample
typedef void voidfn ();

volatile voidfn fatal;
@end smallexample

This approach does not work in GNU C++.

@item nothrow
@cindex @code{nothrow} function attribute
The @code{nothrow} attribute is used to inform the compiler that a
function cannot throw an exception.  For example, most functions in
the standard C library can be guaranteed not to throw an exception
with the notable exceptions of @code{qsort} and @code{bsearch} that
take function pointer arguments.  The @code{nothrow} attribute is not
implemented in GCC versions earlier than 3.3.

@item pure
@cindex @code{pure} function attribute
Many functions have no effects except the return value and their
return value depends only on the parameters and/or global variables.
Such a function can be subject
to common subexpression elimination and loop optimization just as an
arithmetic operator would be.  These functions should be declared
with the attribute @code{pure}.  For example,

@smallexample
int square (int) __attribute__ ((pure));
@end smallexample

@noindent
says that the hypothetical function @code{square} is safe to call
fewer times than the program says.

Some of common examples of pure functions are @code{strlen} or @code{memcmp}.
Interesting non-pure functions are functions with infinite loops or those
depending on volatile memory or other system resource, that may change between
two consecutive calls (such as @code{feof} in a multithreading environment).

The attribute @code{pure} is not implemented in GCC versions earlier
than 2.96.

@item regparm (@var{number})
@cindex @code{regparm} attribute
@cindex functions that are passed arguments in registers on the 386
On the Intel 386, the @code{regparm} attribute causes the compiler to
pass arguments number one to @var{number} if they are of integral type
in registers EAX, EDX, and ECX instead of on the stack.  Functions that
take a variable number of arguments will continue to be passed all of their
arguments on the stack.

Beware that on some ELF systems this attribute is unsuitable for
global functions in shared libraries with lazy binding (which is the
default).  Lazy binding will send the first call via resolving code in
the loader, which might assume EAX, EDX and ECX can be clobbered, as
per the standard calling conventions.  Solaris 8 is affected by this.
GNU systems with GLIBC 2.1 or higher, and FreeBSD, are believed to be
safe since the loaders there save all registers.  (Lazy binding can be
disabled with the linker or the loader if desired, to avoid the
problem.)

@item sseregparm
@cindex @code{sseregparm} attribute
On the Intel 386 with SSE support, the @code{sseregparm} attribute
causes the compiler to pass up to 3 floating point arguments in
SSE registers instead of on the stack.  Functions that take a
variable number of arguments will continue to pass all of their
floating point arguments on the stack.

@item force_align_arg_pointer
@cindex @code{force_align_arg_pointer} attribute
On the Intel x86, the @code{force_align_arg_pointer} attribute may be
applied to individual function definitions, generating an alternate
prologue and epilogue that realigns the runtime stack.  This supports
mixing legacy codes that run with a 4-byte aligned stack with modern
codes that keep a 16-byte stack for SSE compatibility.  The alternate
prologue and epilogue are slower and bigger than the regular ones, and
the alternate prologue requires a scratch register; this lowers the
number of registers available if used in conjunction with the
@code{regparm} attribute.  The @code{force_align_arg_pointer}
attribute is incompatible with nested functions; this is considered a
hard error.

@item returns_twice
@cindex @code{returns_twice} attribute
The @code{returns_twice} attribute tells the compiler that a function may
return more than one time.  The compiler will ensure that all registers
are dead before calling such a function and will emit a warning about
the variables that may be clobbered after the second return from the
function.  Examples of such functions are @code{setjmp} and @code{vfork}.
The @code{longjmp}-like counterpart of such function, if any, might need
to be marked with the @code{noreturn} attribute.

@item saveall
@cindex save all registers on the Blackfin, H8/300, H8/300H, and H8S
Use this attribute on the Blackfin, H8/300, H8/300H, and H8S to indicate that
all registers except the stack pointer should be saved in the prologue
regardless of whether they are used or not.

@item section ("@var{section-name}")
@cindex @code{section} function attribute
Normally, the compiler places the code it generates in the @code{text} section.
Sometimes, however, you need additional sections, or you need certain
particular functions to appear in special sections.  The @code{section}
attribute specifies that a function lives in a particular section.
For example, the declaration:

@smallexample
extern void foobar (void) __attribute__ ((section ("bar")));
@end smallexample

@noindent
puts the function @code{foobar} in the @code{bar} section.

Some file formats do not support arbitrary sections so the @code{section}
attribute is not available on all platforms.
If you need to map the entire contents of a module to a particular
section, consider using the facilities of the linker instead.

@item sentinel
@cindex @code{sentinel} function attribute
This function attribute ensures that a parameter in a function call is
an explicit @code{NULL}.  The attribute is only valid on variadic
functions.  By default, the sentinel is located at position zero, the
last parameter of the function call.  If an optional integer position
argument P is supplied to the attribute, the sentinel must be located at
position P counting backwards from the end of the argument list.

@smallexample
__attribute__ ((sentinel))
is equivalent to
__attribute__ ((sentinel(0)))
@end smallexample

The attribute is automatically set with a position of 0 for the built-in
functions @code{execl} and @code{execlp}.  The built-in function
@code{execle} has the attribute set with a position of 1.

A valid @code{NULL} in this context is defined as zero with any pointer
type.  If your system defines the @code{NULL} macro with an integer type
then you need to add an explicit cast.  GCC replaces @code{stddef.h}
with a copy that redefines NULL appropriately.

The warnings for missing or incorrect sentinels are enabled with
@option{-Wformat}.

@item short_call
See long_call/short_call.

@item shortcall
See longcall/shortcall.

@item signal
@cindex signal handler functions on the AVR processors
Use this attribute on the AVR to indicate that the specified
function is a signal handler.  The compiler will generate function
entry and exit sequences suitable for use in a signal handler when this
attribute is present.  Interrupts will be disabled inside the function.

@item sp_switch
Use this attribute on the SH to indicate an @code{interrupt_handler}
function should switch to an alternate stack.  It expects a string
argument that names a global variable holding the address of the
alternate stack.

@smallexample
void *alt_stack;
void f () __attribute__ ((interrupt_handler,
                          sp_switch ("alt_stack")));
@end smallexample

@item stdcall
@cindex functions that pop the argument stack on the 386
On the Intel 386, the @code{stdcall} attribute causes the compiler to
assume that the called function will pop off the stack space used to
pass arguments, unless it takes a variable number of arguments.

@item tiny_data
@cindex tiny data section on the H8/300H and H8S
Use this attribute on the H8/300H and H8S to indicate that the specified
variable should be placed into the tiny data section.
The compiler will generate more efficient code for loads and stores
on data in the tiny data section.  Note the tiny data area is limited to
slightly under 32kbytes of data.

@item trap_exit
Use this attribute on the SH for an @code{interrupt_handler} to return using
@code{trapa} instead of @code{rte}.  This attribute expects an integer
argument specifying the trap number to be used.

@item unused
@cindex @code{unused} attribute.
This attribute, attached to a function, means that the function is meant
to be possibly unused.  GCC will not produce a warning for this
function.

@item used
@cindex @code{used} attribute.
This attribute, attached to a function, means that code must be emitted
for the function even if it appears that the function is not referenced.
This is useful, for example, when the function is referenced only in
inline assembly.

@item visibility ("@var{visibility_type}")
@cindex @code{visibility} attribute
This attribute affects the linkage of the declaration to which it is attached.
There are four supported @var{visibility_type} values: default,
hidden, protected or internal visibility.

@smallexample
void __attribute__ ((visibility ("protected")))
f () @{ /* @r{Do something.} */; @}
int i __attribute__ ((visibility ("hidden")));
@end smallexample

The possible values of @var{visibility_type} correspond to the
visibility settings in the ELF gABI.

@table @dfn
@c keep this list of visibilities in alphabetical order.

@item default
Default visibility is the normal case for the object file format.
This value is available for the visibility attribute to override other
options that may change the assumed visibility of entities.

On ELF, default visibility means that the declaration is visible to other
modules and, in shared libraries, means that the declared entity may be
overridden.

On Darwin, default visibility means that the declaration is visible to
other modules.

Default visibility corresponds to ``external linkage'' in the language.

@item hidden
Hidden visibility indicates that the entity declared will have a new
form of linkage, which we'll call ``hidden linkage''.  Two
declarations of an object with hidden linkage refer to the same object
if they are in the same shared object.

@item internal
Internal visibility is like hidden visibility, but with additional
processor specific semantics.  Unless otherwise specified by the
psABI, GCC defines internal visibility to mean that a function is
@emph{never} called from another module.  Compare this with hidden
functions which, while they cannot be referenced directly by other
modules, can be referenced indirectly via function pointers.  By
indicating that a function cannot be called from outside the module,
GCC may for instance omit the load of a PIC register since it is known
that the calling function loaded the correct value.

@item protected
Protected visibility is like default visibility except that it
indicates that references within the defining module will bind to the
definition in that module.  That is, the declared entity cannot be
overridden by another module.

@end table

All visibilities are supported on many, but not all, ELF targets
(supported when the assembler supports the @samp{.visibility}
pseudo-op).  Default visibility is supported everywhere.  Hidden
visibility is supported on Darwin targets.

The visibility attribute should be applied only to declarations which
would otherwise have external linkage.  The attribute should be applied
consistently, so that the same entity should not be declared with
different settings of the attribute.

In C++, the visibility attribute applies to types as well as functions
and objects, because in C++ types have linkage.  A class must not have
greater visibility than its non-static data member types and bases,
and class members default to the visibility of their class.  Also, a
declaration without explicit visibility is limited to the visibility
of its type.

In C++, you can mark member functions and static member variables of a
class with the visibility attribute.  This is useful if if you know a
particular method or static member variable should only be used from
one shared object; then you can mark it hidden while the rest of the
class has default visibility.  Care must be taken to avoid breaking
the One Definition Rule; for example, it is usually not useful to mark
an inline method as hidden without marking the whole class as hidden.

A C++ namespace declaration can also have the visibility attribute.
This attribute applies only to the particular namespace body, not to
other definitions of the same namespace; it is equivalent to using
@samp{#pragma GCC visibility} before and after the namespace
definition (@pxref{Visibility Pragmas}).

In C++, if a template argument has limited visibility, this
restriction is implicitly propagated to the template instantiation.
Otherwise, template instantiations and specializations default to the
visibility of their template.

If both the template and enclosing class have explicit visibility, the
visibility from the template is used.

@item warn_unused_result
@cindex @code{warn_unused_result} attribute
The @code{warn_unused_result} attribute causes a warning to be emitted
if a caller of the function with this attribute does not use its
return value.  This is useful for functions where not checking
the result is either a security problem or always a bug, such as
@code{realloc}.

@smallexample
int fn () __attribute__ ((warn_unused_result));
int foo ()
@{
  if (fn () < 0) return -1;
  fn ();
  return 0;
@}
@end smallexample

results in warning on line 5.

@item weak
@cindex @code{weak} attribute
The @code{weak} attribute causes the declaration to be emitted as a weak
symbol rather than a global.  This is primarily useful in defining
library functions which can be overridden in user code, though it can
also be used with non-function declarations.  Weak symbols are supported
for ELF targets, and also for a.out targets when using the GNU assembler
and linker.

@item weakref
@itemx weakref ("@var{target}")
@cindex @code{weakref} attribute
The @code{weakref} attribute marks a declaration as a weak reference.
Without arguments, it should be accompanied by an @code{alias} attribute
naming the target symbol.  Optionally, the @var{target} may be given as
an argument to @code{weakref} itself.  In either case, @code{weakref}
implicitly marks the declaration as @code{weak}.  Without a
@var{target}, given as an argument to @code{weakref} or to @code{alias},
@code{weakref} is equivalent to @code{weak}.

@smallexample
static int x() __attribute__ ((weakref ("y")));
/* is equivalent to... */
static int x() __attribute__ ((weak, weakref, alias ("y")));
/* and to... */
static int x() __attribute__ ((weakref));
static int x() __attribute__ ((alias ("y")));
@end smallexample

A weak reference is an alias that does not by itself require a
definition to be given for the target symbol.  If the target symbol is
only referenced through weak references, then the becomes a @code{weak}
undefined symbol.  If it is directly referenced, however, then such
strong references prevail, and a definition will be required for the
symbol, not necessarily in the same translation unit.

The effect is equivalent to moving all references to the alias to a
separate translation unit, renaming the alias to the aliased symbol,
declaring it as weak, compiling the two separate translation units and
performing a reloadable link on them.

At present, a declaration to which @code{weakref} is attached can
only be @code{static}.

@item externally_visible
@cindex @code{externally_visible} attribute.
This attribute, attached to a global variable or function nullify
effect of @option{-fwhole-program} command line option, so the object
remain visible outside the current compilation unit

@end table

You can specify multiple attributes in a declaration by separating them
by commas within the double parentheses or by immediately following an
attribute declaration with another attribute declaration.

@cindex @code{#pragma}, reason for not using
@cindex pragma, reason for not using
Some people object to the @code{__attribute__} feature, suggesting that
ISO C's @code{#pragma} should be used instead.  At the time
@code{__attribute__} was designed, there were two reasons for not doing
this.

@enumerate
@item
It is impossible to generate @code{#pragma} commands from a macro.

@item
There is no telling what the same @code{#pragma} might mean in another
compiler.
@end enumerate

These two reasons applied to almost any application that might have been
proposed for @code{#pragma}.  It was basically a mistake to use
@code{#pragma} for @emph{anything}.

The ISO C99 standard includes @code{_Pragma}, which now allows pragmas
to be generated from macros.  In addition, a @code{#pragma GCC}
namespace is now in use for GCC-specific pragmas.  However, it has been
found convenient to use @code{__attribute__} to achieve a natural
attachment of attributes to their corresponding declarations, whereas
@code{#pragma GCC} is of use for constructs that do not naturally form
part of the grammar.  @xref{Other Directives,,Miscellaneous
Preprocessing Directives, cpp, The GNU C Preprocessor}.

@node Attribute Syntax
@section Attribute Syntax
@cindex attribute syntax

This section describes the syntax with which @code{__attribute__} may be
used, and the constructs to which attribute specifiers bind, for the C
language.  Some details may vary for C++ and Objective-C@.  Because of
infelicities in the grammar for attributes, some forms described here
may not be successfully parsed in all cases.

There are some problems with the semantics of attributes in C++.  For
example, there are no manglings for attributes, although they may affect
code generation, so problems may arise when attributed types are used in
conjunction with templates or overloading.  Similarly, @code{typeid}
does not distinguish between types with different attributes.  Support
for attributes in C++ may be restricted in future to attributes on
declarations only, but not on nested declarators.

@xref{Function Attributes}, for details of the semantics of attributes
applying to functions.  @xref{Variable Attributes}, for details of the
semantics of attributes applying to variables.  @xref{Type Attributes},
for details of the semantics of attributes applying to structure, union
and enumerated types.

An @dfn{attribute specifier} is of the form
@code{__attribute__ ((@var{attribute-list}))}.  An @dfn{attribute list}
is a possibly empty comma-separated sequence of @dfn{attributes}, where
each attribute is one of the following:

@itemize @bullet
@item
Empty.  Empty attributes are ignored.

@item
A word (which may be an identifier such as @code{unused}, or a reserved
word such as @code{const}).

@item
A word, followed by, in parentheses, parameters for the attribute.
These parameters take one of the following forms:

@itemize @bullet
@item
An identifier.  For example, @code{mode} attributes use this form.

@item
An identifier followed by a comma and a non-empty comma-separated list
of expressions.  For example, @code{format} attributes use this form.

@item
A possibly empty comma-separated list of expressions.  For example,
@code{format_arg} attributes use this form with the list being a single
integer constant expression, and @code{alias} attributes use this form
with the list being a single string constant.
@end itemize
@end itemize

An @dfn{attribute specifier list} is a sequence of one or more attribute
specifiers, not separated by any other tokens.

In GNU C, an attribute specifier list may appear after the colon following a
label, other than a @code{case} or @code{default} label.  The only
attribute it makes sense to use after a label is @code{unused}.  This
feature is intended for code generated by programs which contains labels
that may be unused but which is compiled with @option{-Wall}.  It would
not normally be appropriate to use in it human-written code, though it
could be useful in cases where the code that jumps to the label is
contained within an @code{#ifdef} conditional.  GNU C++ does not permit
such placement of attribute lists, as it is permissible for a
declaration, which could begin with an attribute list, to be labelled in
C++.  Declarations cannot be labelled in C90 or C99, so the ambiguity
does not arise there.

An attribute specifier list may appear as part of a @code{struct},
@code{union} or @code{enum} specifier.  It may go either immediately
after the @code{struct}, @code{union} or @code{enum} keyword, or after
the closing brace.  The former syntax is preferred.
Where attribute specifiers follow the closing brace, they are considered
to relate to the structure, union or enumerated type defined, not to any
enclosing declaration the type specifier appears in, and the type
defined is not complete until after the attribute specifiers.
@c Otherwise, there would be the following problems: a shift/reduce
@c conflict between attributes binding the struct/union/enum and
@c binding to the list of specifiers/qualifiers; and "aligned"
@c attributes could use sizeof for the structure, but the size could be
@c changed later by "packed" attributes.

Otherwise, an attribute specifier appears as part of a declaration,
counting declarations of unnamed parameters and type names, and relates
to that declaration (which may be nested in another declaration, for
example in the case of a parameter declaration), or to a particular declarator
within a declaration.  Where an
attribute specifier is applied to a parameter declared as a function or
an array, it should apply to the function or array rather than the
pointer to which the parameter is implicitly converted, but this is not
yet correctly implemented.

Any list of specifiers and qualifiers at the start of a declaration may
contain attribute specifiers, whether or not such a list may in that
context contain storage class specifiers.  (Some attributes, however,
are essentially in the nature of storage class specifiers, and only make
sense where storage class specifiers may be used; for example,
@code{section}.)  There is one necessary limitation to this syntax: the
first old-style parameter declaration in a function definition cannot
begin with an attribute specifier, because such an attribute applies to
the function instead by syntax described below (which, however, is not
yet implemented in this case).  In some other cases, attribute
specifiers are permitted by this grammar but not yet supported by the
compiler.  All attribute specifiers in this place relate to the
declaration as a whole.  In the obsolescent usage where a type of
@code{int} is implied by the absence of type specifiers, such a list of
specifiers and qualifiers may be an attribute specifier list with no
other specifiers or qualifiers.

At present, the first parameter in a function prototype must have some
type specifier which is not an attribute specifier; this resolves an
ambiguity in the interpretation of @code{void f(int
(__attribute__((foo)) x))}, but is subject to change.  At present, if
the parentheses of a function declarator contain only attributes then
those attributes are ignored, rather than yielding an error or warning
or implying a single parameter of type int, but this is subject to
change.

An attribute specifier list may appear immediately before a declarator
(other than the first) in a comma-separated list of declarators in a
declaration of more than one identifier using a single list of
specifiers and qualifiers.  Such attribute specifiers apply
only to the identifier before whose declarator they appear.  For
example, in

@smallexample
__attribute__((noreturn)) void d0 (void),
    __attribute__((format(printf, 1, 2))) d1 (const char *, ...),
     d2 (void)
@end smallexample

@noindent
the @code{noreturn} attribute applies to all the functions
declared; the @code{format} attribute only applies to @code{d1}.

An attribute specifier list may appear immediately before the comma,
@code{=} or semicolon terminating the declaration of an identifier other
than a function definition.  At present, such attribute specifiers apply
to the declared object or function, but in future they may attach to the
outermost adjacent declarator.  In simple cases there is no difference,
but, for example, in

@smallexample
void (****f)(void) __attribute__((noreturn));
@end smallexample

@noindent
at present the @code{noreturn} attribute applies to @code{f}, which
causes a warning since @code{f} is not a function, but in future it may
apply to the function @code{****f}.  The precise semantics of what
attributes in such cases will apply to are not yet specified.  Where an
assembler name for an object or function is specified (@pxref{Asm
Labels}), at present the attribute must follow the @code{asm}
specification; in future, attributes before the @code{asm} specification
may apply to the adjacent declarator, and those after it to the declared
object or function.

An attribute specifier list may, in future, be permitted to appear after
the declarator in a function definition (before any old-style parameter
declarations or the function body).

Attribute specifiers may be mixed with type qualifiers appearing inside
the @code{[]} of a parameter array declarator, in the C99 construct by
which such qualifiers are applied to the pointer to which the array is
implicitly converted.  Such attribute specifiers apply to the pointer,
not to the array, but at present this is not implemented and they are
ignored.

An attribute specifier list may appear at the start of a nested
declarator.  At present, there are some limitations in this usage: the
attributes correctly apply to the declarator, but for most individual
attributes the semantics this implies are not implemented.
When attribute specifiers follow the @code{*} of a pointer
declarator, they may be mixed with any type qualifiers present.
The following describes the formal semantics of this syntax.  It will make the
most sense if you are familiar with the formal specification of
declarators in the ISO C standard.

Consider (as in C99 subclause 6.7.5 paragraph 4) a declaration @code{T
D1}, where @code{T} contains declaration specifiers that specify a type
@var{Type} (such as @code{int}) and @code{D1} is a declarator that
contains an identifier @var{ident}.  The type specified for @var{ident}
for derived declarators whose type does not include an attribute
specifier is as in the ISO C standard.

If @code{D1} has the form @code{( @var{attribute-specifier-list} D )},
and the declaration @code{T D} specifies the type
``@var{derived-declarator-type-list} @var{Type}'' for @var{ident}, then
@code{T D1} specifies the type ``@var{derived-declarator-type-list}
@var{attribute-specifier-list} @var{Type}'' for @var{ident}.

If @code{D1} has the form @code{*
@var{type-qualifier-and-attribute-specifier-list} D}, and the
declaration @code{T D} specifies the type
``@var{derived-declarator-type-list} @var{Type}'' for @var{ident}, then
@code{T D1} specifies the type ``@var{derived-declarator-type-list}
@var{type-qualifier-and-attribute-specifier-list} @var{Type}'' for
@var{ident}.

For example,

@smallexample
void (__attribute__((noreturn)) ****f) (void);
@end smallexample

@noindent
specifies the type ``pointer to pointer to pointer to pointer to
non-returning function returning @code{void}''.  As another example,

@smallexample
char *__attribute__((aligned(8))) *f;
@end smallexample

@noindent
specifies the type ``pointer to 8-byte-aligned pointer to @code{char}''.
Note again that this does not work with most attributes; for example,
the usage of @samp{aligned} and @samp{noreturn} attributes given above
is not yet supported.

For compatibility with existing code written for compiler versions that
did not implement attributes on nested declarators, some laxity is
allowed in the placing of attributes.  If an attribute that only applies
to types is applied to a declaration, it will be treated as applying to
the type of that declaration.  If an attribute that only applies to
declarations is applied to the type of a declaration, it will be treated
as applying to that declaration; and, for compatibility with code
placing the attributes immediately before the identifier declared, such
an attribute applied to a function return type will be treated as
applying to the function type, and such an attribute applied to an array
element type will be treated as applying to the array type.  If an
attribute that only applies to function types is applied to a
pointer-to-function type, it will be treated as applying to the pointer
target type; if such an attribute is applied to a function return type
that is not a pointer-to-function type, it will be treated as applying
to the function type.

@node Function Prototypes
@section Prototypes and Old-Style Function Definitions
@cindex function prototype declarations
@cindex old-style function definitions
@cindex promotion of formal parameters

GNU C extends ISO C to allow a function prototype to override a later
old-style non-prototype definition.  Consider the following example:

@smallexample
/* @r{Use prototypes unless the compiler is old-fashioned.}  */
#ifdef __STDC__
#define P(x) x
#else
#define P(x) ()
#endif

/* @r{Prototype function declaration.}  */
int isroot P((uid_t));

/* @r{Old-style function definition.}  */
int
isroot (x)   /* @r{??? lossage here ???} */
     uid_t x;
@{
  return x == 0;
@}
@end smallexample

Suppose the type @code{uid_t} happens to be @code{short}.  ISO C does
not allow this example, because subword arguments in old-style
non-prototype definitions are promoted.  Therefore in this example the
function definition's argument is really an @code{int}, which does not
match the prototype argument type of @code{short}.

This restriction of ISO C makes it hard to write code that is portable
to traditional C compilers, because the programmer does not know
whether the @code{uid_t} type is @code{short}, @code{int}, or
@code{long}.  Therefore, in cases like these GNU C allows a prototype
to override a later old-style definition.  More precisely, in GNU C, a
function prototype argument type overrides the argument type specified
by a later old-style definition if the former type is the same as the
latter type before promotion.  Thus in GNU C the above example is
equivalent to the following:

@smallexample
int isroot (uid_t);

int
isroot (uid_t x)
@{
  return x == 0;
@}
@end smallexample

@noindent
GNU C++ does not support old-style function definitions, so this
extension is irrelevant.

@node C++ Comments
@section C++ Style Comments
@cindex //
@cindex C++ comments
@cindex comments, C++ style

In GNU C, you may use C++ style comments, which start with @samp{//} and
continue until the end of the line.  Many other C implementations allow
such comments, and they are included in the 1999 C standard.  However,
C++ style comments are not recognized if you specify an @option{-std}
option specifying a version of ISO C before C99, or @option{-ansi}
(equivalent to @option{-std=c89}).

@node Dollar Signs
@section Dollar Signs in Identifier Names
@cindex $
@cindex dollar signs in identifier names
@cindex identifier names, dollar signs in

In GNU C, you may normally use dollar signs in identifier names.
This is because many traditional C implementations allow such identifiers.
However, dollar signs in identifiers are not supported on a few target
machines, typically because the target assembler does not allow them.

@node Character Escapes
@section The Character @key{ESC} in Constants

You can use the sequence @samp{\e} in a string or character constant to
stand for the ASCII character @key{ESC}.

@node Alignment
@section Inquiring on Alignment of Types or Variables
@cindex alignment
@cindex type alignment
@cindex variable alignment

The keyword @code{__alignof__} allows you to inquire about how an object
is aligned, or the minimum alignment usually required by a type.  Its
syntax is just like @code{sizeof}.

For example, if the target machine requires a @code{double} value to be
aligned on an 8-byte boundary, then @code{__alignof__ (double)} is 8.
This is true on many RISC machines.  On more traditional machine
designs, @code{__alignof__ (double)} is 4 or even 2.

Some machines never actually require alignment; they allow reference to any
data type even at an odd address.  For these machines, @code{__alignof__}
reports the @emph{recommended} alignment of a type.

If the operand of @code{__alignof__} is an lvalue rather than a type,
its value is the required alignment for its type, taking into account
any minimum alignment specified with GCC's @code{__attribute__}
extension (@pxref{Variable Attributes}).  For example, after this
declaration:

@smallexample
struct foo @{ int x; char y; @} foo1;
@end smallexample

@noindent
the value of @code{__alignof__ (foo1.y)} is 1, even though its actual
alignment is probably 2 or 4, the same as @code{__alignof__ (int)}.

It is an error to ask for the alignment of an incomplete type.

@node Variable Attributes
@section Specifying Attributes of Variables
@cindex attribute of variables
@cindex variable attributes

The keyword @code{__attribute__} allows you to specify special
attributes of variables or structure fields.  This keyword is followed
by an attribute specification inside double parentheses.  Some
attributes are currently defined generically for variables.
Other attributes are defined for variables on particular target
systems.  Other attributes are available for functions
(@pxref{Function Attributes}) and for types (@pxref{Type Attributes}).
Other front ends might define more attributes
(@pxref{C++ Extensions,,Extensions to the C++ Language}).

You may also specify attributes with @samp{__} preceding and following
each keyword.  This allows you to use them in header files without
being concerned about a possible macro of the same name.  For example,
you may use @code{__aligned__} instead of @code{aligned}.

@xref{Attribute Syntax}, for details of the exact syntax for using
attributes.

@table @code
@cindex @code{aligned} attribute
@item aligned (@var{alignment})
This attribute specifies a minimum alignment for the variable or
structure field, measured in bytes.  For example, the declaration:

@smallexample
int x __attribute__ ((aligned (16))) = 0;
@end smallexample

@noindent
causes the compiler to allocate the global variable @code{x} on a
16-byte boundary.  On a 68040, this could be used in conjunction with
an @code{asm} expression to access the @code{move16} instruction which
requires 16-byte aligned operands.

You can also specify the alignment of structure fields.  For example, to
create a double-word aligned @code{int} pair, you could write:

@smallexample
struct foo @{ int x[2] __attribute__ ((aligned (8))); @};
@end smallexample

@noindent
This is an alternative to creating a union with a @code{double} member
that forces the union to be double-word aligned.

As in the preceding examples, you can explicitly specify the alignment
(in bytes) that you wish the compiler to use for a given variable or
structure field.  Alternatively, you can leave out the alignment factor
and just ask the compiler to align a variable or field to the maximum
useful alignment for the target machine you are compiling for.  For
example, you could write:

@smallexample
short array[3] __attribute__ ((aligned));
@end smallexample

Whenever you leave out the alignment factor in an @code{aligned} attribute
specification, the compiler automatically sets the alignment for the declared
variable or field to the largest alignment which is ever used for any data
type on the target machine you are compiling for.  Doing this can often make
copy operations more efficient, because the compiler can use whatever
instructions copy the biggest chunks of memory when performing copies to
or from the variables or fields that you have aligned this way.

The @code{aligned} attribute can only increase the alignment; but you
can decrease it by specifying @code{packed} as well.  See below.

Note that the effectiveness of @code{aligned} attributes may be limited
by inherent limitations in your linker.  On many systems, the linker is
only able to arrange for variables to be aligned up to a certain maximum
alignment.  (For some linkers, the maximum supported alignment may
be very very small.)  If your linker is only able to align variables
up to a maximum of 8 byte alignment, then specifying @code{aligned(16)}
in an @code{__attribute__} will still only provide you with 8 byte
alignment.  See your linker documentation for further information.

@item cleanup (@var{cleanup_function})
@cindex @code{cleanup} attribute
The @code{cleanup} attribute runs a function when the variable goes
out of scope.  This attribute can only be applied to auto function
scope variables; it may not be applied to parameters or variables
with static storage duration.  The function must take one parameter,
a pointer to a type compatible with the variable.  The return value
of the function (if any) is ignored.

If @option{-fexceptions} is enabled, then @var{cleanup_function}
will be run during the stack unwinding that happens during the
processing of the exception.  Note that the @code{cleanup} attribute
does not allow the exception to be caught, only to perform an action.
It is undefined what happens if @var{cleanup_function} does not
return normally.

@item common
@itemx nocommon
@cindex @code{common} attribute
@cindex @code{nocommon} attribute
@opindex fcommon
@opindex fno-common
The @code{common} attribute requests GCC to place a variable in
``common'' storage.  The @code{nocommon} attribute requests the
opposite---to allocate space for it directly.

These attributes override the default chosen by the
@option{-fno-common} and @option{-fcommon} flags respectively.

@item deprecated
@cindex @code{deprecated} attribute
The @code{deprecated} attribute results in a warning if the variable
is used anywhere in the source file.  This is useful when identifying
variables that are expected to be removed in a future version of a
program.  The warning also includes the location of the declaration
of the deprecated variable, to enable users to easily find further
information about why the variable is deprecated, or what they should
do instead.  Note that the warning only occurs for uses:

@smallexample
extern int old_var __attribute__ ((deprecated));
extern int old_var;
int new_fn () @{ return old_var; @}
@end smallexample

results in a warning on line 3 but not line 2.

The @code{deprecated} attribute can also be used for functions and
types (@pxref{Function Attributes}, @pxref{Type Attributes}.)

@item mode (@var{mode})
@cindex @code{mode} attribute
This attribute specifies the data type for the declaration---whichever
type corresponds to the mode @var{mode}.  This in effect lets you
request an integer or floating point type according to its width.

You may also specify a mode of @samp{byte} or @samp{__byte__} to
indicate the mode corresponding to a one-byte integer, @samp{word} or
@samp{__word__} for the mode of a one-word integer, and @samp{pointer}
or @samp{__pointer__} for the mode used to represent pointers.

@item packed
@cindex @code{packed} attribute
The @code{packed} attribute specifies that a variable or structure field
should have the smallest possible alignment---one byte for a variable,
and one bit for a field, unless you specify a larger value with the
@code{aligned} attribute.

Here is a structure in which the field @code{x} is packed, so that it
immediately follows @code{a}:

@smallexample
struct foo
@{
  char a;
  int x[2] __attribute__ ((packed));
@};
@end smallexample

@item section ("@var{section-name}")
@cindex @code{section} variable attribute
Normally, the compiler places the objects it generates in sections like
@code{data} and @code{bss}.  Sometimes, however, you need additional sections,
or you need certain particular variables to appear in special sections,
for example to map to special hardware.  The @code{section}
attribute specifies that a variable (or function) lives in a particular
section.  For example, this small program uses several specific section names:

@smallexample
struct duart a __attribute__ ((section ("DUART_A"))) = @{ 0 @};
struct duart b __attribute__ ((section ("DUART_B"))) = @{ 0 @};
char stack[10000] __attribute__ ((section ("STACK"))) = @{ 0 @};
int init_data __attribute__ ((section ("INITDATA"))) = 0;

main()
@{
  /* @r{Initialize stack pointer} */
  init_sp (stack + sizeof (stack));

  /* @r{Initialize initialized data} */
  memcpy (&init_data, &data, &edata - &data);

  /* @r{Turn on the serial ports} */
  init_duart (&a);
  init_duart (&b);
@}
@end smallexample

@noindent
Use the @code{section} attribute with an @emph{initialized} definition
of a @emph{global} variable, as shown in the example.  GCC issues
a warning and otherwise ignores the @code{section} attribute in
uninitialized variable declarations.

You may only use the @code{section} attribute with a fully initialized
global definition because of the way linkers work.  The linker requires
each object be defined once, with the exception that uninitialized
variables tentatively go in the @code{common} (or @code{bss}) section
and can be multiply ``defined''.  You can force a variable to be
initialized with the @option{-fno-common} flag or the @code{nocommon}
attribute.

Some file formats do not support arbitrary sections so the @code{section}
attribute is not available on all platforms.
If you need to map the entire contents of a module to a particular
section, consider using the facilities of the linker instead.

@item shared
@cindex @code{shared} variable attribute
On Microsoft Windows, in addition to putting variable definitions in a named
section, the section can also be shared among all running copies of an
executable or DLL@.  For example, this small program defines shared data
by putting it in a named section @code{shared} and marking the section
shareable:

@smallexample
int foo __attribute__((section ("shared"), shared)) = 0;

int
main()
@{
  /* @r{Read and write foo.  All running
     copies see the same value.}  */
  return 0;
@}
@end smallexample

@noindent
You may only use the @code{shared} attribute along with @code{section}
attribute with a fully initialized global definition because of the way
linkers work.  See @code{section} attribute for more information.

The @code{shared} attribute is only available on Microsoft Windows@.

@item tls_model ("@var{tls_model}")
@cindex @code{tls_model} attribute
The @code{tls_model} attribute sets thread-local storage model
(@pxref{Thread-Local}) of a particular @code{__thread} variable,
overriding @option{-ftls-model=} command line switch on a per-variable
basis.
The @var{tls_model} argument should be one of @code{global-dynamic},
@code{local-dynamic}, @code{initial-exec} or @code{local-exec}.

Not all targets support this attribute.

@item unused
This attribute, attached to a variable, means that the variable is meant
to be possibly unused.  GCC will not produce a warning for this
variable.

@item used
This attribute, attached to a variable, means that the variable must be
emitted even if it appears that the variable is not referenced.

@item vector_size (@var{bytes})
This attribute specifies the vector size for the variable, measured in
bytes.  For example, the declaration:

@smallexample
int foo __attribute__ ((vector_size (16)));
@end smallexample

@noindent
causes the compiler to set the mode for @code{foo}, to be 16 bytes,
divided into @code{int} sized units.  Assuming a 32-bit int (a vector of
4 units of 4 bytes), the corresponding mode of @code{foo} will be V4SI@.

This attribute is only applicable to integral and float scalars,
although arrays, pointers, and function return values are allowed in
conjunction with this construct.

Aggregates with this attribute are invalid, even if they are of the same
size as a corresponding scalar.  For example, the declaration:

@smallexample
struct S @{ int a; @};
struct S  __attribute__ ((vector_size (16))) foo;
@end smallexample

@noindent
is invalid even if the size of the structure is the same as the size of
the @code{int}.

@item selectany
The @code{selectany} attribute causes an initialized global variable to
have link-once semantics.  When multiple definitions of the variable are
encountered by the linker, the first is selected and the remainder are
discarded.  Following usage by the Microsoft compiler, the linker is told
@emph{not} to warn about size or content differences of the multiple
definitions.

Although the primary usage of this attribute is for POD types, the
attribute can also be applied to global C++ objects that are initialized
by a constructor.  In this case, the static initialization and destruction
code for the object is emitted in each translation defining the object,
but the calls to the constructor and destructor are protected by a
link-once guard variable.

The @code{selectany} attribute is only available on Microsoft Windows
targets.  You can use @code{__declspec (selectany)} as a synonym for
@code{__attribute__ ((selectany))} for compatibility with other
compilers.

@item weak
The @code{weak} attribute is described in @xref{Function Attributes}.

@item dllimport
The @code{dllimport} attribute is described in @xref{Function Attributes}.

@item dllexport
The @code{dllexport} attribute is described in @xref{Function Attributes}.

@end table

@subsection M32R/D Variable Attributes

One attribute is currently defined for the M32R/D@.

@table @code
@item model (@var{model-name})
@cindex variable addressability on the M32R/D
Use this attribute on the M32R/D to set the addressability of an object.
The identifier @var{model-name} is one of @code{small}, @code{medium},
or @code{large}, representing each of the code models.

Small model objects live in the lower 16MB of memory (so that their
addresses can be loaded with the @code{ld24} instruction).

Medium and large model objects may live anywhere in the 32-bit address space
(the compiler will generate @code{seth/add3} instructions to load their
addresses).
@end table

@anchor{i386 Variable Attributes}
@subsection i386 Variable Attributes

Two attributes are currently defined for i386 configurations:
@code{ms_struct} and @code{gcc_struct}

@table @code
@item ms_struct
@itemx gcc_struct
@cindex @code{ms_struct} attribute
@cindex @code{gcc_struct} attribute

If @code{packed} is used on a structure, or if bit-fields are used
it may be that the Microsoft ABI packs them differently
than GCC would normally pack them.  Particularly when moving packed
data between functions compiled with GCC and the native Microsoft compiler
(either via function call or as data in a file), it may be necessary to access
either format.

Currently @option{-m[no-]ms-bitfields} is provided for the Microsoft Windows X86
compilers to match the native Microsoft compiler.

The Microsoft structure layout algorithm is fairly simple with the exception
of the bitfield packing:

The padding and alignment of members of structures and whether a bit field
can straddle a storage-unit boundary

@enumerate
@item Structure members are stored sequentially in the order in which they are
declared: the first member has the lowest memory address and the last member
the highest.

@item Every data object has an alignment-requirement. The alignment-requirement
for all data except structures, unions, and arrays is either the size of the
object or the current packing size (specified with either the aligned attribute
or the pack pragma), whichever is less. For structures,  unions, and arrays,
the alignment-requirement is the largest alignment-requirement of its members.
Every object is allocated an offset so that:

offset %  alignment-requirement == 0

@item Adjacent bit fields are packed into the same 1-, 2-, or 4-byte allocation
unit if the integral types are the same size and if the next bit field fits
into the current allocation unit without crossing the boundary imposed by the
common alignment requirements of the bit fields.
@end enumerate

Handling of zero-length bitfields:

MSVC interprets zero-length bitfields in the following ways:

@enumerate
@item If a zero-length bitfield is inserted between two bitfields that would
normally be coalesced, the bitfields will not be coalesced.

For example:

@smallexample
struct
 @{
   unsigned long bf_1 : 12;
   unsigned long : 0;
   unsigned long bf_2 : 12;
 @} t1;
@end smallexample

The size of @code{t1} would be 8 bytes with the zero-length bitfield.  If the
zero-length bitfield were removed, @code{t1}'s size would be 4 bytes.

@item If a zero-length bitfield is inserted after a bitfield, @code{foo}, and the
alignment of the zero-length bitfield is greater than the member that follows it,
@code{bar}, @code{bar} will be aligned as the type of the zero-length bitfield.

For example:

@smallexample
struct
 @{
   char foo : 4;
   short : 0;
   char bar;
 @} t2;

struct
 @{
   char foo : 4;
   short : 0;
   double bar;
 @} t3;
@end smallexample

For @code{t2}, @code{bar} will be placed at offset 2, rather than offset 1.
Accordingly, the size of @code{t2} will be 4.  For @code{t3}, the zero-length
bitfield will not affect the alignment of @code{bar} or, as a result, the size
of the structure.

Taking this into account, it is important to note the following:

@enumerate
@item If a zero-length bitfield follows a normal bitfield, the type of the
zero-length bitfield may affect the alignment of the structure as whole. For
example, @code{t2} has a size of 4 bytes, since the zero-length bitfield follows a
normal bitfield, and is of type short.

@item Even if a zero-length bitfield is not followed by a normal bitfield, it may
still affect the alignment of the structure:

@smallexample
struct
 @{
   char foo : 6;
   long : 0;
 @} t4;
@end smallexample

Here, @code{t4} will take up 4 bytes.
@end enumerate

@item Zero-length bitfields following non-bitfield members are ignored:

@smallexample
struct
 @{
   char foo;
   long : 0;
   char bar;
 @} t5;
@end smallexample

Here, @code{t5} will take up 2 bytes.
@end enumerate
@end table

@subsection PowerPC Variable Attributes

Three attributes currently are defined for PowerPC configurations:
@code{altivec}, @code{ms_struct} and @code{gcc_struct}.

For full documentation of the struct attributes please see the
documentation in the @xref{i386 Variable Attributes}, section.

For documentation of @code{altivec} attribute please see the
documentation in the @xref{PowerPC Type Attributes}, section.

@subsection Xstormy16 Variable Attributes

One attribute is currently defined for xstormy16 configurations:
@code{below100}

@table @code
@item below100
@cindex @code{below100} attribute

If a variable has the @code{below100} attribute (@code{BELOW100} is
allowed also), GCC will place the variable in the first 0x100 bytes of
memory and use special opcodes to access it.  Such variables will be
placed in either the @code{.bss_below100} section or the
@code{.data_below100} section.

@end table

@node Type Attributes
@section Specifying Attributes of Types
@cindex attribute of types
@cindex type attributes

The keyword @code{__attribute__} allows you to specify special
attributes of @code{struct} and @code{union} types when you define
such types.  This keyword is followed by an attribute specification
inside double parentheses.  Seven attributes are currently defined for
types: @code{aligned}, @code{packed}, @code{transparent_union},
@code{unused}, @code{deprecated}, @code{visibility}, and
@code{may_alias}.  Other attributes are defined for functions
(@pxref{Function Attributes}) and for variables (@pxref{Variable
Attributes}).

You may also specify any one of these attributes with @samp{__}
preceding and following its keyword.  This allows you to use these
attributes in header files without being concerned about a possible
macro of the same name.  For example, you may use @code{__aligned__}
instead of @code{aligned}.

You may specify type attributes either in a @code{typedef} declaration
or in an enum, struct or union type declaration or definition.

For an enum, struct or union type, you may specify attributes either
between the enum, struct or union tag and the name of the type, or
just past the closing curly brace of the @emph{definition}.  The
former syntax is preferred.

@xref{Attribute Syntax}, for details of the exact syntax for using
attributes.

@table @code
@cindex @code{aligned} attribute
@item aligned (@var{alignment})
This attribute specifies a minimum alignment (in bytes) for variables
of the specified type.  For example, the declarations:

@smallexample
struct S @{ short f[3]; @} __attribute__ ((aligned (8)));
typedef int more_aligned_int __attribute__ ((aligned (8)));
@end smallexample

@noindent
force the compiler to insure (as far as it can) that each variable whose
type is @code{struct S} or @code{more_aligned_int} will be allocated and
aligned @emph{at least} on a 8-byte boundary.  On a SPARC, having all
variables of type @code{struct S} aligned to 8-byte boundaries allows
the compiler to use the @code{ldd} and @code{std} (doubleword load and
store) instructions when copying one variable of type @code{struct S} to
another, thus improving run-time efficiency.

Note that the alignment of any given @code{struct} or @code{union} type
is required by the ISO C standard to be at least a perfect multiple of
the lowest common multiple of the alignments of all of the members of
the @code{struct} or @code{union} in question.  This means that you @emph{can}
effectively adjust the alignment of a @code{struct} or @code{union}
type by attaching an @code{aligned} attribute to any one of the members
of such a type, but the notation illustrated in the example above is a
more obvious, intuitive, and readable way to request the compiler to
adjust the alignment of an entire @code{struct} or @code{union} type.

As in the preceding example, you can explicitly specify the alignment
(in bytes) that you wish the compiler to use for a given @code{struct}
or @code{union} type.  Alternatively, you can leave out the alignment factor
and just ask the compiler to align a type to the maximum
useful alignment for the target machine you are compiling for.  For
example, you could write:

@smallexample
struct S @{ short f[3]; @} __attribute__ ((aligned));
@end smallexample

Whenever you leave out the alignment factor in an @code{aligned}
attribute specification, the compiler automatically sets the alignment
for the type to the largest alignment which is ever used for any data
type on the target machine you are compiling for.  Doing this can often
make copy operations more efficient, because the compiler can use
whatever instructions copy the biggest chunks of memory when performing
copies to or from the variables which have types that you have aligned
this way.

In the example above, if the size of each @code{short} is 2 bytes, then
the size of the entire @code{struct S} type is 6 bytes.  The smallest
power of two which is greater than or equal to that is 8, so the
compiler sets the alignment for the entire @code{struct S} type to 8
bytes.

Note that although you can ask the compiler to select a time-efficient
alignment for a given type and then declare only individual stand-alone
objects of that type, the compiler's ability to select a time-efficient
alignment is primarily useful only when you plan to create arrays of
variables having the relevant (efficiently aligned) type.  If you
declare or use arrays of variables of an efficiently-aligned type, then
it is likely that your program will also be doing pointer arithmetic (or
subscripting, which amounts to the same thing) on pointers to the
relevant type, and the code that the compiler generates for these
pointer arithmetic operations will often be more efficient for
efficiently-aligned types than for other types.

The @code{aligned} attribute can only increase the alignment; but you
can decrease it by specifying @code{packed} as well.  See below.

Note that the effectiveness of @code{aligned} attributes may be limited
by inherent limitations in your linker.  On many systems, the linker is
only able to arrange for variables to be aligned up to a certain maximum
alignment.  (For some linkers, the maximum supported alignment may
be very very small.)  If your linker is only able to align variables
up to a maximum of 8 byte alignment, then specifying @code{aligned(16)}
in an @code{__attribute__} will still only provide you with 8 byte
alignment.  See your linker documentation for further information.

@item packed
This attribute, attached to @code{struct} or @code{union} type
definition, specifies that each member (other than zero-width bitfields)
of the structure or union is placed to minimize the memory required.  When
attached to an @code{enum} definition, it indicates that the smallest
integral type should be used.

@opindex fshort-enums
Specifying this attribute for @code{struct} and @code{union} types is
equivalent to specifying the @code{packed} attribute on each of the
structure or union members.  Specifying the @option{-fshort-enums}
flag on the line is equivalent to specifying the @code{packed}
attribute on all @code{enum} definitions.

In the following example @code{struct my_packed_struct}'s members are
packed closely together, but the internal layout of its @code{s} member
is not packed---to do that, @code{struct my_unpacked_struct} would need to
be packed too.

@smallexample
struct my_unpacked_struct
 @{
    char c;
    int i;
 @};

struct __attribute__ ((__packed__)) my_packed_struct
  @{
     char c;
     int  i;
     struct my_unpacked_struct s;
  @};
@end smallexample

You may only specify this attribute on the definition of a @code{enum},
@code{struct} or @code{union}, not on a @code{typedef} which does not
also define the enumerated type, structure or union.

@item transparent_union
This attribute, attached to a @code{union} type definition, indicates
that any function parameter having that union type causes calls to that
function to be treated in a special way.

First, the argument corresponding to a transparent union type can be of
any type in the union; no cast is required.  Also, if the union contains
a pointer type, the corresponding argument can be a null pointer
constant or a void pointer expression; and if the union contains a void
pointer type, the corresponding argument can be any pointer expression.
If the union member type is a pointer, qualifiers like @code{const} on
the referenced type must be respected, just as with normal pointer
conversions.

Second, the argument is passed to the function using the calling
conventions of the first member of the transparent union, not the calling
conventions of the union itself.  All members of the union must have the
same machine representation; this is necessary for this argument passing
to work properly.

Transparent unions are designed for library functions that have multiple
interfaces for compatibility reasons.  For example, suppose the
@code{wait} function must accept either a value of type @code{int *} to
comply with Posix, or a value of type @code{union wait *} to comply with
the 4.1BSD interface.  If @code{wait}'s parameter were @code{void *},
@code{wait} would accept both kinds of arguments, but it would also
accept any other pointer type and this would make argument type checking
less useful.  Instead, @code{<sys/wait.h>} might define the interface
as follows:

@smallexample
typedef union
  @{
    int *__ip;
    union wait *__up;
  @} wait_status_ptr_t __attribute__ ((__transparent_union__));

pid_t wait (wait_status_ptr_t);
@end smallexample

This interface allows either @code{int *} or @code{union wait *}
arguments to be passed, using the @code{int *} calling convention.
The program can call @code{wait} with arguments of either type:

@smallexample
int w1 () @{ int w; return wait (&w); @}
int w2 () @{ union wait w; return wait (&w); @}
@end smallexample

With this interface, @code{wait}'s implementation might look like this:

@smallexample
pid_t wait (wait_status_ptr_t p)
@{
  return waitpid (-1, p.__ip, 0);
@}
@end smallexample

@item unused
When attached to a type (including a @code{union} or a @code{struct}),
this attribute means that variables of that type are meant to appear
possibly unused.  GCC will not produce a warning for any variables of
that type, even if the variable appears to do nothing.  This is often
the case with lock or thread classes, which are usually defined and then
not referenced, but contain constructors and destructors that have
nontrivial bookkeeping functions.

@item deprecated
The @code{deprecated} attribute results in a warning if the type
is used anywhere in the source file.  This is useful when identifying
types that are expected to be removed in a future version of a program.
If possible, the warning also includes the location of the declaration
of the deprecated type, to enable users to easily find further
information about why the type is deprecated, or what they should do
instead.  Note that the warnings only occur for uses and then only
if the type is being applied to an identifier that itself is not being
declared as deprecated.

@smallexample
typedef int T1 __attribute__ ((deprecated));
T1 x;
typedef T1 T2;
T2 y;
typedef T1 T3 __attribute__ ((deprecated));
T3 z __attribute__ ((deprecated));
@end smallexample

results in a warning on line 2 and 3 but not lines 4, 5, or 6.  No
warning is issued for line 4 because T2 is not explicitly
deprecated.  Line 5 has no warning because T3 is explicitly
deprecated.  Similarly for line 6.

The @code{deprecated} attribute can also be used for functions and
variables (@pxref{Function Attributes}, @pxref{Variable Attributes}.)

@item may_alias
Accesses to objects with types with this attribute are not subjected to
type-based alias analysis, but are instead assumed to be able to alias
any other type of objects, just like the @code{char} type.  See
@option{-fstrict-aliasing} for more information on aliasing issues.

Example of use:

@smallexample
typedef short __attribute__((__may_alias__)) short_a;

int
main (void)
@{
  int a = 0x12345678;
  short_a *b = (short_a *) &a;

  b[1] = 0;

  if (a == 0x12345678)
    abort();

  exit(0);
@}
@end smallexample

If you replaced @code{short_a} with @code{short} in the variable
declaration, the above program would abort when compiled with
@option{-fstrict-aliasing}, which is on by default at @option{-O2} or
above in recent GCC versions.

@item visibility
In C++, attribute visibility (@pxref{Function Attributes}) can also be
applied to class, struct, union and enum types.  Unlike other type
attributes, the attribute must appear between the initial keyword and
the name of the type; it cannot appear after the body of the type.

Note that the type visibility is applied to vague linkage entities
associated with the class (vtable, typeinfo node, etc.).  In
particular, if a class is thrown as an exception in one shared object
and caught in another, the class must have default visibility.
Otherwise the two shared objects will be unable to use the same
typeinfo node and exception handling will break.

@subsection ARM Type Attributes

On those ARM targets that support @code{dllimport} (such as Symbian
OS), you can use the @code{notshared} attribute to indicate that the
virtual table and other similar data for a class should not be
exported from a DLL@.  For example:

@smallexample
class __declspec(notshared) C @{
public:
  __declspec(dllimport) C();
  virtual void f();
@}

__declspec(dllexport)
C::C() @{@}
@end smallexample

In this code, @code{C::C} is exported from the current DLL, but the
virtual table for @code{C} is not exported.  (You can use
@code{__attribute__} instead of @code{__declspec} if you prefer, but
most Symbian OS code uses @code{__declspec}.)

@anchor{i386 Type Attributes}
@subsection i386 Type Attributes

Two attributes are currently defined for i386 configurations:
@code{ms_struct} and @code{gcc_struct}

@item ms_struct
@itemx gcc_struct
@cindex @code{ms_struct}
@cindex @code{gcc_struct}

If @code{packed} is used on a structure, or if bit-fields are used
it may be that the Microsoft ABI packs them differently
than GCC would normally pack them.  Particularly when moving packed
data between functions compiled with GCC and the native Microsoft compiler
(either via function call or as data in a file), it may be necessary to access
either format.

Currently @option{-m[no-]ms-bitfields} is provided for the Microsoft Windows X86
compilers to match the native Microsoft compiler.
@end table

To specify multiple attributes, separate them by commas within the
double parentheses: for example, @samp{__attribute__ ((aligned (16),
packed))}.

@anchor{PowerPC Type Attributes}
@subsection PowerPC Type Attributes

Three attributes currently are defined for PowerPC configurations:
@code{altivec}, @code{ms_struct} and @code{gcc_struct}.

For full documentation of the struct attributes please see the
documentation in the @xref{i386 Type Attributes}, section.

The @code{altivec} attribute allows one to declare AltiVec vector data
types supported by the AltiVec Programming Interface Manual.  The
attribute requires an argument to specify one of three vector types:
@code{vector__}, @code{pixel__} (always followed by unsigned short),
and @code{bool__} (always followed by unsigned).

@smallexample
__attribute__((altivec(vector__)))
__attribute__((altivec(pixel__))) unsigned short
__attribute__((altivec(bool__))) unsigned
@end smallexample

These attributes mainly are intended to support the @code{__vector},
@code{__pixel}, and @code{__bool} AltiVec keywords.

@node Inline
@section An Inline Function is As Fast As a Macro
@cindex inline functions
@cindex integrating function code
@cindex open coding
@cindex macros, inline alternative

By declaring a function @code{inline}, you can direct GCC to
integrate that function's code into the code for its callers.  This
makes execution faster by eliminating the function-call overhead; in
addition, if any of the actual argument values are constant, their known
values may permit simplifications at compile time so that not all of the
inline function's code needs to be included.  The effect on code size is
less predictable; object code may be larger or smaller with function
inlining, depending on the particular case.  Inlining of functions is an
optimization and it really ``works'' only in optimizing compilation.  If
you don't use @option{-O}, no function is really inline.

Inline functions are included in the ISO C99 standard, but there are
currently substantial differences between what GCC implements and what
the ISO C99 standard requires.  GCC will fully support C99 inline
functions in version 4.3.  The traditional GCC handling of inline
functions will still be available with @option{-std=gnu89},
@option{-fgnu89-inline} or when @code{gnu_inline} attribute is present
on all inline declarations.  The preprocessor macros
@code{__GNUC_GNU_INLINE__} and @code{__GNUC_STDC_INLINE__} may be used
to determine the handling of @code{inline} during a particular
compilation (@pxref{Common Predefined Macros,,,cpp,The C
Preprocessor}).

To declare a function inline, use the @code{inline} keyword in its
declaration, like this:

@smallexample
inline int
inc (int *a)
@{
  (*a)++;
@}
@end smallexample

(If you are writing a header file to be included in ISO C programs, write
@code{__inline__} instead of @code{inline}.  @xref{Alternate Keywords}.)
You can also make all ``simple enough'' functions inline with the option
@option{-finline-functions}.

@opindex Winline
Note that certain usages in a function definition can make it unsuitable
for inline substitution.  Among these usages are: use of varargs, use of
alloca, use of variable sized data types (@pxref{Variable Length}),
use of computed goto (@pxref{Labels as Values}), use of nonlocal goto,
and nested functions (@pxref{Nested Functions}).  Using @option{-Winline}
will warn when a function marked @code{inline} could not be substituted,
and will give the reason for the failure.

Note that in C and Objective-C, unlike C++, the @code{inline} keyword
does not affect the linkage of the function.

@cindex automatic @code{inline} for C++ member fns
@cindex @code{inline} automatic for C++ member fns
@cindex member fns, automatically @code{inline}
@cindex C++ member fns, automatically @code{inline}
@opindex fno-default-inline
GCC automatically inlines member functions defined within the class
body of C++ programs even if they are not explicitly declared
@code{inline}.  (You can override this with @option{-fno-default-inline};
@pxref{C++ Dialect Options,,Options Controlling C++ Dialect}.)

@cindex inline functions, omission of
@opindex fkeep-inline-functions
When a function is both inline and @code{static}, if all calls to the
function are integrated into the caller, and the function's address is
never used, then the function's own assembler code is never referenced.
In this case, GCC does not actually output assembler code for the
function, unless you specify the option @option{-fkeep-inline-functions}.
Some calls cannot be integrated for various reasons (in particular,
calls that precede the function's definition cannot be integrated, and
neither can recursive calls within the definition).  If there is a
nonintegrated call, then the function is compiled to assembler code as
usual.  The function must also be compiled as usual if the program
refers to its address, because that can't be inlined.

@cindex non-static inline function
When an inline function is not @code{static}, then the compiler must assume
that there may be calls from other source files; since a global symbol can
be defined only once in any program, the function must not be defined in
the other source files, so the calls therein cannot be integrated.
Therefore, a non-@code{static} inline function is always compiled on its
own in the usual fashion.

If you specify both @code{inline} and @code{extern} in the function
definition, then the definition is used only for inlining.  In no case
is the function compiled on its own, not even if you refer to its
address explicitly.  Such an address becomes an external reference, as
if you had only declared the function, and had not defined it.

This combination of @code{inline} and @code{extern} has almost the
effect of a macro.  The way to use it is to put a function definition in
a header file with these keywords, and put another copy of the
definition (lacking @code{inline} and @code{extern}) in a library file.
The definition in the header file will cause most calls to the function
to be inlined.  If any uses of the function remain, they will refer to
the single copy in the library.

Since GCC 4.3 will implement ISO C99 semantics for
inline functions, it is simplest to use @code{static inline} only
to guarantee compatibility.  (The
existing semantics will remain available when @option{-std=gnu89} is
specified, but eventually the default will be @option{-std=gnu99};
that will implement the C99 semantics, though it does not do so in
versions of GCC before 4.3.  After the default changes, the existing
semantics will still be available via the @option{-fgnu89-inline}
option or the @code{gnu_inline} function attribute.)

GCC does not inline any functions when not optimizing unless you specify
the @samp{always_inline} attribute for the function, like this:

@smallexample
/* @r{Prototype.}  */
inline void foo (const char) __attribute__((always_inline));
@end smallexample

@node Extended Asm
@section Assembler Instructions with C Expression Operands
@cindex extended @code{asm}
@cindex @code{asm} expressions
@cindex assembler instructions
@cindex registers

In an assembler instruction using @code{asm}, you can specify the
operands of the instruction using C expressions.  This means you need not
guess which registers or memory locations will contain the data you want
to use.

You must specify an assembler instruction template much like what
appears in a machine description, plus an operand constraint string for
each operand.

For example, here is how to use the 68881's @code{fsinx} instruction:

@smallexample
asm ("fsinx %1,%0" : "=f" (result) : "f" (angle));
@end smallexample

@noindent
Here @code{angle} is the C expression for the input operand while
@code{result} is that of the output operand.  Each has @samp{"f"} as its
operand constraint, saying that a floating point register is required.
The @samp{=} in @samp{=f} indicates that the operand is an output; all
output operands' constraints must use @samp{=}.  The constraints use the
same language used in the machine description (@pxref{Constraints}).

Each operand is described by an operand-constraint string followed by
the C expression in parentheses.  A colon separates the assembler
template from the first output operand and another separates the last
output operand from the first input, if any.  Commas separate the
operands within each group.  The total number of operands is currently
limited to 30; this limitation may be lifted in some future version of
GCC@.

If there are no output operands but there are input operands, you must
place two consecutive colons surrounding the place where the output
operands would go.

As of GCC version 3.1, it is also possible to specify input and output
operands using symbolic names which can be referenced within the
assembler code.  These names are specified inside square brackets
preceding the constraint string, and can be referenced inside the
assembler code using @code{%[@var{name}]} instead of a percentage sign
followed by the operand number.  Using named operands the above example
could look like:

@smallexample
asm ("fsinx %[angle],%[output]"
     : [output] "=f" (result)
     : [angle] "f" (angle));
@end smallexample

@noindent
Note that the symbolic operand names have no relation whatsoever to
other C identifiers.  You may use any name you like, even those of
existing C symbols, but you must ensure that no two operands within the same
assembler construct use the same symbolic name.

Output operand expressions must be lvalues; the compiler can check this.
The input operands need not be lvalues.  The compiler cannot check
whether the operands have data types that are reasonable for the
instruction being executed.  It does not parse the assembler instruction
template and does not know what it means or even whether it is valid
assembler input.  The extended @code{asm} feature is most often used for
machine instructions the compiler itself does not know exist.  If
the output expression cannot be directly addressed (for example, it is a
bit-field), your constraint must allow a register.  In that case, GCC
will use the register as the output of the @code{asm}, and then store
that register into the output.

The ordinary output operands must be write-only; GCC will assume that
the values in these operands before the instruction are dead and need
not be generated.  Extended asm supports input-output or read-write
operands.  Use the constraint character @samp{+} to indicate such an
operand and list it with the output operands.  You should only use
read-write operands when the constraints for the operand (or the
operand in which only some of the bits are to be changed) allow a
register.

You may, as an alternative, logically split its function into two
separate operands, one input operand and one write-only output
operand.  The connection between them is expressed by constraints
which say they need to be in the same location when the instruction
executes.  You can use the same C expression for both operands, or
different expressions.  For example, here we write the (fictitious)
@samp{combine} instruction with @code{bar} as its read-only source
operand and @code{foo} as its read-write destination:

@smallexample
asm ("combine %2,%0" : "=r" (foo) : "0" (foo), "g" (bar));
@end smallexample

@noindent
The constraint @samp{"0"} for operand 1 says that it must occupy the
same location as operand 0.  A number in constraint is allowed only in
an input operand and it must refer to an output operand.

Only a number in the constraint can guarantee that one operand will be in
the same place as another.  The mere fact that @code{foo} is the value
of both operands is not enough to guarantee that they will be in the
same place in the generated assembler code.  The following would not
work reliably:

@smallexample
asm ("combine %2,%0" : "=r" (foo) : "r" (foo), "g" (bar));
@end smallexample

Various optimizations or reloading could cause operands 0 and 1 to be in
different registers; GCC knows no reason not to do so.  For example, the
compiler might find a copy of the value of @code{foo} in one register and
use it for operand 1, but generate the output operand 0 in a different
register (copying it afterward to @code{foo}'s own address).  Of course,
since the register for operand 1 is not even mentioned in the assembler
code, the result will not work, but GCC can't tell that.

As of GCC version 3.1, one may write @code{[@var{name}]} instead of
the operand number for a matching constraint.  For example:

@smallexample
asm ("cmoveq %1,%2,%[result]"
     : [result] "=r"(result)
     : "r" (test), "r"(new), "[result]"(old));
@end smallexample

Sometimes you need to make an @code{asm} operand be a specific register,
but there's no matching constraint letter for that register @emph{by
itself}.  To force the operand into that register, use a local variable
for the operand and specify the register in the variable declaration.
@xref{Explicit Reg Vars}.  Then for the @code{asm} operand, use any
register constraint letter that matches the register:

@smallexample
register int *p1 asm ("r0") = @dots{};
register int *p2 asm ("r1") = @dots{};
register int *result asm ("r0");
asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));
@end smallexample

@anchor{Example of asm with clobbered asm reg}
In the above example, beware that a register that is call-clobbered by
the target ABI will be overwritten by any function call in the
assignment, including library calls for arithmetic operators.
Assuming it is a call-clobbered register, this may happen to @code{r0}
above by the assignment to @code{p2}.  If you have to use such a
register, use temporary variables for expressions between the register
assignment and use:

@smallexample
int t1 = @dots{};
register int *p1 asm ("r0") = @dots{};
register int *p2 asm ("r1") = t1;
register int *result asm ("r0");
asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));
@end smallexample

Some instructions clobber specific hard registers.  To describe this,
write a third colon after the input operands, followed by the names of
the clobbered hard registers (given as strings).  Here is a realistic
example for the VAX:

@smallexample
asm volatile ("movc3 %0,%1,%2"
              : /* @r{no outputs} */
              : "g" (from), "g" (to), "g" (count)
              : "r0", "r1", "r2", "r3", "r4", "r5");
@end smallexample

You may not write a clobber description in a way that overlaps with an
input or output operand.  For example, you may not have an operand
describing a register class with one member if you mention that register
in the clobber list.  Variables declared to live in specific registers
(@pxref{Explicit Reg Vars}), and used as asm input or output operands must
have no part mentioned in the clobber description.
There is no way for you to specify that an input
operand is modified without also specifying it as an output
operand.  Note that if all the output operands you specify are for this
purpose (and hence unused), you will then also need to specify
@code{volatile} for the @code{asm} construct, as described below, to
prevent GCC from deleting the @code{asm} statement as unused.

If you refer to a particular hardware register from the assembler code,
you will probably have to list the register after the third colon to
tell the compiler the register's value is modified.  In some assemblers,
the register names begin with @samp{%}; to produce one @samp{%} in the
assembler code, you must write @samp{%%} in the input.

If your assembler instruction can alter the condition code register, add
@samp{cc} to the list of clobbered registers.  GCC on some machines
represents the condition codes as a specific hardware register;
@samp{cc} serves to name this register.  On other machines, the
condition code is handled differently, and specifying @samp{cc} has no
effect.  But it is valid no matter what the machine.

If your assembler instructions access memory in an unpredictable
fashion, add @samp{memory} to the list of clobbered registers.  This
will cause GCC to not keep memory values cached in registers across the
assembler instruction and not optimize stores or loads to that memory.
You will also want to add the @code{volatile} keyword if the memory
affected is not listed in the inputs or outputs of the @code{asm}, as
the @samp{memory} clobber does not count as a side-effect of the
@code{asm}.  If you know how large the accessed memory is, you can add
it as input or output but if this is not known, you should add
@samp{memory}.  As an example, if you access ten bytes of a string, you
can use a memory input like:

@smallexample
@{"m"( (@{ struct @{ char x[10]; @} *p = (void *)ptr ; *p; @}) )@}.
@end smallexample

Note that in the following example the memory input is necessary,
otherwise GCC might optimize the store to @code{x} away:
@smallexample
int foo ()
@{
  int x = 42;
  int *y = &x;
  int result;
  asm ("magic stuff accessing an 'int' pointed to by '%1'"
        "=&d" (r) : "a" (y), "m" (*y));
  return result;
@}
@end smallexample

You can put multiple assembler instructions together in a single
@code{asm} template, separated by the characters normally used in assembly
code for the system.  A combination that works in most places is a newline
to break the line, plus a tab character to move to the instruction field
(written as @samp{\n\t}).  Sometimes semicolons can be used, if the
assembler allows semicolons as a line-breaking character.  Note that some
assembler dialects use semicolons to start a comment.
The input operands are guaranteed not to use any of the clobbered
registers, and neither will the output operands' addresses, so you can
read and write the clobbered registers as many times as you like.  Here
is an example of multiple instructions in a template; it assumes the
subroutine @code{_foo} accepts arguments in registers 9 and 10:

@smallexample
asm ("movl %0,r9\n\tmovl %1,r10\n\tcall _foo"
     : /* no outputs */
     : "g" (from), "g" (to)
     : "r9", "r10");
@end smallexample

Unless an output operand has the @samp{&} constraint modifier, GCC
may allocate it in the same register as an unrelated input operand, on
the assumption the inputs are consumed before the outputs are produced.
This assumption may be false if the assembler code actually consists of
more than one instruction.  In such a case, use @samp{&} for each output
operand that may not overlap an input.  @xref{Modifiers}.

If you want to test the condition code produced by an assembler
instruction, you must include a branch and a label in the @code{asm}
construct, as follows:

@smallexample
asm ("clr %0\n\tfrob %1\n\tbeq 0f\n\tmov #1,%0\n0:"
     : "g" (result)
     : "g" (input));
@end smallexample

@noindent
This assumes your assembler supports local labels, as the GNU assembler
and most Unix assemblers do.

Speaking of labels, jumps from one @code{asm} to another are not
supported.  The compiler's optimizers do not know about these jumps, and
therefore they cannot take account of them when deciding how to
optimize.

@cindex macros containing @code{asm}
Usually the most convenient way to use these @code{asm} instructions is to
encapsulate them in macros that look like functions.  For example,

@smallexample
#define sin(x)       \
(@{ double __value, __arg = (x);   \
   asm ("fsinx %1,%0": "=f" (__value): "f" (__arg));  \
   __value; @})
@end smallexample

@noindent
Here the variable @code{__arg} is used to make sure that the instruction
operates on a proper @code{double} value, and to accept only those
arguments @code{x} which can convert automatically to a @code{double}.

Another way to make sure the instruction operates on the correct data
type is to use a cast in the @code{asm}.  This is different from using a
variable @code{__arg} in that it converts more different types.  For
example, if the desired type were @code{int}, casting the argument to
@code{int} would accept a pointer with no complaint, while assigning the
argument to an @code{int} variable named @code{__arg} would warn about
using a pointer unless the caller explicitly casts it.

If an @code{asm} has output operands, GCC assumes for optimization
purposes the instruction has no side effects except to change the output
operands.  This does not mean instructions with a side effect cannot be
used, but you must be careful, because the compiler may eliminate them
if the output operands aren't used, or move them out of loops, or
replace two with one if they constitute a common subexpression.  Also,
if your instruction does have a side effect on a variable that otherwise
appears not to change, the old value of the variable may be reused later
if it happens to be found in a register.

You can prevent an @code{asm} instruction from being deleted
by writing the keyword @code{volatile} after
the @code{asm}.  For example:

@smallexample
#define get_and_set_priority(new)              \
(@{ int __old;                                  \
   asm volatile ("get_and_set_priority %0, %1" \
                 : "=g" (__old) : "g" (new));  \
   __old; @})
@end smallexample

@noindent
The @code{volatile} keyword indicates that the instruction has
important side-effects.  GCC will not delete a volatile @code{asm} if
it is reachable.  (The instruction can still be deleted if GCC can
prove that control-flow will never reach the location of the
instruction.)  Note that even a volatile @code{asm} instruction
can be moved relative to other code, including across jump
instructions.  For example, on many targets there is a system
register which can be set to control the rounding mode of
floating point operations.  You might try
setting it with a volatile @code{asm}, like this PowerPC example:

@smallexample
       asm volatile("mtfsf 255,%0" : : "f" (fpenv));
       sum = x + y;
@end smallexample

@noindent
This will not work reliably, as the compiler may move the addition back
before the volatile @code{asm}.  To make it work you need to add an
artificial dependency to the @code{asm} referencing a variable in the code
you don't want moved, for example:

@smallexample
    asm volatile ("mtfsf 255,%1" : "=X"(sum): "f"(fpenv));
    sum = x + y;
@end smallexample

Similarly, you can't expect a
sequence of volatile @code{asm} instructions to remain perfectly
consecutive.  If you want consecutive output, use a single @code{asm}.
Also, GCC will perform some optimizations across a volatile @code{asm}
instruction; GCC does not ``forget everything'' when it encounters
a volatile @code{asm} instruction the way some other compilers do.

An @code{asm} instruction without any output operands will be treated
identically to a volatile @code{asm} instruction.

It is a natural idea to look for a way to give access to the condition
code left by the assembler instruction.  However, when we attempted to
implement this, we found no way to make it work reliably.  The problem
is that output operands might need reloading, which would result in
additional following ``store'' instructions.  On most machines, these
instructions would alter the condition code before there was time to
test it.  This problem doesn't arise for ordinary ``test'' and
``compare'' instructions because they don't have any output operands.

For reasons similar to those described above, it is not possible to give
an assembler instruction access to the condition code left by previous
instructions.

If you are writing a header file that should be includable in ISO C
programs, write @code{__asm__} instead of @code{asm}.  @xref{Alternate
Keywords}.

@subsection Size of an @code{asm}

Some targets require that GCC track the size of each instruction used in
order to generate correct code.  Because the final length of an
@code{asm} is only known by the assembler, GCC must make an estimate as
to how big it will be.  The estimate is formed by counting the number of
statements in the pattern of the @code{asm} and multiplying that by the
length of the longest instruction on that processor.  Statements in the
@code{asm} are identified by newline characters and whatever statement
separator characters are supported by the assembler; on most processors
this is the `@code{;}' character.

Normally, GCC's estimate is perfectly adequate to ensure that correct
code is generated, but it is possible to confuse the compiler if you use
pseudo instructions or assembler macros that expand into multiple real
instructions or if you use assembler directives that expand to more
space in the object file than would be needed for a single instruction.
If this happens then the assembler will produce a diagnostic saying that
a label is unreachable.

@subsection i386 floating point asm operands

There are several rules on the usage of stack-like regs in
asm_operands insns.  These rules apply only to the operands that are
stack-like regs:

@enumerate
@item
Given a set of input regs that die in an asm_operands, it is
necessary to know which are implicitly popped by the asm, and
which must be explicitly popped by gcc.

An input reg that is implicitly popped by the asm must be
explicitly clobbered, unless it is constrained to match an
output operand.

@item
For any input reg that is implicitly popped by an asm, it is
necessary to know how to adjust the stack to compensate for the pop.
If any non-popped input is closer to the top of the reg-stack than
the implicitly popped reg, it would not be possible to know what the
stack looked like---it's not clear how the rest of the stack ``slides
up''.

All implicitly popped input regs must be closer to the top of
the reg-stack than any input that is not implicitly popped.

It is possible that if an input dies in an insn, reload might
use the input reg for an output reload.  Consider this example:

@smallexample
asm ("foo" : "=t" (a) : "f" (b));
@end smallexample

This asm says that input B is not popped by the asm, and that
the asm pushes a result onto the reg-stack, i.e., the stack is one
deeper after the asm than it was before.  But, it is possible that
reload will think that it can use the same reg for both the input and
the output, if input B dies in this insn.

If any input operand uses the @code{f} constraint, all output reg
constraints must use the @code{&} earlyclobber.

The asm above would be written as

@smallexample
asm ("foo" : "=&t" (a) : "f" (b));
@end smallexample

@item
Some operands need to be in particular places on the stack.  All
output operands fall in this category---there is no other way to
know which regs the outputs appear in unless the user indicates
this in the constraints.

Output operands must specifically indicate which reg an output
appears in after an asm.  @code{=f} is not allowed: the operand
constraints must select a class with a single reg.

@item
Output operands may not be ``inserted'' between existing stack regs.
Since no 387 opcode uses a read/write operand, all output operands
are dead before the asm_operands, and are pushed by the asm_operands.
It makes no sense to push anywhere but the top of the reg-stack.

Output operands must start at the top of the reg-stack: output
operands may not ``skip'' a reg.

@item
Some asm statements may need extra stack space for internal
calculations.  This can be guaranteed by clobbering stack registers
unrelated to the inputs and outputs.

@end enumerate

Here are a couple of reasonable asms to want to write.  This asm
takes one input, which is internally popped, and produces two outputs.

@smallexample
asm ("fsincos" : "=t" (cos), "=u" (sin) : "0" (inp));
@end smallexample

This asm takes two inputs, which are popped by the @code{fyl2xp1} opcode,
and replaces them with one output.  The user must code the @code{st(1)}
clobber for reg-stack.c to know that @code{fyl2xp1} pops both inputs.

@smallexample
asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)");
@end smallexample

@include md.texi

@node Asm Labels
@section Controlling Names Used in Assembler Code
@cindex assembler names for identifiers
@cindex names used in assembler code
@cindex identifiers, names in assembler code

You can specify the name to be used in the assembler code for a C
function or variable by writing the @code{asm} (or @code{__asm__})
keyword after the declarator as follows:

@smallexample
int foo asm ("myfoo") = 2;
@end smallexample

@noindent
This specifies that the name to be used for the variable @code{foo} in
the assembler code should be @samp{myfoo} rather than the usual
@samp{_foo}.

On systems where an underscore is normally prepended to the name of a C
function or variable, this feature allows you to define names for the
linker that do not start with an underscore.

It does not make sense to use this feature with a non-static local
variable since such variables do not have assembler names.  If you are
trying to put the variable in a particular register, see @ref{Explicit
Reg Vars}.  GCC presently accepts such code with a warning, but will
probably be changed to issue an error, rather than a warning, in the
future.

You cannot use @code{asm} in this way in a function @emph{definition}; but
you can get the same effect by writing a declaration for the function
before its definition and putting @code{asm} there, like this:

@smallexample
extern func () asm ("FUNC");

func (x, y)
     int x, y;
/* @r{@dots{}} */
@end smallexample

It is up to you to make sure that the assembler names you choose do not
conflict with any other assembler symbols.  Also, you must not use a
register name; that would produce completely invalid assembler code.  GCC
does not as yet have the ability to store static variables in registers.
Perhaps that will be added.

@node Explicit Reg Vars
@section Variables in Specified Registers
@cindex explicit register variables
@cindex variables in specified registers
@cindex specified registers
@cindex registers, global allocation

GNU C allows you to put a few global variables into specified hardware
registers.  You can also specify the register in which an ordinary
register variable should be allocated.

@itemize @bullet
@item
Global register variables reserve registers throughout the program.
This may be useful in programs such as programming language
interpreters which have a couple of global variables that are accessed
very often.

@item
Local register variables in specific registers do not reserve the
registers, except at the point where they are used as input or output
operands in an @code{asm} statement and the @code{asm} statement itself is
not deleted.  The compiler's data flow analysis is capable of determining
where the specified registers contain live values, and where they are
available for other uses.  Stores into local register variables may be deleted
when they appear to be dead according to dataflow analysis.  References
to local register variables may be deleted or moved or simplified.

These local variables are sometimes convenient for use with the extended
@code{asm} feature (@pxref{Extended Asm}), if you want to write one
output of the assembler instruction directly into a particular register.
(This will work provided the register you specify fits the constraints
specified for that operand in the @code{asm}.)
@end itemize

@menu
* Global Reg Vars::
* Local Reg Vars::
@end menu

@node Global Reg Vars
@subsection Defining Global Register Variables
@cindex global register variables
@cindex registers, global variables in

You can define a global register variable in GNU C like this:

@smallexample
register int *foo asm ("a5");
@end smallexample

@noindent
Here @code{a5} is the name of the register which should be used.  Choose a
register which is normally saved and restored by function calls on your
machine, so that library routines will not clobber it.

Naturally the register name is cpu-dependent, so you would need to
conditionalize your program according to cpu type.  The register
@code{a5} would be a good choice on a 68000 for a variable of pointer
type.  On machines with register windows, be sure to choose a ``global''
register that is not affected magically by the function call mechanism.

In addition, operating systems on one type of cpu may differ in how they
name the registers; then you would need additional conditionals.  For
example, some 68000 operating systems call this register @code{%a5}.

Eventually there may be a way of asking the compiler to choose a register
automatically, but first we need to figure out how it should choose and
how to enable you to guide the choice.  No solution is evident.

Defining a global register variable in a certain register reserves that
register entirely for this use, at least within the current compilation.
The register will not be allocated for any other purpose in the functions
in the current compilation.  The register will not be saved and restored by
these functions.  Stores into this register are never deleted even if they
would appear to be dead, but references may be deleted or moved or
simplified.

It is not safe to access the global register variables from signal
handlers, or from more than one thread of control, because the system
library routines may temporarily use the register for other things (unless
you recompile them specially for the task at hand).

@cindex @code{qsort}, and global register variables
It is not safe for one function that uses a global register variable to
call another such function @code{foo} by way of a third function
@code{lose} that was compiled without knowledge of this variable (i.e.@: in a
different source file in which the variable wasn't declared).  This is
because @code{lose} might save the register and put some other value there.
For example, you can't expect a global register variable to be available in
the comparison-function that you pass to @code{qsort}, since @code{qsort}
might have put something else in that register.  (If you are prepared to
recompile @code{qsort} with the same global register variable, you can
solve this problem.)

If you want to recompile @code{qsort} or other source files which do not
actually use your global register variable, so that they will not use that
register for any other purpose, then it suffices to specify the compiler
option @option{-ffixed-@var{reg}}.  You need not actually add a global
register declaration to their source code.

A function which can alter the value of a global register variable cannot
safely be called from a function compiled without this variable, because it
could clobber the value the caller expects to find there on return.
Therefore, the function which is the entry point into the part of the
program that uses the global register variable must explicitly save and
restore the value which belongs to its caller.

@cindex register variable after @code{longjmp}
@cindex global register after @code{longjmp}
@cindex value after @code{longjmp}
@findex longjmp
@findex setjmp
On most machines, @code{longjmp} will restore to each global register
variable the value it had at the time of the @code{setjmp}.  On some
machines, however, @code{longjmp} will not change the value of global
register variables.  To be portable, the function that called @code{setjmp}
should make other arrangements to save the values of the global register
variables, and to restore them in a @code{longjmp}.  This way, the same
thing will happen regardless of what @code{longjmp} does.

All global register variable declarations must precede all function
definitions.  If such a declaration could appear after function
definitions, the declaration would be too late to prevent the register from
being used for other purposes in the preceding functions.

Global register variables may not have initial values, because an
executable file has no means to supply initial contents for a register.

On the SPARC, there are reports that g3 @dots{} g7 are suitable
registers, but certain library functions, such as @code{getwd}, as well
as the subroutines for division and remainder, modify g3 and g4.  g1 and
g2 are local temporaries.

On the 68000, a2 @dots{} a5 should be suitable, as should d2 @dots{} d7.
Of course, it will not do to use more than a few of those.

@node Local Reg Vars
@subsection Specifying Registers for Local Variables
@cindex local variables, specifying registers
@cindex specifying registers for local variables
@cindex registers for local variables

You can define a local register variable with a specified register
like this:

@smallexample
register int *foo asm ("a5");
@end smallexample

@noindent
Here @code{a5} is the name of the register which should be used.  Note
that this is the same syntax used for defining global register
variables, but for a local variable it would appear within a function.

Naturally the register name is cpu-dependent, but this is not a
problem, since specific registers are most often useful with explicit
assembler instructions (@pxref{Extended Asm}).  Both of these things
generally require that you conditionalize your program according to
cpu type.

In addition, operating systems on one type of cpu may differ in how they
name the registers; then you would need additional conditionals.  For
example, some 68000 operating systems call this register @code{%a5}.

Defining such a register variable does not reserve the register; it
remains available for other uses in places where flow control determines
the variable's value is not live.

This option does not guarantee that GCC will generate code that has
this variable in the register you specify at all times.  You may not
code an explicit reference to this register in the @emph{assembler
instruction template} part of an @code{asm} statement and assume it will
always refer to this variable.  However, using the variable as an
@code{asm} @emph{operand} guarantees that the specified register is used
for the operand.

Stores into local register variables may be deleted when they appear to be dead
according to dataflow analysis.  References to local register variables may
be deleted or moved or simplified.

As for global register variables, it's recommended that you choose a
register which is normally saved and restored by function calls on
your machine, so that library routines will not clobber it.  A common
pitfall is to initialize multiple call-clobbered registers with
arbitrary expressions, where a function call or library call for an
arithmetic operator will overwrite a register value from a previous
assignment, for example @code{r0} below:
@smallexample
register int *p1 asm ("r0") = @dots{};
register int *p2 asm ("r1") = @dots{};
@end smallexample
In those cases, a solution is to use a temporary variable for
each arbitrary expression.   @xref{Example of asm with clobbered asm reg}.

@node Alternate Keywords
@section Alternate Keywords
@cindex alternate keywords
@cindex keywords, alternate

@option{-ansi} and the various @option{-std} options disable certain
keywords.  This causes trouble when you want to use GNU C extensions, or
a general-purpose header file that should be usable by all programs,
including ISO C programs.  The keywords @code{asm}, @code{typeof} and
@code{inline} are not available in programs compiled with
@option{-ansi} or @option{-std} (although @code{inline} can be used in a
program compiled with @option{-std=c99}).  The ISO C99 keyword
@code{restrict} is only available when @option{-std=gnu99} (which will
eventually be the default) or @option{-std=c99} (or the equivalent
@option{-std=iso9899:1999}) is used.

The way to solve these problems is to put @samp{__} at the beginning and
end of each problematical keyword.  For example, use @code{__asm__}
instead of @code{asm}, and @code{__inline__} instead of @code{inline}.

Other C compilers won't accept these alternative keywords; if you want to
compile with another compiler, you can define the alternate keywords as
macros to replace them with the customary keywords.  It looks like this:

@smallexample
#ifndef __GNUC__
#define __asm__ asm
#endif
@end smallexample

@findex __extension__
@opindex pedantic
@option{-pedantic} and other options cause warnings for many GNU C extensions.
You can
prevent such warnings within one expression by writing
@code{__extension__} before the expression.  @code{__extension__} has no
effect aside from this.

@node Incomplete Enums
@section Incomplete @code{enum} Types

You can define an @code{enum} tag without specifying its possible values.
This results in an incomplete type, much like what you get if you write
@code{struct foo} without describing the elements.  A later declaration
which does specify the possible values completes the type.

You can't allocate variables or storage using the type while it is
incomplete.  However, you can work with pointers to that type.

This extension may not be very useful, but it makes the handling of
@code{enum} more consistent with the way @code{struct} and @code{union}
are handled.

This extension is not supported by GNU C++.

@node Function Names
@section Function Names as Strings
@cindex @code{__func__} identifier
@cindex @code{__FUNCTION__} identifier
@cindex @code{__PRETTY_FUNCTION__} identifier

GCC provides three magic variables which hold the name of the current
function, as a string.  The first of these is @code{__func__}, which
is part of the C99 standard:

@display
The identifier @code{__func__} is implicitly declared by the translator
as if, immediately following the opening brace of each function
definition, the declaration

@smallexample
static const char __func__[] = "function-name";
@end smallexample

appeared, where function-name is the name of the lexically-enclosing
function.  This name is the unadorned name of the function.
@end display

@code{__FUNCTION__} is another name for @code{__func__}.  Older
versions of GCC recognize only this name.  However, it is not
standardized.  For maximum portability, we recommend you use
@code{__func__}, but provide a fallback definition with the
preprocessor:

@smallexample
#if __STDC_VERSION__ < 199901L
# if __GNUC__ >= 2
#  define __func__ __FUNCTION__
# else
#  define __func__ "<unknown>"
# endif
#endif
@end smallexample

In C, @code{__PRETTY_FUNCTION__} is yet another name for
@code{__func__}.  However, in C++, @code{__PRETTY_FUNCTION__} contains
the type signature of the function as well as its bare name.  For
example, this program:

@smallexample
extern "C" @{
extern int printf (char *, ...);
@}

class a @{
 public:
  void sub (int i)
    @{
      printf ("__FUNCTION__ = %s\n", __FUNCTION__);
      printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__);
    @}
@};

int
main (void)
@{
  a ax;
  ax.sub (0);
  return 0;
@}
@end smallexample

@noindent
gives this output:

@smallexample
__FUNCTION__ = sub
__PRETTY_FUNCTION__ = void a::sub(int)
@end smallexample

These identifiers are not preprocessor macros.  In GCC 3.3 and
earlier, in C only, @code{__FUNCTION__} and @code{__PRETTY_FUNCTION__}
were treated as string literals; they could be used to initialize
@code{char} arrays, and they could be concatenated with other string
literals.  GCC 3.4 and later treat them as variables, like
@code{__func__}.  In C++, @code{__FUNCTION__} and
@code{__PRETTY_FUNCTION__} have always been variables.

@node Return Address
@section Getting the Return or Frame Address of a Function

These functions may be used to get information about the callers of a
function.

@deftypefn {Built-in Function} {void *} __builtin_return_address (unsigned int @var{level})
This function returns the return address of the current function, or of
one of its callers.  The @var{level} argument is number of frames to
scan up the call stack.  A value of @code{0} yields the return address
of the current function, a value of @code{1} yields the return address
of the caller of the current function, and so forth.  When inlining
the expected behavior is that the function will return the address of
the function that will be returned to.  To work around this behavior use
the @code{noinline} function attribute.

The @var{level} argument must be a constant integer.

On some machines it may be impossible to determine the return address of
any function other than the current one; in such cases, or when the top
of the stack has been reached, this function will return @code{0} or a
random value.  In addition, @code{__builtin_frame_address} may be used
to determine if the top of the stack has been reached.

This function should only be used with a nonzero argument for debugging
purposes.
@end deftypefn

@deftypefn {Built-in Function} {void *} __builtin_frame_address (unsigned int @var{level})
This function is similar to @code{__builtin_return_address}, but it
returns the address of the function frame rather than the return address
of the function.  Calling @code{__builtin_frame_address} with a value of
@code{0} yields the frame address of the current function, a value of
@code{1} yields the frame address of the caller of the current function,
and so forth.

The frame is the area on the stack which holds local variables and saved
registers.  The frame address is normally the address of the first word
pushed on to the stack by the function.  However, the exact definition
depends upon the processor and the calling convention.  If the processor
has a dedicated frame pointer register, and the function has a frame,
then @code{__builtin_frame_address} will return the value of the frame
pointer register.

On some machines it may be impossible to determine the frame address of
any function other than the current one; in such cases, or when the top
of the stack has been reached, this function will return @code{0} if
the first frame pointer is properly initialized by the startup code.

This function should only be used with a nonzero argument for debugging
purposes.
@end deftypefn

@node Vector Extensions
@section Using vector instructions through built-in functions

On some targets, the instruction set contains SIMD vector instructions that
operate on multiple values contained in one large register at the same time.
For example, on the i386 the MMX, 3Dnow! and SSE extensions can be used
this way.

The first step in using these extensions is to provide the necessary data
types.  This should be done using an appropriate @code{typedef}:

@smallexample
typedef int v4si __attribute__ ((vector_size (16)));
@end smallexample

The @code{int} type specifies the base type, while the attribute specifies
the vector size for the variable, measured in bytes.  For example, the
declaration above causes the compiler to set the mode for the @code{v4si}
type to be 16 bytes wide and divided into @code{int} sized units.  For
a 32-bit @code{int} this means a vector of 4 units of 4 bytes, and the
corresponding mode of @code{foo} will be @acronym{V4SI}.

The @code{vector_size} attribute is only applicable to integral and
float scalars, although arrays, pointers, and function return values
are allowed in conjunction with this construct.

All the basic integer types can be used as base types, both as signed
and as unsigned: @code{char}, @code{short}, @code{int}, @code{long},
@code{long long}.  In addition, @code{float} and @code{double} can be
used to build floating-point vector types.

Specifying a combination that is not valid for the current architecture
will cause GCC to synthesize the instructions using a narrower mode.
For example, if you specify a variable of type @code{V4SI} and your
architecture does not allow for this specific SIMD type, GCC will
produce code that uses 4 @code{SIs}.

The types defined in this manner can be used with a subset of normal C
operations.  Currently, GCC will allow using the following operators
on these types: @code{+, -, *, /, unary minus, ^, |, &, ~}@.

The operations behave like C++ @code{valarrays}.  Addition is defined as
the addition of the corresponding elements of the operands.  For
example, in the code below, each of the 4 elements in @var{a} will be
added to the corresponding 4 elements in @var{b} and the resulting
vector will be stored in @var{c}.

@smallexample
typedef int v4si __attribute__ ((vector_size (16)));

v4si a, b, c;

c = a + b;
@end smallexample

Subtraction, multiplication, division, and the logical operations
operate in a similar manner.  Likewise, the result of using the unary
minus or complement operators on a vector type is a vector whose
elements are the negative or complemented values of the corresponding
elements in the operand.

You can declare variables and use them in function calls and returns, as
well as in assignments and some casts.  You can specify a vector type as
a return type for a function.  Vector types can also be used as function
arguments.  It is possible to cast from one vector type to another,
provided they are of the same size (in fact, you can also cast vectors
to and from other datatypes of the same size).

You cannot operate between vectors of different lengths or different
signedness without a cast.

A port that supports hardware vector operations, usually provides a set
of built-in functions that can be used to operate on vectors.  For
example, a function to add two vectors and multiply the result by a
third could look like this:

@smallexample
v4si f (v4si a, v4si b, v4si c)
@{
  v4si tmp = __builtin_addv4si (a, b);
  return __builtin_mulv4si (tmp, c);
@}

@end smallexample

@node Offsetof
@section Offsetof
@findex __builtin_offsetof

GCC implements for both C and C++ a syntactic extension to implement
the @code{offsetof} macro.

@smallexample
primary:
	"__builtin_offsetof" "(" @code{typename} "," offsetof_member_designator ")"

offsetof_member_designator:
	  @code{identifier}
	| offsetof_member_designator "." @code{identifier}
	| offsetof_member_designator "[" @code{expr} "]"
@end smallexample

This extension is sufficient such that

@smallexample
#define offsetof(@var{type}, @var{member})  __builtin_offsetof (@var{type}, @var{member})
@end smallexample

is a suitable definition of the @code{offsetof} macro.  In C++, @var{type}
may be dependent.  In either case, @var{member} may consist of a single
identifier, or a sequence of member accesses and array references.

@node Atomic Builtins
@section Built-in functions for atomic memory access

The following builtins are intended to be compatible with those described
in the @cite{Intel Itanium Processor-specific Application Binary Interface},
section 7.4.  As such, they depart from the normal GCC practice of using
the ``__builtin_'' prefix, and further that they are overloaded such that
they work on multiple types.

The definition given in the Intel documentation allows only for the use of
the types @code{int}, @code{long}, @code{long long} as well as their unsigned
counterparts.  GCC will allow any integral scalar or pointer type that is
1, 2, 4 or 8 bytes in length.

Not all operations are supported by all target processors.  If a particular
operation cannot be implemented on the target processor, a warning will be
generated and a call an external function will be generated.  The external
function will carry the same name as the builtin, with an additional suffix
@samp{_@var{n}} where @var{n} is the size of the data type.

@c ??? Should we have a mechanism to suppress this warning?  This is almost
@c useful for implementing the operation under the control of an external
@c mutex.

In most cases, these builtins are considered a @dfn{full barrier}.  That is,
no memory operand will be moved across the operation, either forward or
backward.  Further, instructions will be issued as necessary to prevent the
processor from speculating loads across the operation and from queuing stores
after the operation.

All of the routines are are described in the Intel documentation to take
``an optional list of variables protected by the memory barrier''.  It's
not clear what is meant by that; it could mean that @emph{only} the
following variables are protected, or it could mean that these variables
should in addition be protected.  At present GCC ignores this list and
protects all variables which are globally accessible.  If in the future
we make some use of this list, an empty list will continue to mean all
globally accessible variables.

@table @code
@item @var{type} __sync_fetch_and_add (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_fetch_and_sub (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_fetch_and_or (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_fetch_and_and (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_fetch_and_xor (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_fetch_and_nand (@var{type} *ptr, @var{type} value, ...)
@findex __sync_fetch_and_add
@findex __sync_fetch_and_sub
@findex __sync_fetch_and_or
@findex __sync_fetch_and_and
@findex __sync_fetch_and_xor
@findex __sync_fetch_and_nand
These builtins perform the operation suggested by the name, and
returns the value that had previously been in memory.  That is,

@smallexample
@{ tmp = *ptr; *ptr @var{op}= value; return tmp; @}
@{ tmp = *ptr; *ptr = ~tmp & value; return tmp; @}   // nand
@end smallexample

@item @var{type} __sync_add_and_fetch (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_sub_and_fetch (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_or_and_fetch (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_and_and_fetch (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_xor_and_fetch (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_nand_and_fetch (@var{type} *ptr, @var{type} value, ...)
@findex __sync_add_and_fetch
@findex __sync_sub_and_fetch
@findex __sync_or_and_fetch
@findex __sync_and_and_fetch
@findex __sync_xor_and_fetch
@findex __sync_nand_and_fetch
These builtins perform the operation suggested by the name, and
return the new value.  That is,

@smallexample
@{ *ptr @var{op}= value; return *ptr; @}
@{ *ptr = ~*ptr & value; return *ptr; @}   // nand
@end smallexample

@item bool __sync_bool_compare_and_swap (@var{type} *ptr, @var{type} oldval @var{type} newval, ...)
@itemx @var{type} __sync_val_compare_and_swap (@var{type} *ptr, @var{type} oldval @var{type} newval, ...)
@findex __sync_bool_compare_and_swap
@findex __sync_val_compare_and_swap
These builtins perform an atomic compare and swap.  That is, if the current
value of @code{*@var{ptr}} is @var{oldval}, then write @var{newval} into
@code{*@var{ptr}}.

The ``bool'' version returns true if the comparison is successful and
@var{newval} was written.  The ``val'' version returns the contents
of @code{*@var{ptr}} before the operation.

@item __sync_synchronize (...)
@findex __sync_synchronize
This builtin issues a full memory barrier.

@item @var{type} __sync_lock_test_and_set (@var{type} *ptr, @var{type} value, ...)
@findex __sync_lock_test_and_set
This builtin, as described by Intel, is not a traditional test-and-set
operation, but rather an atomic exchange operation.  It writes @var{value}
into @code{*@var{ptr}}, and returns the previous contents of
@code{*@var{ptr}}.

Many targets have only minimal support for such locks, and do not support
a full exchange operation.  In this case, a target may support reduced
functionality here by which the @emph{only} valid value to store is the
immediate constant 1.  The exact value actually stored in @code{*@var{ptr}}
is implementation defined.

This builtin is not a full barrier, but rather an @dfn{acquire barrier}.
This means that references after the builtin cannot move to (or be
speculated to) before the builtin, but previous memory stores may not
be globally visible yet, and previous memory loads may not yet be
satisfied.

@item void __sync_lock_release (@var{type} *ptr, ...)
@findex __sync_lock_release
This builtin releases the lock acquired by @code{__sync_lock_test_and_set}.
Normally this means writing the constant 0 to @code{*@var{ptr}}.

This builtin is not a full barrier, but rather a @dfn{release barrier}.
This means that all previous memory stores are globally visible, and all
previous memory loads have been satisfied, but following memory reads
are not prevented from being speculated to before the barrier.
@end table

@node Object Size Checking
@section Object Size Checking Builtins
@findex __builtin_object_size
@findex __builtin___memcpy_chk
@findex __builtin___mempcpy_chk
@findex __builtin___memmove_chk
@findex __builtin___memset_chk
@findex __builtin___strcpy_chk
@findex __builtin___stpcpy_chk
@findex __builtin___strncpy_chk
@findex __builtin___strcat_chk
@findex __builtin___strncat_chk
@findex __builtin___sprintf_chk
@findex __builtin___snprintf_chk
@findex __builtin___vsprintf_chk
@findex __builtin___vsnprintf_chk
@findex __builtin___printf_chk
@findex __builtin___vprintf_chk
@findex __builtin___fprintf_chk
@findex __builtin___vfprintf_chk

GCC implements a limited buffer overflow protection mechanism
that can prevent some buffer overflow attacks.

@deftypefn {Built-in Function} {size_t} __builtin_object_size (void * @var{ptr}, int @var{type})
is a built-in construct that returns a constant number of bytes from
@var{ptr} to the end of the object @var{ptr} pointer points to
(if known at compile time).  @code{__builtin_object_size} never evaluates
its arguments for side-effects.  If there are any side-effects in them, it
returns @code{(size_t) -1} for @var{type} 0 or 1 and @code{(size_t) 0}
for @var{type} 2 or 3.  If there are multiple objects @var{ptr} can
point to and all of them are known at compile time, the returned number
is the maximum of remaining byte counts in those objects if @var{type} & 2 is
0 and minimum if nonzero.  If it is not possible to determine which objects
@var{ptr} points to at compile time, @code{__builtin_object_size} should
return @code{(size_t) -1} for @var{type} 0 or 1 and @code{(size_t) 0}
for @var{type} 2 or 3.

@var{type} is an integer constant from 0 to 3.  If the least significant
bit is clear, objects are whole variables, if it is set, a closest
surrounding subobject is considered the object a pointer points to.
The second bit determines if maximum or minimum of remaining bytes
is computed.

@smallexample
struct V @{ char buf1[10]; int b; char buf2[10]; @} var;
char *p = &var.buf1[1], *q = &var.b;

/* Here the object p points to is var.  */
assert (__builtin_object_size (p, 0) == sizeof (var) - 1);
/* The subobject p points to is var.buf1.  */
assert (__builtin_object_size (p, 1) == sizeof (var.buf1) - 1);
/* The object q points to is var.  */
assert (__builtin_object_size (q, 0)
	== (char *) (&var + 1) - (char *) &var.b);
/* The subobject q points to is var.b.  */
assert (__builtin_object_size (q, 1) == sizeof (var.b));
@end smallexample
@end deftypefn

There are built-in functions added for many common string operation
functions, e.g. for @code{memcpy} @code{__builtin___memcpy_chk}
built-in is provided.  This built-in has an additional last argument,
which is the number of bytes remaining in object the @var{dest}
argument points to or @code{(size_t) -1} if the size is not known.

The built-in functions are optimized into the normal string functions
like @code{memcpy} if the last argument is @code{(size_t) -1} or if
it is known at compile time that the destination object will not
be overflown.  If the compiler can determine at compile time the
object will be always overflown, it issues a warning.

The intended use can be e.g.

@smallexample
#undef memcpy
#define bos0(dest) __builtin_object_size (dest, 0)
#define memcpy(dest, src, n) \
  __builtin___memcpy_chk (dest, src, n, bos0 (dest))

char *volatile p;
char buf[10];
/* It is unknown what object p points to, so this is optimized
   into plain memcpy - no checking is possible.  */
memcpy (p, "abcde", n);
/* Destination is known and length too.  It is known at compile
   time there will be no overflow.  */
memcpy (&buf[5], "abcde", 5);
/* Destination is known, but the length is not known at compile time.
   This will result in __memcpy_chk call that can check for overflow
   at runtime.  */
memcpy (&buf[5], "abcde", n);
/* Destination is known and it is known at compile time there will
   be overflow.  There will be a warning and __memcpy_chk call that
   will abort the program at runtime.  */
memcpy (&buf[6], "abcde", 5);
@end smallexample

Such built-in functions are provided for @code{memcpy}, @code{mempcpy},
@code{memmove}, @code{memset}, @code{strcpy}, @code{stpcpy}, @code{strncpy},
@code{strcat} and @code{strncat}.

There are also checking built-in functions for formatted output functions.
@smallexample
int __builtin___sprintf_chk (char *s, int flag, size_t os, const char *fmt, ...);
int __builtin___snprintf_chk (char *s, size_t maxlen, int flag, size_t os,
			      const char *fmt, ...);
int __builtin___vsprintf_chk (char *s, int flag, size_t os, const char *fmt,
			      va_list ap);
int __builtin___vsnprintf_chk (char *s, size_t maxlen, int flag, size_t os,
			       const char *fmt, va_list ap);
@end smallexample

The added @var{flag} argument is passed unchanged to @code{__sprintf_chk}
etc. functions and can contain implementation specific flags on what
additional security measures the checking function might take, such as
handling @code{%n} differently.

The @var{os} argument is the object size @var{s} points to, like in the
other built-in functions.  There is a small difference in the behavior
though, if @var{os} is @code{(size_t) -1}, the built-in functions are
optimized into the non-checking functions only if @var{flag} is 0, otherwise
the checking function is called with @var{os} argument set to
@code{(size_t) -1}.

In addition to this, there are checking built-in functions
@code{__builtin___printf_chk}, @code{__builtin___vprintf_chk},
@code{__builtin___fprintf_chk} and @code{__builtin___vfprintf_chk}.
These have just one additional argument, @var{flag}, right before
format string @var{fmt}.  If the compiler is able to optimize them to
@code{fputc} etc. functions, it will, otherwise the checking function
should be called and the @var{flag} argument passed to it.

@node Other Builtins
@section Other built-in functions provided by GCC
@cindex built-in functions
@findex __builtin_isgreater
@findex __builtin_isgreaterequal
@findex __builtin_isless
@findex __builtin_islessequal
@findex __builtin_islessgreater
@findex __builtin_isunordered
@findex __builtin_powi
@findex __builtin_powif
@findex __builtin_powil
@findex _Exit
@findex _exit
@findex abort
@findex abs
@findex acos
@findex acosf
@findex acosh
@findex acoshf
@findex acoshl
@findex acosl
@findex alloca
@findex asin
@findex asinf
@findex asinh
@findex asinhf
@findex asinhl
@findex asinl
@findex atan
@findex atan2
@findex atan2f
@findex atan2l
@findex atanf
@findex atanh
@findex atanhf
@findex atanhl
@findex atanl
@findex bcmp
@findex bzero
@findex cabs
@findex cabsf
@findex cabsl
@findex cacos
@findex cacosf
@findex cacosh
@findex cacoshf
@findex cacoshl
@findex cacosl
@findex calloc
@findex carg
@findex cargf
@findex cargl
@findex casin
@findex casinf
@findex casinh
@findex casinhf
@findex casinhl
@findex casinl
@findex catan
@findex catanf
@findex catanh
@findex catanhf
@findex catanhl
@findex catanl
@findex cbrt
@findex cbrtf
@findex cbrtl
@findex ccos
@findex ccosf
@findex ccosh
@findex ccoshf
@findex ccoshl
@findex ccosl
@findex ceil
@findex ceilf
@findex ceill
@findex cexp
@findex cexpf
@findex cexpl
@findex cimag
@findex cimagf
@findex cimagl
@findex clog
@findex clogf
@findex clogl
@findex conj
@findex conjf
@findex conjl
@findex copysign
@findex copysignf
@findex copysignl
@findex cos
@findex cosf
@findex cosh
@findex coshf
@findex coshl
@findex cosl
@findex cpow
@findex cpowf
@findex cpowl
@findex cproj
@findex cprojf
@findex cprojl
@findex creal
@findex crealf
@findex creall
@findex csin
@findex csinf
@findex csinh
@findex csinhf
@findex csinhl
@findex csinl
@findex csqrt
@findex csqrtf
@findex csqrtl
@findex ctan
@findex ctanf
@findex ctanh
@findex ctanhf
@findex ctanhl
@findex ctanl
@findex dcgettext
@findex dgettext
@findex drem
@findex dremf
@findex dreml
@findex erf
@findex erfc
@findex erfcf
@findex erfcl
@findex erff
@findex erfl
@findex exit
@findex exp
@findex exp10
@findex exp10f
@findex exp10l
@findex exp2
@findex exp2f
@findex exp2l
@findex expf
@findex expl
@findex expm1
@findex expm1f
@findex expm1l
@findex fabs
@findex fabsf
@findex fabsl
@findex fdim
@findex fdimf
@findex fdiml
@findex ffs
@findex floor
@findex floorf
@findex floorl
@findex fma
@findex fmaf
@findex fmal
@findex fmax
@findex fmaxf
@findex fmaxl
@findex fmin
@findex fminf
@findex fminl
@findex fmod
@findex fmodf
@findex fmodl
@findex fprintf
@findex fprintf_unlocked
@findex fputs
@findex fputs_unlocked
@findex frexp
@findex frexpf
@findex frexpl
@findex fscanf
@findex gamma
@findex gammaf
@findex gammal
@findex gettext
@findex hypot
@findex hypotf
@findex hypotl
@findex ilogb
@findex ilogbf
@findex ilogbl
@findex imaxabs
@findex index
@findex isalnum
@findex isalpha
@findex isascii
@findex isblank
@findex iscntrl
@findex isdigit
@findex isgraph
@findex islower
@findex isprint
@findex ispunct
@findex isspace
@findex isupper
@findex iswalnum
@findex iswalpha
@findex iswblank
@findex iswcntrl
@findex iswdigit
@findex iswgraph
@findex iswlower
@findex iswprint
@findex iswpunct
@findex iswspace
@findex iswupper
@findex iswxdigit
@findex isxdigit
@findex j0
@findex j0f
@findex j0l
@findex j1
@findex j1f
@findex j1l
@findex jn
@findex jnf
@findex jnl
@findex labs
@findex ldexp
@findex ldexpf
@findex ldexpl
@findex lgamma
@findex lgammaf
@findex lgammal
@findex llabs
@findex llrint
@findex llrintf
@findex llrintl
@findex llround
@findex llroundf
@findex llroundl
@findex log
@findex log10
@findex log10f
@findex log10l
@findex log1p
@findex log1pf
@findex log1pl
@findex log2
@findex log2f
@findex log2l
@findex logb
@findex logbf
@findex logbl
@findex logf
@findex logl
@findex lrint
@findex lrintf
@findex lrintl
@findex lround
@findex lroundf
@findex lroundl
@findex malloc
@findex memcmp
@findex memcpy
@findex mempcpy
@findex memset
@findex modf
@findex modff
@findex modfl
@findex nearbyint
@findex nearbyintf
@findex nearbyintl
@findex nextafter
@findex nextafterf
@findex nextafterl
@findex nexttoward
@findex nexttowardf
@findex nexttowardl
@findex pow
@findex pow10
@findex pow10f
@findex pow10l
@findex powf
@findex powl
@findex printf
@findex printf_unlocked
@findex putchar
@findex puts
@findex remainder
@findex remainderf
@findex remainderl
@findex remquo
@findex remquof
@findex remquol
@findex rindex
@findex rint
@findex rintf
@findex rintl
@findex round
@findex roundf
@findex roundl
@findex scalb
@findex scalbf
@findex scalbl
@findex scalbln
@findex scalblnf
@findex scalblnf
@findex scalbn
@findex scalbnf
@findex scanfnl
@findex signbit
@findex signbitf
@findex signbitl
@findex significand
@findex significandf
@findex significandl
@findex sin
@findex sincos
@findex sincosf
@findex sincosl
@findex sinf
@findex sinh
@findex sinhf
@findex sinhl
@findex sinl
@findex snprintf
@findex sprintf
@findex sqrt
@findex sqrtf
@findex sqrtl
@findex sscanf
@findex stpcpy
@findex stpncpy
@findex strcasecmp
@findex strcat
@findex strchr
@findex strcmp
@findex strcpy
@findex strcspn
@findex strdup
@findex strfmon
@findex strftime
@findex strlen
@findex strncasecmp
@findex strncat
@findex strncmp
@findex strncpy
@findex strndup
@findex strpbrk
@findex strrchr
@findex strspn
@findex strstr
@findex tan
@findex tanf
@findex tanh
@findex tanhf
@findex tanhl
@findex tanl
@findex tgamma
@findex tgammaf
@findex tgammal
@findex toascii
@findex tolower
@findex toupper
@findex towlower
@findex towupper
@findex trunc
@findex truncf
@findex truncl
@findex vfprintf
@findex vfscanf
@findex vprintf
@findex vscanf
@findex vsnprintf
@findex vsprintf
@findex vsscanf
@findex y0
@findex y0f
@findex y0l
@findex y1
@findex y1f
@findex y1l
@findex yn
@findex ynf
@findex ynl

GCC provides a large number of built-in functions other than the ones
mentioned above.  Some of these are for internal use in the processing
of exceptions or variable-length argument lists and will not be
documented here because they may change from time to time; we do not
recommend general use of these functions.

The remaining functions are provided for optimization purposes.

@opindex fno-builtin
GCC includes built-in versions of many of the functions in the standard
C library.  The versions prefixed with @code{__builtin_} will always be
treated as having the same meaning as the C library function even if you
specify the @option{-fno-builtin} option.  (@pxref{C Dialect Options})
Many of these functions are only optimized in certain cases; if they are
not optimized in a particular case, a call to the library function will
be emitted.

@opindex ansi
@opindex std
Outside strict ISO C mode (@option{-ansi}, @option{-std=c89} or
@option{-std=c99}), the functions
@code{_exit}, @code{alloca}, @code{bcmp}, @code{bzero},
@code{dcgettext}, @code{dgettext}, @code{dremf}, @code{dreml},
@code{drem}, @code{exp10f}, @code{exp10l}, @code{exp10}, @code{ffsll},
@code{ffsl}, @code{ffs}, @code{fprintf_unlocked}, @code{fputs_unlocked},
@code{gammaf}, @code{gammal}, @code{gamma}, @code{gettext},
@code{index}, @code{isascii}, @code{j0f}, @code{j0l}, @code{j0},
@code{j1f}, @code{j1l}, @code{j1}, @code{jnf}, @code{jnl}, @code{jn},
@code{mempcpy}, @code{pow10f}, @code{pow10l}, @code{pow10},
@code{printf_unlocked}, @code{rindex}, @code{scalbf}, @code{scalbl},
@code{scalb}, @code{signbit}, @code{signbitf}, @code{signbitl},
@code{significandf}, @code{significandl}, @code{significand},
@code{sincosf}, @code{sincosl}, @code{sincos}, @code{stpcpy},
@code{stpncpy}, @code{strcasecmp}, @code{strdup}, @code{strfmon},
@code{strncasecmp}, @code{strndup}, @code{toascii}, @code{y0f},
@code{y0l}, @code{y0}, @code{y1f}, @code{y1l}, @code{y1}, @code{ynf},
@code{ynl} and @code{yn}
may be handled as built-in functions.
All these functions have corresponding versions
prefixed with @code{__builtin_}, which may be used even in strict C89
mode.

The ISO C99 functions
@code{_Exit}, @code{acoshf}, @code{acoshl}, @code{acosh}, @code{asinhf},
@code{asinhl}, @code{asinh}, @code{atanhf}, @code{atanhl}, @code{atanh},
@code{cabsf}, @code{cabsl}, @code{cabs}, @code{cacosf}, @code{cacoshf},
@code{cacoshl}, @code{cacosh}, @code{cacosl}, @code{cacos},
@code{cargf}, @code{cargl}, @code{carg}, @code{casinf}, @code{casinhf},
@code{casinhl}, @code{casinh}, @code{casinl}, @code{casin},
@code{catanf}, @code{catanhf}, @code{catanhl}, @code{catanh},
@code{catanl}, @code{catan}, @code{cbrtf}, @code{cbrtl}, @code{cbrt},
@code{ccosf}, @code{ccoshf}, @code{ccoshl}, @code{ccosh}, @code{ccosl},
@code{ccos}, @code{cexpf}, @code{cexpl}, @code{cexp}, @code{cimagf},
@code{cimagl}, @code{cimag}, @code{clogf}, @code{clogl}, @code{clog},
@code{conjf}, @code{conjl}, @code{conj}, @code{copysignf}, @code{copysignl},
@code{copysign}, @code{cpowf}, @code{cpowl}, @code{cpow}, @code{cprojf},
@code{cprojl}, @code{cproj}, @code{crealf}, @code{creall}, @code{creal},
@code{csinf}, @code{csinhf}, @code{csinhl}, @code{csinh}, @code{csinl},
@code{csin}, @code{csqrtf}, @code{csqrtl}, @code{csqrt}, @code{ctanf},
@code{ctanhf}, @code{ctanhl}, @code{ctanh}, @code{ctanl}, @code{ctan},
@code{erfcf}, @code{erfcl}, @code{erfc}, @code{erff}, @code{erfl},
@code{erf}, @code{exp2f}, @code{exp2l}, @code{exp2}, @code{expm1f},
@code{expm1l}, @code{expm1}, @code{fdimf}, @code{fdiml}, @code{fdim},
@code{fmaf}, @code{fmal}, @code{fmaxf}, @code{fmaxl}, @code{fmax},
@code{fma}, @code{fminf}, @code{fminl}, @code{fmin}, @code{hypotf},
@code{hypotl}, @code{hypot}, @code{ilogbf}, @code{ilogbl}, @code{ilogb},
@code{imaxabs}, @code{isblank}, @code{iswblank}, @code{lgammaf},
@code{lgammal}, @code{lgamma}, @code{llabs}, @code{llrintf}, @code{llrintl},
@code{llrint}, @code{llroundf}, @code{llroundl}, @code{llround},
@code{log1pf}, @code{log1pl}, @code{log1p}, @code{log2f}, @code{log2l},
@code{log2}, @code{logbf}, @code{logbl}, @code{logb}, @code{lrintf},
@code{lrintl}, @code{lrint}, @code{lroundf}, @code{lroundl},
@code{lround}, @code{nearbyintf}, @code{nearbyintl}, @code{nearbyint},
@code{nextafterf}, @code{nextafterl}, @code{nextafter},
@code{nexttowardf}, @code{nexttowardl}, @code{nexttoward},
@code{remainderf}, @code{remainderl}, @code{remainder}, @code{remquof},
@code{remquol}, @code{remquo}, @code{rintf}, @code{rintl}, @code{rint},
@code{roundf}, @code{roundl}, @code{round}, @code{scalblnf},
@code{scalblnl}, @code{scalbln}, @code{scalbnf}, @code{scalbnl},
@code{scalbn}, @code{snprintf}, @code{tgammaf}, @code{tgammal},
@code{tgamma}, @code{truncf}, @code{truncl}, @code{trunc},
@code{vfscanf}, @code{vscanf}, @code{vsnprintf} and @code{vsscanf}
are handled as built-in functions
except in strict ISO C90 mode (@option{-ansi} or @option{-std=c89}).

There are also built-in versions of the ISO C99 functions
@code{acosf}, @code{acosl}, @code{asinf}, @code{asinl}, @code{atan2f},
@code{atan2l}, @code{atanf}, @code{atanl}, @code{ceilf}, @code{ceill},
@code{cosf}, @code{coshf}, @code{coshl}, @code{cosl}, @code{expf},
@code{expl}, @code{fabsf}, @code{fabsl}, @code{floorf}, @code{floorl},
@code{fmodf}, @code{fmodl}, @code{frexpf}, @code{frexpl}, @code{ldexpf},
@code{ldexpl}, @code{log10f}, @code{log10l}, @code{logf}, @code{logl},
@code{modfl}, @code{modf}, @code{powf}, @code{powl}, @code{sinf},
@code{sinhf}, @code{sinhl}, @code{sinl}, @code{sqrtf}, @code{sqrtl},
@code{tanf}, @code{tanhf}, @code{tanhl} and @code{tanl}
that are recognized in any mode since ISO C90 reserves these names for
the purpose to which ISO C99 puts them.  All these functions have
corresponding versions prefixed with @code{__builtin_}.

The ISO C94 functions
@code{iswalnum}, @code{iswalpha}, @code{iswcntrl}, @code{iswdigit},
@code{iswgraph}, @code{iswlower}, @code{iswprint}, @code{iswpunct},
@code{iswspace}, @code{iswupper}, @code{iswxdigit}, @code{towlower} and
@code{towupper}
are handled as built-in functions
except in strict ISO C90 mode (@option{-ansi} or @option{-std=c89}).

The ISO C90 functions
@code{abort}, @code{abs}, @code{acos}, @code{asin}, @code{atan2},
@code{atan}, @code{calloc}, @code{ceil}, @code{cosh}, @code{cos},
@code{exit}, @code{exp}, @code{fabs}, @code{floor}, @code{fmod},
@code{fprintf}, @code{fputs}, @code{frexp}, @code{fscanf},
@code{isalnum}, @code{isalpha}, @code{iscntrl}, @code{isdigit},
@code{isgraph}, @code{islower}, @code{isprint}, @code{ispunct},
@code{isspace}, @code{isupper}, @code{isxdigit}, @code{tolower},
@code{toupper}, @code{labs}, @code{ldexp}, @code{log10}, @code{log},
@code{malloc}, @code{memcmp}, @code{memcpy}, @code{memset}, @code{modf},
@code{pow}, @code{printf}, @code{putchar}, @code{puts}, @code{scanf},
@code{sinh}, @code{sin}, @code{snprintf}, @code{sprintf}, @code{sqrt},
@code{sscanf}, @code{strcat}, @code{strchr}, @code{strcmp},
@code{strcpy}, @code{strcspn}, @code{strlen}, @code{strncat},
@code{strncmp}, @code{strncpy}, @code{strpbrk}, @code{strrchr},
@code{strspn}, @code{strstr}, @code{tanh}, @code{tan}, @code{vfprintf},
@code{vprintf} and @code{vsprintf}
are all recognized as built-in functions unless
@option{-fno-builtin} is specified (or @option{-fno-builtin-@var{function}}
is specified for an individual function).  All of these functions have
corresponding versions prefixed with @code{__builtin_}.

GCC provides built-in versions of the ISO C99 floating point comparison
macros that avoid raising exceptions for unordered operands.  They have
the same names as the standard macros ( @code{isgreater},
@code{isgreaterequal}, @code{isless}, @code{islessequal},
@code{islessgreater}, and @code{isunordered}) , with @code{__builtin_}
prefixed.  We intend for a library implementor to be able to simply
@code{#define} each standard macro to its built-in equivalent.

@deftypefn {Built-in Function} int __builtin_types_compatible_p (@var{type1}, @var{type2})

You can use the built-in function @code{__builtin_types_compatible_p} to
determine whether two types are the same.

This built-in function returns 1 if the unqualified versions of the
types @var{type1} and @var{type2} (which are types, not expressions) are
compatible, 0 otherwise.  The result of this built-in function can be
used in integer constant expressions.

This built-in function ignores top level qualifiers (e.g., @code{const},
@code{volatile}).  For example, @code{int} is equivalent to @code{const
int}.

The type @code{int[]} and @code{int[5]} are compatible.  On the other
hand, @code{int} and @code{char *} are not compatible, even if the size
of their types, on the particular architecture are the same.  Also, the
amount of pointer indirection is taken into account when determining
similarity.  Consequently, @code{short *} is not similar to
@code{short **}.  Furthermore, two types that are typedefed are
considered compatible if their underlying types are compatible.

An @code{enum} type is not considered to be compatible with another
@code{enum} type even if both are compatible with the same integer
type; this is what the C standard specifies.
For example, @code{enum @{foo, bar@}} is not similar to
@code{enum @{hot, dog@}}.

You would typically use this function in code whose execution varies
depending on the arguments' types.  For example:

@smallexample
#define foo(x)                                                  \
  (@{                                                           \
    typeof (x) tmp = (x);                                       \
    if (__builtin_types_compatible_p (typeof (x), long double)) \
      tmp = foo_long_double (tmp);                              \
    else if (__builtin_types_compatible_p (typeof (x), double)) \
      tmp = foo_double (tmp);                                   \
    else if (__builtin_types_compatible_p (typeof (x), float))  \
      tmp = foo_float (tmp);                                    \
    else                                                        \
      abort ();                                                 \
    tmp;                                                        \
  @})
@end smallexample

@emph{Note:} This construct is only available for C@.

@end deftypefn

@deftypefn {Built-in Function} @var{type} __builtin_choose_expr (@var{const_exp}, @var{exp1}, @var{exp2})

You can use the built-in function @code{__builtin_choose_expr} to
evaluate code depending on the value of a constant expression.  This
built-in function returns @var{exp1} if @var{const_exp}, which is a
constant expression that must be able to be determined at compile time,
is nonzero.  Otherwise it returns 0.

This built-in function is analogous to the @samp{? :} operator in C,
except that the expression returned has its type unaltered by promotion
rules.  Also, the built-in function does not evaluate the expression
that was not chosen.  For example, if @var{const_exp} evaluates to true,
@var{exp2} is not evaluated even if it has side-effects.

This built-in function can return an lvalue if the chosen argument is an
lvalue.

If @var{exp1} is returned, the return type is the same as @var{exp1}'s
type.  Similarly, if @var{exp2} is returned, its return type is the same
as @var{exp2}.

Example:

@smallexample
#define foo(x)                                                    \
  __builtin_choose_expr (                                         \
    __builtin_types_compatible_p (typeof (x), double),            \
    foo_double (x),                                               \
    __builtin_choose_expr (                                       \
      __builtin_types_compatible_p (typeof (x), float),           \
      foo_float (x),                                              \
      /* @r{The void expression results in a compile-time error}  \
         @r{when assigning the result to something.}  */          \
      (void)0))
@end smallexample

@emph{Note:} This construct is only available for C@.  Furthermore, the
unused expression (@var{exp1} or @var{exp2} depending on the value of
@var{const_exp}) may still generate syntax errors.  This may change in
future revisions.

@end deftypefn

@deftypefn {Built-in Function} int __builtin_constant_p (@var{exp})
You can use the built-in function @code{__builtin_constant_p} to
determine if a value is known to be constant at compile-time and hence
that GCC can perform constant-folding on expressions involving that
value.  The argument of the function is the value to test.  The function
returns the integer 1 if the argument is known to be a compile-time
constant and 0 if it is not known to be a compile-time constant.  A
return of 0 does not indicate that the value is @emph{not} a constant,
but merely that GCC cannot prove it is a constant with the specified
value of the @option{-O} option.

You would typically use this function in an embedded application where
memory was a critical resource.  If you have some complex calculation,
you may want it to be folded if it involves constants, but need to call
a function if it does not.  For example:

@smallexample
#define Scale_Value(X)      \
  (__builtin_constant_p (X) \
  ? ((X) * SCALE + OFFSET) : Scale (X))
@end smallexample

You may use this built-in function in either a macro or an inline
function.  However, if you use it in an inlined function and pass an
argument of the function as the argument to the built-in, GCC will
never return 1 when you call the inline function with a string constant
or compound literal (@pxref{Compound Literals}) and will not return 1
when you pass a constant numeric value to the inline function unless you
specify the @option{-O} option.

You may also use @code{__builtin_constant_p} in initializers for static
data.  For instance, you can write

@smallexample
static const int table[] = @{
   __builtin_constant_p (EXPRESSION) ? (EXPRESSION) : -1,
   /* @r{@dots{}} */
@};
@end smallexample

@noindent
This is an acceptable initializer even if @var{EXPRESSION} is not a
constant expression.  GCC must be more conservative about evaluating the
built-in in this case, because it has no opportunity to perform
optimization.

Previous versions of GCC did not accept this built-in in data
initializers.  The earliest version where it is completely safe is
3.0.1.
@end deftypefn

@deftypefn {Built-in Function} long __builtin_expect (long @var{exp}, long @var{c})
@opindex fprofile-arcs
You may use @code{__builtin_expect} to provide the compiler with
branch prediction information.  In general, you should prefer to
use actual profile feedback for this (@option{-fprofile-arcs}), as
programmers are notoriously bad at predicting how their programs
actually perform.  However, there are applications in which this
data is hard to collect.

The return value is the value of @var{exp}, which should be an
integral expression.  The value of @var{c} must be a compile-time
constant.  The semantics of the built-in are that it is expected
that @var{exp} == @var{c}.  For example:

@smallexample
if (__builtin_expect (x, 0))
  foo ();
@end smallexample

@noindent
would indicate that we do not expect to call @code{foo}, since
we expect @code{x} to be zero.  Since you are limited to integral
expressions for @var{exp}, you should use constructions such as

@smallexample
if (__builtin_expect (ptr != NULL, 1))
  error ();
@end smallexample

@noindent
when testing pointer or floating-point values.
@end deftypefn

@deftypefn {Built-in Function} void __builtin_prefetch (const void *@var{addr}, ...)
This function is used to minimize cache-miss latency by moving data into
a cache before it is accessed.
You can insert calls to @code{__builtin_prefetch} into code for which
you know addresses of data in memory that is likely to be accessed soon.
If the target supports them, data prefetch instructions will be generated.
If the prefetch is done early enough before the access then the data will
be in the cache by the time it is accessed.

The value of @var{addr} is the address of the memory to prefetch.
There are two optional arguments, @var{rw} and @var{locality}.
The value of @var{rw} is a compile-time constant one or zero; one
means that the prefetch is preparing for a write to the memory address
and zero, the default, means that the prefetch is preparing for a read.
The value @var{locality} must be a compile-time constant integer between
zero and three.  A value of zero means that the data has no temporal
locality, so it need not be left in the cache after the access.  A value
of three means that the data has a high degree of temporal locality and
should be left in all levels of cache possible.  Values of one and two
mean, respectively, a low or moderate degree of temporal locality.  The
default is three.

@smallexample
for (i = 0; i < n; i++)
  @{
    a[i] = a[i] + b[i];
    __builtin_prefetch (&a[i+j], 1, 1);
    __builtin_prefetch (&b[i+j], 0, 1);
    /* @r{@dots{}} */
  @}
@end smallexample

Data prefetch does not generate faults if @var{addr} is invalid, but
the address expression itself must be valid.  For example, a prefetch
of @code{p->next} will not fault if @code{p->next} is not a valid
address, but evaluation will fault if @code{p} is not a valid address.

If the target does not support data prefetch, the address expression
is evaluated if it includes side effects but no other code is generated
and GCC does not issue a warning.
@end deftypefn

@deftypefn {Built-in Function} double __builtin_huge_val (void)
Returns a positive infinity, if supported by the floating-point format,
else @code{DBL_MAX}.  This function is suitable for implementing the
ISO C macro @code{HUGE_VAL}.
@end deftypefn

@deftypefn {Built-in Function} float __builtin_huge_valf (void)
Similar to @code{__builtin_huge_val}, except the return type is @code{float}.
@end deftypefn

@deftypefn {Built-in Function} {long double} __builtin_huge_vall (void)
Similar to @code{__builtin_huge_val}, except the return
type is @code{long double}.
@end deftypefn

@deftypefn {Built-in Function} double __builtin_inf (void)
Similar to @code{__builtin_huge_val}, except a warning is generated
if the target floating-point format does not support infinities.
@end deftypefn

@deftypefn {Built-in Function} _Decimal32 __builtin_infd32 (void)
Similar to @code{__builtin_inf}, except the return type is @code{_Decimal32}.
@end deftypefn

@deftypefn {Built-in Function} _Decimal64 __builtin_infd64 (void)
Similar to @code{__builtin_inf}, except the return type is @code{_Decimal64}.
@end deftypefn

@deftypefn {Built-in Function} _Decimal128 __builtin_infd128 (void)
Similar to @code{__builtin_inf}, except the return type is @code{_Decimal128}.
@end deftypefn

@deftypefn {Built-in Function} float __builtin_inff (void)
Similar to @code{__builtin_inf}, except the return type is @code{float}.
This function is suitable for implementing the ISO C99 macro @code{INFINITY}.
@end deftypefn

@deftypefn {Built-in Function} {long double} __builtin_infl (void)
Similar to @code{__builtin_inf}, except the return
type is @code{long double}.
@end deftypefn

@deftypefn {Built-in Function} double __builtin_nan (const char *str)
This is an implementation of the ISO C99 function @code{nan}.

Since ISO C99 defines this function in terms of @code{strtod}, which we
do not implement, a description of the parsing is in order.  The string
is parsed as by @code{strtol}; that is, the base is recognized by
leading @samp{0} or @samp{0x} prefixes.  The number parsed is placed
in the significand such that the least significant bit of the number
is at the least significant bit of the significand.  The number is
truncated to fit the significand field provided.  The significand is
forced to be a quiet NaN@.

This function, if given a string literal all of which would have been
consumed by strtol, is evaluated early enough that it is considered a
compile-time constant.
@end deftypefn

@deftypefn {Built-in Function} _Decimal32 __builtin_nand32 (const char *str)
Similar to @code{__builtin_nan}, except the return type is @code{_Decimal32}.
@end deftypefn

@deftypefn {Built-in Function} _Decimal64 __builtin_nand64 (const char *str)
Similar to @code{__builtin_nan}, except the return type is @code{_Decimal64}.
@end deftypefn

@deftypefn {Built-in Function} _Decimal128 __builtin_nand128 (const char *str)
Similar to @code{__builtin_nan}, except the return type is @code{_Decimal128}.
@end deftypefn

@deftypefn {Built-in Function} float __builtin_nanf (const char *str)
Similar to @code{__builtin_nan}, except the return type is @code{float}.
@end deftypefn

@deftypefn {Built-in Function} {long double} __builtin_nanl (const char *str)
Similar to @code{__builtin_nan}, except the return type is @code{long double}.
@end deftypefn

@deftypefn {Built-in Function} double __builtin_nans (const char *str)
Similar to @code{__builtin_nan}, except the significand is forced
to be a signaling NaN@.  The @code{nans} function is proposed by
@uref{http://www.open-std.org/jtc1/sc22/wg14/www/docs/n965.htm,,WG14 N965}.
@end deftypefn

@deftypefn {Built-in Function} float __builtin_nansf (const char *str)
Similar to @code{__builtin_nans}, except the return type is @code{float}.
@end deftypefn

@deftypefn {Built-in Function} {long double} __builtin_nansl (const char *str)
Similar to @code{__builtin_nans}, except the return type is @code{long double}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_ffs (unsigned int x)
Returns one plus the index of the least significant 1-bit of @var{x}, or
if @var{x} is zero, returns zero.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_clz (unsigned int x)
Returns the number of leading 0-bits in @var{x}, starting at the most
significant bit position.  If @var{x} is 0, the result is undefined.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_ctz (unsigned int x)
Returns the number of trailing 0-bits in @var{x}, starting at the least
significant bit position.  If @var{x} is 0, the result is undefined.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_popcount (unsigned int x)
Returns the number of 1-bits in @var{x}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_parity (unsigned int x)
Returns the parity of @var{x}, i.e.@: the number of 1-bits in @var{x}
modulo 2.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_ffsl (unsigned long)
Similar to @code{__builtin_ffs}, except the argument type is
@code{unsigned long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_clzl (unsigned long)
Similar to @code{__builtin_clz}, except the argument type is
@code{unsigned long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_ctzl (unsigned long)
Similar to @code{__builtin_ctz}, except the argument type is
@code{unsigned long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_popcountl (unsigned long)
Similar to @code{__builtin_popcount}, except the argument type is
@code{unsigned long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_parityl (unsigned long)
Similar to @code{__builtin_parity}, except the argument type is
@code{unsigned long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_ffsll (unsigned long long)
Similar to @code{__builtin_ffs}, except the argument type is
@code{unsigned long long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_clzll (unsigned long long)
Similar to @code{__builtin_clz}, except the argument type is
@code{unsigned long long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_ctzll (unsigned long long)
Similar to @code{__builtin_ctz}, except the argument type is
@code{unsigned long long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_popcountll (unsigned long long)
Similar to @code{__builtin_popcount}, except the argument type is
@code{unsigned long long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_parityll (unsigned long long)
Similar to @code{__builtin_parity}, except the argument type is
@code{unsigned long long}.
@end deftypefn

@deftypefn {Built-in Function} double __builtin_powi (double, int)
Returns the first argument raised to the power of the second.  Unlike the
@code{pow} function no guarantees about precision and rounding are made.
@end deftypefn

@deftypefn {Built-in Function} float __builtin_powif (float, int)
Similar to @code{__builtin_powi}, except the argument and return types
are @code{float}.
@end deftypefn

@deftypefn {Built-in Function} {long double} __builtin_powil (long double, int)
Similar to @code{__builtin_powi}, except the argument and return types
are @code{long double}.
@end deftypefn


@node Target Builtins
@section Built-in Functions Specific to Particular Target Machines

On some target machines, GCC supports many built-in functions specific
to those machines.  Generally these generate calls to specific machine
instructions, but allow the compiler to schedule those calls.

@menu
* Alpha Built-in Functions::
* ARM Built-in Functions::
* Blackfin Built-in Functions::
* FR-V Built-in Functions::
* X86 Built-in Functions::
* MIPS DSP Built-in Functions::
* MIPS Paired-Single Support::
* PowerPC AltiVec Built-in Functions::
* SPARC VIS Built-in Functions::
@end menu

@node Alpha Built-in Functions
@subsection Alpha Built-in Functions

These built-in functions are available for the Alpha family of
processors, depending on the command-line switches used.

The following built-in functions are always available.  They
all generate the machine instruction that is part of the name.

@smallexample
long __builtin_alpha_implver (void)
long __builtin_alpha_rpcc (void)
long __builtin_alpha_amask (long)
long __builtin_alpha_cmpbge (long, long)
long __builtin_alpha_extbl (long, long)
long __builtin_alpha_extwl (long, long)
long __builtin_alpha_extll (long, long)
long __builtin_alpha_extql (long, long)
long __builtin_alpha_extwh (long, long)
long __builtin_alpha_extlh (long, long)
long __builtin_alpha_extqh (long, long)
long __builtin_alpha_insbl (long, long)
long __builtin_alpha_inswl (long, long)
long __builtin_alpha_insll (long, long)
long __builtin_alpha_insql (long, long)
long __builtin_alpha_inswh (long, long)
long __builtin_alpha_inslh (long, long)
long __builtin_alpha_insqh (long, long)
long __builtin_alpha_mskbl (long, long)
long __builtin_alpha_mskwl (long, long)
long __builtin_alpha_mskll (long, long)
long __builtin_alpha_mskql (long, long)
long __builtin_alpha_mskwh (long, long)
long __builtin_alpha_msklh (long, long)
long __builtin_alpha_mskqh (long, long)
long __builtin_alpha_umulh (long, long)
long __builtin_alpha_zap (long, long)
long __builtin_alpha_zapnot (long, long)
@end smallexample

The following built-in functions are always with @option{-mmax}
or @option{-mcpu=@var{cpu}} where @var{cpu} is @code{pca56} or
later.  They all generate the machine instruction that is part
of the name.

@smallexample
long __builtin_alpha_pklb (long)
long __builtin_alpha_pkwb (long)
long __builtin_alpha_unpkbl (long)
long __builtin_alpha_unpkbw (long)
long __builtin_alpha_minub8 (long, long)
long __builtin_alpha_minsb8 (long, long)
long __builtin_alpha_minuw4 (long, long)
long __builtin_alpha_minsw4 (long, long)
long __builtin_alpha_maxub8 (long, long)
long __builtin_alpha_maxsb8 (long, long)
long __builtin_alpha_maxuw4 (long, long)
long __builtin_alpha_maxsw4 (long, long)
long __builtin_alpha_perr (long, long)
@end smallexample

The following built-in functions are always with @option{-mcix}
or @option{-mcpu=@var{cpu}} where @var{cpu} is @code{ev67} or
later.  They all generate the machine instruction that is part
of the name.

@smallexample
long __builtin_alpha_cttz (long)
long __builtin_alpha_ctlz (long)
long __builtin_alpha_ctpop (long)
@end smallexample

The following builtins are available on systems that use the OSF/1
PALcode.  Normally they invoke the @code{rduniq} and @code{wruniq}
PAL calls, but when invoked with @option{-mtls-kernel}, they invoke
@code{rdval} and @code{wrval}.

@smallexample
void *__builtin_thread_pointer (void)
void __builtin_set_thread_pointer (void *)
@end smallexample

@node ARM Built-in Functions
@subsection ARM Built-in Functions

These built-in functions are available for the ARM family of
processors, when the @option{-mcpu=iwmmxt} switch is used:

@smallexample
typedef int v2si __attribute__ ((vector_size (8)));
typedef short v4hi __attribute__ ((vector_size (8)));
typedef char v8qi __attribute__ ((vector_size (8)));

int __builtin_arm_getwcx (int)
void __builtin_arm_setwcx (int, int)
int __builtin_arm_textrmsb (v8qi, int)
int __builtin_arm_textrmsh (v4hi, int)
int __builtin_arm_textrmsw (v2si, int)
int __builtin_arm_textrmub (v8qi, int)
int __builtin_arm_textrmuh (v4hi, int)
int __builtin_arm_textrmuw (v2si, int)
v8qi __builtin_arm_tinsrb (v8qi, int)
v4hi __builtin_arm_tinsrh (v4hi, int)
v2si __builtin_arm_tinsrw (v2si, int)
long long __builtin_arm_tmia (long long, int, int)
long long __builtin_arm_tmiabb (long long, int, int)
long long __builtin_arm_tmiabt (long long, int, int)
long long __builtin_arm_tmiaph (long long, int, int)
long long __builtin_arm_tmiatb (long long, int, int)
long long __builtin_arm_tmiatt (long long, int, int)
int __builtin_arm_tmovmskb (v8qi)
int __builtin_arm_tmovmskh (v4hi)
int __builtin_arm_tmovmskw (v2si)
long long __builtin_arm_waccb (v8qi)
long long __builtin_arm_wacch (v4hi)
long long __builtin_arm_waccw (v2si)
v8qi __builtin_arm_waddb (v8qi, v8qi)
v8qi __builtin_arm_waddbss (v8qi, v8qi)
v8qi __builtin_arm_waddbus (v8qi, v8qi)
v4hi __builtin_arm_waddh (v4hi, v4hi)
v4hi __builtin_arm_waddhss (v4hi, v4hi)
v4hi __builtin_arm_waddhus (v4hi, v4hi)
v2si __builtin_arm_waddw (v2si, v2si)
v2si __builtin_arm_waddwss (v2si, v2si)
v2si __builtin_arm_waddwus (v2si, v2si)
v8qi __builtin_arm_walign (v8qi, v8qi, int)
long long __builtin_arm_wand(long long, long long)
long long __builtin_arm_wandn (long long, long long)
v8qi __builtin_arm_wavg2b (v8qi, v8qi)
v8qi __builtin_arm_wavg2br (v8qi, v8qi)
v4hi __builtin_arm_wavg2h (v4hi, v4hi)
v4hi __builtin_arm_wavg2hr (v4hi, v4hi)
v8qi __builtin_arm_wcmpeqb (v8qi, v8qi)
v4hi __builtin_arm_wcmpeqh (v4hi, v4hi)
v2si __builtin_arm_wcmpeqw (v2si, v2si)
v8qi __builtin_arm_wcmpgtsb (v8qi, v8qi)
v4hi __builtin_arm_wcmpgtsh (v4hi, v4hi)
v2si __builtin_arm_wcmpgtsw (v2si, v2si)
v8qi __builtin_arm_wcmpgtub (v8qi, v8qi)
v4hi __builtin_arm_wcmpgtuh (v4hi, v4hi)
v2si __builtin_arm_wcmpgtuw (v2si, v2si)
long long __builtin_arm_wmacs (long long, v4hi, v4hi)
long long __builtin_arm_wmacsz (v4hi, v4hi)
long long __builtin_arm_wmacu (long long, v4hi, v4hi)
long long __builtin_arm_wmacuz (v4hi, v4hi)
v4hi __builtin_arm_wmadds (v4hi, v4hi)
v4hi __builtin_arm_wmaddu (v4hi, v4hi)
v8qi __builtin_arm_wmaxsb (v8qi, v8qi)
v4hi __builtin_arm_wmaxsh (v4hi, v4hi)
v2si __builtin_arm_wmaxsw (v2si, v2si)
v8qi __builtin_arm_wmaxub (v8qi, v8qi)
v4hi __builtin_arm_wmaxuh (v4hi, v4hi)
v2si __builtin_arm_wmaxuw (v2si, v2si)
v8qi __builtin_arm_wminsb (v8qi, v8qi)
v4hi __builtin_arm_wminsh (v4hi, v4hi)
v2si __builtin_arm_wminsw (v2si, v2si)
v8qi __builtin_arm_wminub (v8qi, v8qi)
v4hi __builtin_arm_wminuh (v4hi, v4hi)
v2si __builtin_arm_wminuw (v2si, v2si)
v4hi __builtin_arm_wmulsm (v4hi, v4hi)
v4hi __builtin_arm_wmulul (v4hi, v4hi)
v4hi __builtin_arm_wmulum (v4hi, v4hi)
long long __builtin_arm_wor (long long, long long)
v2si __builtin_arm_wpackdss (long long, long long)
v2si __builtin_arm_wpackdus (long long, long long)
v8qi __builtin_arm_wpackhss (v4hi, v4hi)
v8qi __builtin_arm_wpackhus (v4hi, v4hi)
v4hi __builtin_arm_wpackwss (v2si, v2si)
v4hi __builtin_arm_wpackwus (v2si, v2si)
long long __builtin_arm_wrord (long long, long long)
long long __builtin_arm_wrordi (long long, int)
v4hi __builtin_arm_wrorh (v4hi, long long)
v4hi __builtin_arm_wrorhi (v4hi, int)
v2si __builtin_arm_wrorw (v2si, long long)
v2si __builtin_arm_wrorwi (v2si, int)
v2si __builtin_arm_wsadb (v8qi, v8qi)
v2si __builtin_arm_wsadbz (v8qi, v8qi)
v2si __builtin_arm_wsadh (v4hi, v4hi)
v2si __builtin_arm_wsadhz (v4hi, v4hi)
v4hi __builtin_arm_wshufh (v4hi, int)
long long __builtin_arm_wslld (long long, long long)
long long __builtin_arm_wslldi (long long, int)
v4hi __builtin_arm_wsllh (v4hi, long long)
v4hi __builtin_arm_wsllhi (v4hi, int)
v2si __builtin_arm_wsllw (v2si, long long)
v2si __builtin_arm_wsllwi (v2si, int)
long long __builtin_arm_wsrad (long long, long long)
long long __builtin_arm_wsradi (long long, int)
v4hi __builtin_arm_wsrah (v4hi, long long)
v4hi __builtin_arm_wsrahi (v4hi, int)
v2si __builtin_arm_wsraw (v2si, long long)
v2si __builtin_arm_wsrawi (v2si, int)
long long __builtin_arm_wsrld (long long, long long)
long long __builtin_arm_wsrldi (long long, int)
v4hi __builtin_arm_wsrlh (v4hi, long long)
v4hi __builtin_arm_wsrlhi (v4hi, int)
v2si __builtin_arm_wsrlw (v2si, long long)
v2si __builtin_arm_wsrlwi (v2si, int)
v8qi __builtin_arm_wsubb (v8qi, v8qi)
v8qi __builtin_arm_wsubbss (v8qi, v8qi)
v8qi __builtin_arm_wsubbus (v8qi, v8qi)
v4hi __builtin_arm_wsubh (v4hi, v4hi)
v4hi __builtin_arm_wsubhss (v4hi, v4hi)
v4hi __builtin_arm_wsubhus (v4hi, v4hi)
v2si __builtin_arm_wsubw (v2si, v2si)
v2si __builtin_arm_wsubwss (v2si, v2si)
v2si __builtin_arm_wsubwus (v2si, v2si)
v4hi __builtin_arm_wunpckehsb (v8qi)
v2si __builtin_arm_wunpckehsh (v4hi)
long long __builtin_arm_wunpckehsw (v2si)
v4hi __builtin_arm_wunpckehub (v8qi)
v2si __builtin_arm_wunpckehuh (v4hi)
long long __builtin_arm_wunpckehuw (v2si)
v4hi __builtin_arm_wunpckelsb (v8qi)
v2si __builtin_arm_wunpckelsh (v4hi)
long long __builtin_arm_wunpckelsw (v2si)
v4hi __builtin_arm_wunpckelub (v8qi)
v2si __builtin_arm_wunpckeluh (v4hi)
long long __builtin_arm_wunpckeluw (v2si)
v8qi __builtin_arm_wunpckihb (v8qi, v8qi)
v4hi __builtin_arm_wunpckihh (v4hi, v4hi)
v2si __builtin_arm_wunpckihw (v2si, v2si)
v8qi __builtin_arm_wunpckilb (v8qi, v8qi)
v4hi __builtin_arm_wunpckilh (v4hi, v4hi)
v2si __builtin_arm_wunpckilw (v2si, v2si)
long long __builtin_arm_wxor (long long, long long)
long long __builtin_arm_wzero ()
@end smallexample

@node Blackfin Built-in Functions
@subsection Blackfin Built-in Functions

Currently, there are two Blackfin-specific built-in functions.  These are
used for generating @code{CSYNC} and @code{SSYNC} machine insns without
using inline assembly; by using these built-in functions the compiler can
automatically add workarounds for hardware errata involving these
instructions.  These functions are named as follows:

@smallexample
void __builtin_bfin_csync (void)
void __builtin_bfin_ssync (void)
@end smallexample

@node FR-V Built-in Functions
@subsection FR-V Built-in Functions

GCC provides many FR-V-specific built-in functions.  In general,
these functions are intended to be compatible with those described
by @cite{FR-V Family, Softune C/C++ Compiler Manual (V6), Fujitsu
Semiconductor}.  The two exceptions are @code{__MDUNPACKH} and
@code{__MBTOHE}, the gcc forms of which pass 128-bit values by
pointer rather than by value.

Most of the functions are named after specific FR-V instructions.
Such functions are said to be ``directly mapped'' and are summarized
here in tabular form.

@menu
* Argument Types::
* Directly-mapped Integer Functions::
* Directly-mapped Media Functions::
* Raw read/write Functions::
* Other Built-in Functions::
@end menu

@node Argument Types
@subsubsection Argument Types

The arguments to the built-in functions can be divided into three groups:
register numbers, compile-time constants and run-time values.  In order
to make this classification clear at a glance, the arguments and return
values are given the following pseudo types:

@multitable @columnfractions .20 .30 .15 .35
@item Pseudo type @tab Real C type @tab Constant? @tab Description
@item @code{uh} @tab @code{unsigned short} @tab No @tab an unsigned halfword
@item @code{uw1} @tab @code{unsigned int} @tab No @tab an unsigned word
@item @code{sw1} @tab @code{int} @tab No @tab a signed word
@item @code{uw2} @tab @code{unsigned long long} @tab No
@tab an unsigned doubleword
@item @code{sw2} @tab @code{long long} @tab No @tab a signed doubleword
@item @code{const} @tab @code{int} @tab Yes @tab an integer constant
@item @code{acc} @tab @code{int} @tab Yes @tab an ACC register number
@item @code{iacc} @tab @code{int} @tab Yes @tab an IACC register number
@end multitable

These pseudo types are not defined by GCC, they are simply a notational
convenience used in this manual.

Arguments of type @code{uh}, @code{uw1}, @code{sw1}, @code{uw2}
and @code{sw2} are evaluated at run time.  They correspond to
register operands in the underlying FR-V instructions.

@code{const} arguments represent immediate operands in the underlying
FR-V instructions.  They must be compile-time constants.

@code{acc} arguments are evaluated at compile time and specify the number
of an accumulator register.  For example, an @code{acc} argument of 2
will select the ACC2 register.

@code{iacc} arguments are similar to @code{acc} arguments but specify the
number of an IACC register.  See @pxref{Other Built-in Functions}
for more details.

@node Directly-mapped Integer Functions
@subsubsection Directly-mapped Integer Functions

The functions listed below map directly to FR-V I-type instructions.

@multitable @columnfractions .45 .32 .23
@item Function prototype @tab Example usage @tab Assembly output
@item @code{sw1 __ADDSS (sw1, sw1)}
@tab @code{@var{c} = __ADDSS (@var{a}, @var{b})}
@tab @code{ADDSS @var{a},@var{b},@var{c}}
@item @code{sw1 __SCAN (sw1, sw1)}
@tab @code{@var{c} = __SCAN (@var{a}, @var{b})}
@tab @code{SCAN @var{a},@var{b},@var{c}}
@item @code{sw1 __SCUTSS (sw1)}
@tab @code{@var{b} = __SCUTSS (@var{a})}
@tab @code{SCUTSS @var{a},@var{b}}
@item @code{sw1 __SLASS (sw1, sw1)}
@tab @code{@var{c} = __SLASS (@var{a}, @var{b})}
@tab @code{SLASS @var{a},@var{b},@var{c}}
@item @code{void __SMASS (sw1, sw1)}
@tab @code{__SMASS (@var{a}, @var{b})}
@tab @code{SMASS @var{a},@var{b}}
@item @code{void __SMSSS (sw1, sw1)}
@tab @code{__SMSSS (@var{a}, @var{b})}
@tab @code{SMSSS @var{a},@var{b}}
@item @code{void __SMU (sw1, sw1)}
@tab @code{__SMU (@var{a}, @var{b})}
@tab @code{SMU @var{a},@var{b}}
@item @code{sw2 __SMUL (sw1, sw1)}
@tab @code{@var{c} = __SMUL (@var{a}, @var{b})}
@tab @code{SMUL @var{a},@var{b},@var{c}}
@item @code{sw1 __SUBSS (sw1, sw1)}
@tab @code{@var{c} = __SUBSS (@var{a}, @var{b})}
@tab @code{SUBSS @var{a},@var{b},@var{c}}
@item @code{uw2 __UMUL (uw1, uw1)}
@tab @code{@var{c} = __UMUL (@var{a}, @var{b})}
@tab @code{UMUL @var{a},@var{b},@var{c}}
@end multitable

@node Directly-mapped Media Functions
@subsubsection Directly-mapped Media Functions

The functions listed below map directly to FR-V M-type instructions.

@multitable @columnfractions .45 .32 .23
@item Function prototype @tab Example usage @tab Assembly output
@item @code{uw1 __MABSHS (sw1)}
@tab @code{@var{b} = __MABSHS (@var{a})}
@tab @code{MABSHS @var{a},@var{b}}
@item @code{void __MADDACCS (acc, acc)}
@tab @code{__MADDACCS (@var{b}, @var{a})}
@tab @code{MADDACCS @var{a},@var{b}}
@item @code{sw1 __MADDHSS (sw1, sw1)}
@tab @code{@var{c} = __MADDHSS (@var{a}, @var{b})}
@tab @code{MADDHSS @var{a},@var{b},@var{c}}
@item @code{uw1 __MADDHUS (uw1, uw1)}
@tab @code{@var{c} = __MADDHUS (@var{a}, @var{b})}
@tab @code{MADDHUS @var{a},@var{b},@var{c}}
@item @code{uw1 __MAND (uw1, uw1)}
@tab @code{@var{c} = __MAND (@var{a}, @var{b})}
@tab @code{MAND @var{a},@var{b},@var{c}}
@item @code{void __MASACCS (acc, acc)}
@tab @code{__MASACCS (@var{b}, @var{a})}
@tab @code{MASACCS @var{a},@var{b}}
@item @code{uw1 __MAVEH (uw1, uw1)}
@tab @code{@var{c} = __MAVEH (@var{a}, @var{b})}
@tab @code{MAVEH @var{a},@var{b},@var{c}}
@item @code{uw2 __MBTOH (uw1)}
@tab @code{@var{b} = __MBTOH (@var{a})}
@tab @code{MBTOH @var{a},@var{b}}
@item @code{void __MBTOHE (uw1 *, uw1)}
@tab @code{__MBTOHE (&@var{b}, @var{a})}
@tab @code{MBTOHE @var{a},@var{b}}
@item @code{void __MCLRACC (acc)}
@tab @code{__MCLRACC (@var{a})}
@tab @code{MCLRACC @var{a}}
@item @code{void __MCLRACCA (void)}
@tab @code{__MCLRACCA ()}
@tab @code{MCLRACCA}
@item @code{uw1 __Mcop1 (uw1, uw1)}
@tab @code{@var{c} = __Mcop1 (@var{a}, @var{b})}
@tab @code{Mcop1 @var{a},@var{b},@var{c}}
@item @code{uw1 __Mcop2 (uw1, uw1)}
@tab @code{@var{c} = __Mcop2 (@var{a}, @var{b})}
@tab @code{Mcop2 @var{a},@var{b},@var{c}}
@item @code{uw1 __MCPLHI (uw2, const)}
@tab @code{@var{c} = __MCPLHI (@var{a}, @var{b})}
@tab @code{MCPLHI @var{a},#@var{b},@var{c}}
@item @code{uw1 __MCPLI (uw2, const)}
@tab @code{@var{c} = __MCPLI (@var{a}, @var{b})}
@tab @code{MCPLI @var{a},#@var{b},@var{c}}
@item @code{void __MCPXIS (acc, sw1, sw1)}
@tab @code{__MCPXIS (@var{c}, @var{a}, @var{b})}
@tab @code{MCPXIS @var{a},@var{b},@var{c}}
@item @code{void __MCPXIU (acc, uw1, uw1)}
@tab @code{__MCPXIU (@var{c}, @var{a}, @var{b})}
@tab @code{MCPXIU @var{a},@var{b},@var{c}}
@item @code{void __MCPXRS (acc, sw1, sw1)}
@tab @code{__MCPXRS (@var{c}, @var{a}, @var{b})}
@tab @code{MCPXRS @var{a},@var{b},@var{c}}
@item @code{void __MCPXRU (acc, uw1, uw1)}
@tab @code{__MCPXRU (@var{c}, @var{a}, @var{b})}
@tab @code{MCPXRU @var{a},@var{b},@var{c}}
@item @code{uw1 __MCUT (acc, uw1)}
@tab @code{@var{c} = __MCUT (@var{a}, @var{b})}
@tab @code{MCUT @var{a},@var{b},@var{c}}
@item @code{uw1 __MCUTSS (acc, sw1)}
@tab @code{@var{c} = __MCUTSS (@var{a}, @var{b})}
@tab @code{MCUTSS @var{a},@var{b},@var{c}}
@item @code{void __MDADDACCS (acc, acc)}
@tab @code{__MDADDACCS (@var{b}, @var{a})}
@tab @code{MDADDACCS @var{a},@var{b}}
@item @code{void __MDASACCS (acc, acc)}
@tab @code{__MDASACCS (@var{b}, @var{a})}
@tab @code{MDASACCS @var{a},@var{b}}
@item @code{uw2 __MDCUTSSI (acc, const)}
@tab @code{@var{c} = __MDCUTSSI (@var{a}, @var{b})}
@tab @code{MDCUTSSI @var{a},#@var{b},@var{c}}
@item @code{uw2 __MDPACKH (uw2, uw2)}
@tab @code{@var{c} = __MDPACKH (@var{a}, @var{b})}
@tab @code{MDPACKH @var{a},@var{b},@var{c}}
@item @code{uw2 __MDROTLI (uw2, const)}
@tab @code{@var{c} = __MDROTLI (@var{a}, @var{b})}
@tab @code{MDROTLI @var{a},#@var{b},@var{c}}
@item @code{void __MDSUBACCS (acc, acc)}
@tab @code{__MDSUBACCS (@var{b}, @var{a})}
@tab @code{MDSUBACCS @var{a},@var{b}}
@item @code{void __MDUNPACKH (uw1 *, uw2)}
@tab @code{__MDUNPACKH (&@var{b}, @var{a})}
@tab @code{MDUNPACKH @var{a},@var{b}}
@item @code{uw2 __MEXPDHD (uw1, const)}
@tab @code{@var{c} = __MEXPDHD (@var{a}, @var{b})}
@tab @code{MEXPDHD @var{a},#@var{b},@var{c}}
@item @code{uw1 __MEXPDHW (uw1, const)}
@tab @code{@var{c} = __MEXPDHW (@var{a}, @var{b})}
@tab @code{MEXPDHW @var{a},#@var{b},@var{c}}
@item @code{uw1 __MHDSETH (uw1, const)}
@tab @code{@var{c} = __MHDSETH (@var{a}, @var{b})}
@tab @code{MHDSETH @var{a},#@var{b},@var{c}}
@item @code{sw1 __MHDSETS (const)}
@tab @code{@var{b} = __MHDSETS (@var{a})}
@tab @code{MHDSETS #@var{a},@var{b}}
@item @code{uw1 __MHSETHIH (uw1, const)}
@tab @code{@var{b} = __MHSETHIH (@var{b}, @var{a})}
@tab @code{MHSETHIH #@var{a},@var{b}}
@item @code{sw1 __MHSETHIS (sw1, const)}
@tab @code{@var{b} = __MHSETHIS (@var{b}, @var{a})}
@tab @code{MHSETHIS #@var{a},@var{b}}
@item @code{uw1 __MHSETLOH (uw1, const)}
@tab @code{@var{b} = __MHSETLOH (@var{b}, @var{a})}
@tab @code{MHSETLOH #@var{a},@var{b}}
@item @code{sw1 __MHSETLOS (sw1, const)}
@tab @code{@var{b} = __MHSETLOS (@var{b}, @var{a})}
@tab @code{MHSETLOS #@var{a},@var{b}}
@item @code{uw1 __MHTOB (uw2)}
@tab @code{@var{b} = __MHTOB (@var{a})}
@tab @code{MHTOB @var{a},@var{b}}
@item @code{void __MMACHS (acc, sw1, sw1)}
@tab @code{__MMACHS (@var{c}, @var{a}, @var{b})}
@tab @code{MMACHS @var{a},@var{b},@var{c}}
@item @code{void __MMACHU (acc, uw1, uw1)}
@tab @code{__MMACHU (@var{c}, @var{a}, @var{b})}
@tab @code{MMACHU @var{a},@var{b},@var{c}}
@item @code{void __MMRDHS (acc, sw1, sw1)}
@tab @code{__MMRDHS (@var{c}, @var{a}, @var{b})}
@tab @code{MMRDHS @var{a},@var{b},@var{c}}
@item @code{void __MMRDHU (acc, uw1, uw1)}
@tab @code{__MMRDHU (@var{c}, @var{a}, @var{b})}
@tab @code{MMRDHU @var{a},@var{b},@var{c}}
@item @code{void __MMULHS (acc, sw1, sw1)}
@tab @code{__MMULHS (@var{c}, @var{a}, @var{b})}
@tab @code{MMULHS @var{a},@var{b},@var{c}}
@item @code{void __MMULHU (acc, uw1, uw1)}
@tab @code{__MMULHU (@var{c}, @var{a}, @var{b})}
@tab @code{MMULHU @var{a},@var{b},@var{c}}
@item @code{void __MMULXHS (acc, sw1, sw1)}
@tab @code{__MMULXHS (@var{c}, @var{a}, @var{b})}
@tab @code{MMULXHS @var{a},@var{b},@var{c}}
@item @code{void __MMULXHU (acc, uw1, uw1)}
@tab @code{__MMULXHU (@var{c}, @var{a}, @var{b})}
@tab @code{MMULXHU @var{a},@var{b},@var{c}}
@item @code{uw1 __MNOT (uw1)}
@tab @code{@var{b} = __MNOT (@var{a})}
@tab @code{MNOT @var{a},@var{b}}
@item @code{uw1 __MOR (uw1, uw1)}
@tab @code{@var{c} = __MOR (@var{a}, @var{b})}
@tab @code{MOR @var{a},@var{b},@var{c}}
@item @code{uw1 __MPACKH (uh, uh)}
@tab @code{@var{c} = __MPACKH (@var{a}, @var{b})}
@tab @code{MPACKH @var{a},@var{b},@var{c}}
@item @code{sw2 __MQADDHSS (sw2, sw2)}
@tab @code{@var{c} = __MQADDHSS (@var{a}, @var{b})}
@tab @code{MQADDHSS @var{a},@var{b},@var{c}}
@item @code{uw2 __MQADDHUS (uw2, uw2)}
@tab @code{@var{c} = __MQADDHUS (@var{a}, @var{b})}
@tab @code{MQADDHUS @var{a},@var{b},@var{c}}
@item @code{void __MQCPXIS (acc, sw2, sw2)}
@tab @code{__MQCPXIS (@var{c}, @var{a}, @var{b})}
@tab @code{MQCPXIS @var{a},@var{b},@var{c}}
@item @code{void __MQCPXIU (acc, uw2, uw2)}
@tab @code{__MQCPXIU (@var{c}, @var{a}, @var{b})}
@tab @code{MQCPXIU @var{a},@var{b},@var{c}}
@item @code{void __MQCPXRS (acc, sw2, sw2)}
@tab @code{__MQCPXRS (@var{c}, @var{a}, @var{b})}
@tab @code{MQCPXRS @var{a},@var{b},@var{c}}
@item @code{void __MQCPXRU (acc, uw2, uw2)}
@tab @code{__MQCPXRU (@var{c}, @var{a}, @var{b})}
@tab @code{MQCPXRU @var{a},@var{b},@var{c}}
@item @code{sw2 __MQLCLRHS (sw2, sw2)}
@tab @code{@var{c} = __MQLCLRHS (@var{a}, @var{b})}
@tab @code{MQLCLRHS @var{a},@var{b},@var{c}}
@item @code{sw2 __MQLMTHS (sw2, sw2)}
@tab @code{@var{c} = __MQLMTHS (@var{a}, @var{b})}
@tab @code{MQLMTHS @var{a},@var{b},@var{c}}
@item @code{void __MQMACHS (acc, sw2, sw2)}
@tab @code{__MQMACHS (@var{c}, @var{a}, @var{b})}
@tab @code{MQMACHS @var{a},@var{b},@var{c}}
@item @code{void __MQMACHU (acc, uw2, uw2)}
@tab @code{__MQMACHU (@var{c}, @var{a}, @var{b})}
@tab @code{MQMACHU @var{a},@var{b},@var{c}}
@item @code{void __MQMACXHS (acc, sw2, sw2)}
@tab @code{__MQMACXHS (@var{c}, @var{a}, @var{b})}
@tab @code{MQMACXHS @var{a},@var{b},@var{c}}
@item @code{void __MQMULHS (acc, sw2, sw2)}
@tab @code{__MQMULHS (@var{c}, @var{a}, @var{b})}
@tab @code{MQMULHS @var{a},@var{b},@var{c}}
@item @code{void __MQMULHU (acc, uw2, uw2)}
@tab @code{__MQMULHU (@var{c}, @var{a}, @var{b})}
@tab @code{MQMULHU @var{a},@var{b},@var{c}}
@item @code{void __MQMULXHS (acc, sw2, sw2)}
@tab @code{__MQMULXHS (@var{c}, @var{a}, @var{b})}
@tab @code{MQMULXHS @var{a},@var{b},@var{c}}
@item @code{void __MQMULXHU (acc, uw2, uw2)}
@tab @code{__MQMULXHU (@var{c}, @var{a}, @var{b})}
@tab @code{MQMULXHU @var{a},@var{b},@var{c}}
@item @code{sw2 __MQSATHS (sw2, sw2)}
@tab @code{@var{c} = __MQSATHS (@var{a}, @var{b})}
@tab @code{MQSATHS @var{a},@var{b},@var{c}}
@item @code{uw2 __MQSLLHI (uw2, int)}
@tab @code{@var{c} = __MQSLLHI (@var{a}, @var{b})}
@tab @code{MQSLLHI @var{a},@var{b},@var{c}}
@item @code{sw2 __MQSRAHI (sw2, int)}
@tab @code{@var{c} = __MQSRAHI (@var{a}, @var{b})}
@tab @code{MQSRAHI @var{a},@var{b},@var{c}}
@item @code{sw2 __MQSUBHSS (sw2, sw2)}
@tab @code{@var{c} = __MQSUBHSS (@var{a}, @var{b})}
@tab @code{MQSUBHSS @var{a},@var{b},@var{c}}
@item @code{uw2 __MQSUBHUS (uw2, uw2)}
@tab @code{@var{c} = __MQSUBHUS (@var{a}, @var{b})}
@tab @code{MQSUBHUS @var{a},@var{b},@var{c}}
@item @code{void __MQXMACHS (acc, sw2, sw2)}
@tab @code{__MQXMACHS (@var{c}, @var{a}, @var{b})}
@tab @code{MQXMACHS @var{a},@var{b},@var{c}}
@item @code{void __MQXMACXHS (acc, sw2, sw2)}
@tab @code{__MQXMACXHS (@var{c}, @var{a}, @var{b})}
@tab @code{MQXMACXHS @var{a},@var{b},@var{c}}
@item @code{uw1 __MRDACC (acc)}
@tab @code{@var{b} = __MRDACC (@var{a})}
@tab @code{MRDACC @var{a},@var{b}}
@item @code{uw1 __MRDACCG (acc)}
@tab @code{@var{b} = __MRDACCG (@var{a})}
@tab @code{MRDACCG @var{a},@var{b}}
@item @code{uw1 __MROTLI (uw1, const)}
@tab @code{@var{c} = __MROTLI (@var{a}, @var{b})}
@tab @code{MROTLI @var{a},#@var{b},@var{c}}
@item @code{uw1 __MROTRI (uw1, const)}
@tab @code{@var{c} = __MROTRI (@var{a}, @var{b})}
@tab @code{MROTRI @var{a},#@var{b},@var{c}}
@item @code{sw1 __MSATHS (sw1, sw1)}
@tab @code{@var{c} = __MSATHS (@var{a}, @var{b})}
@tab @code{MSATHS @var{a},@var{b},@var{c}}
@item @code{uw1 __MSATHU (uw1, uw1)}
@tab @code{@var{c} = __MSATHU (@var{a}, @var{b})}
@tab @code{MSATHU @var{a},@var{b},@var{c}}
@item @code{uw1 __MSLLHI (uw1, const)}
@tab @code{@var{c} = __MSLLHI (@var{a}, @var{b})}
@tab @code{MSLLHI @var{a},#@var{b},@var{c}}
@item @code{sw1 __MSRAHI (sw1, const)}
@tab @code{@var{c} = __MSRAHI (@var{a}, @var{b})}
@tab @code{MSRAHI @var{a},#@var{b},@var{c}}
@item @code{uw1 __MSRLHI (uw1, const)}
@tab @code{@var{c} = __MSRLHI (@var{a}, @var{b})}
@tab @code{MSRLHI @var{a},#@var{b},@var{c}}
@item @code{void __MSUBACCS (acc, acc)}
@tab @code{__MSUBACCS (@var{b}, @var{a})}
@tab @code{MSUBACCS @var{a},@var{b}}
@item @code{sw1 __MSUBHSS (sw1, sw1)}
@tab @code{@var{c} = __MSUBHSS (@var{a}, @var{b})}
@tab @code{MSUBHSS @var{a},@var{b},@var{c}}
@item @code{uw1 __MSUBHUS (uw1, uw1)}
@tab @code{@var{c} = __MSUBHUS (@var{a}, @var{b})}
@tab @code{MSUBHUS @var{a},@var{b},@var{c}}
@item @code{void __MTRAP (void)}
@tab @code{__MTRAP ()}
@tab @code{MTRAP}
@item @code{uw2 __MUNPACKH (uw1)}
@tab @code{@var{b} = __MUNPACKH (@var{a})}
@tab @code{MUNPACKH @var{a},@var{b}}
@item @code{uw1 __MWCUT (uw2, uw1)}
@tab @code{@var{c} = __MWCUT (@var{a}, @var{b})}
@tab @code{MWCUT @var{a},@var{b},@var{c}}
@item @code{void __MWTACC (acc, uw1)}
@tab @code{__MWTACC (@var{b}, @var{a})}
@tab @code{MWTACC @var{a},@var{b}}
@item @code{void __MWTACCG (acc, uw1)}
@tab @code{__MWTACCG (@var{b}, @var{a})}
@tab @code{MWTACCG @var{a},@var{b}}
@item @code{uw1 __MXOR (uw1, uw1)}
@tab @code{@var{c} = __MXOR (@var{a}, @var{b})}
@tab @code{MXOR @var{a},@var{b},@var{c}}
@end multitable

@node Raw read/write Functions
@subsubsection Raw read/write Functions

This sections describes built-in functions related to read and write
instructions to access memory.  These functions generate
@code{membar} instructions to flush the I/O load and stores where
appropriate, as described in Fujitsu's manual described above.

@table @code

@item unsigned char __builtin_read8 (void *@var{data})
@item unsigned short __builtin_read16 (void *@var{data})
@item unsigned long __builtin_read32 (void *@var{data})
@item unsigned long long __builtin_read64 (void *@var{data})

@item void __builtin_write8 (void *@var{data}, unsigned char @var{datum})
@item void __builtin_write16 (void *@var{data}, unsigned short @var{datum})
@item void __builtin_write32 (void *@var{data}, unsigned long @var{datum})
@item void __builtin_write64 (void *@var{data}, unsigned long long @var{datum})
@end table

@node Other Built-in Functions
@subsubsection Other Built-in Functions

This section describes built-in functions that are not named after
a specific FR-V instruction.

@table @code
@item sw2 __IACCreadll (iacc @var{reg})
Return the full 64-bit value of IACC0@.  The @var{reg} argument is reserved
for future expansion and must be 0.

@item sw1 __IACCreadl (iacc @var{reg})
Return the value of IACC0H if @var{reg} is 0 and IACC0L if @var{reg} is 1.
Other values of @var{reg} are rejected as invalid.

@item void __IACCsetll (iacc @var{reg}, sw2 @var{x})
Set the full 64-bit value of IACC0 to @var{x}.  The @var{reg} argument
is reserved for future expansion and must be 0.

@item void __IACCsetl (iacc @var{reg}, sw1 @var{x})
Set IACC0H to @var{x} if @var{reg} is 0 and IACC0L to @var{x} if @var{reg}
is 1.  Other values of @var{reg} are rejected as invalid.

@item void __data_prefetch0 (const void *@var{x})
Use the @code{dcpl} instruction to load the contents of address @var{x}
into the data cache.

@item void __data_prefetch (const void *@var{x})
Use the @code{nldub} instruction to load the contents of address @var{x}
into the data cache.  The instruction will be issued in slot I1@.
@end table

@node X86 Built-in Functions
@subsection X86 Built-in Functions

These built-in functions are available for the i386 and x86-64 family
of computers, depending on the command-line switches used.

Note that, if you specify command-line switches such as @option{-msse},
the compiler could use the extended instruction sets even if the built-ins
are not used explicitly in the program.  For this reason, applications
which perform runtime CPU detection must compile separate files for each
supported architecture, using the appropriate flags.  In particular,
the file containing the CPU detection code should be compiled without
these options.

The following machine modes are available for use with MMX built-in functions
(@pxref{Vector Extensions}): @code{V2SI} for a vector of two 32-bit integers,
@code{V4HI} for a vector of four 16-bit integers, and @code{V8QI} for a
vector of eight 8-bit integers.  Some of the built-in functions operate on
MMX registers as a whole 64-bit entity, these use @code{DI} as their mode.

If 3Dnow extensions are enabled, @code{V2SF} is used as a mode for a vector
of two 32-bit floating point values.

If SSE extensions are enabled, @code{V4SF} is used for a vector of four 32-bit
floating point values.  Some instructions use a vector of four 32-bit
integers, these use @code{V4SI}.  Finally, some instructions operate on an
entire vector register, interpreting it as a 128-bit integer, these use mode
@code{TI}.

The following built-in functions are made available by @option{-mmmx}.
All of them generate the machine instruction that is part of the name.

@smallexample
v8qi __builtin_ia32_paddb (v8qi, v8qi)
v4hi __builtin_ia32_paddw (v4hi, v4hi)
v2si __builtin_ia32_paddd (v2si, v2si)
v8qi __builtin_ia32_psubb (v8qi, v8qi)
v4hi __builtin_ia32_psubw (v4hi, v4hi)
v2si __builtin_ia32_psubd (v2si, v2si)
v8qi __builtin_ia32_paddsb (v8qi, v8qi)
v4hi __builtin_ia32_paddsw (v4hi, v4hi)
v8qi __builtin_ia32_psubsb (v8qi, v8qi)
v4hi __builtin_ia32_psubsw (v4hi, v4hi)
v8qi __builtin_ia32_paddusb (v8qi, v8qi)
v4hi __builtin_ia32_paddusw (v4hi, v4hi)
v8qi __builtin_ia32_psubusb (v8qi, v8qi)
v4hi __builtin_ia32_psubusw (v4hi, v4hi)
v4hi __builtin_ia32_pmullw (v4hi, v4hi)
v4hi __builtin_ia32_pmulhw (v4hi, v4hi)
di __builtin_ia32_pand (di, di)
di __builtin_ia32_pandn (di,di)
di __builtin_ia32_por (di, di)
di __builtin_ia32_pxor (di, di)
v8qi __builtin_ia32_pcmpeqb (v8qi, v8qi)
v4hi __builtin_ia32_pcmpeqw (v4hi, v4hi)
v2si __builtin_ia32_pcmpeqd (v2si, v2si)
v8qi __builtin_ia32_pcmpgtb (v8qi, v8qi)
v4hi __builtin_ia32_pcmpgtw (v4hi, v4hi)
v2si __builtin_ia32_pcmpgtd (v2si, v2si)
v8qi __builtin_ia32_punpckhbw (v8qi, v8qi)
v4hi __builtin_ia32_punpckhwd (v4hi, v4hi)
v2si __builtin_ia32_punpckhdq (v2si, v2si)
v8qi __builtin_ia32_punpcklbw (v8qi, v8qi)
v4hi __builtin_ia32_punpcklwd (v4hi, v4hi)
v2si __builtin_ia32_punpckldq (v2si, v2si)
v8qi __builtin_ia32_packsswb (v4hi, v4hi)
v4hi __builtin_ia32_packssdw (v2si, v2si)
v8qi __builtin_ia32_packuswb (v4hi, v4hi)
@end smallexample

The following built-in functions are made available either with
@option{-msse}, or with a combination of @option{-m3dnow} and
@option{-march=athlon}.  All of them generate the machine
instruction that is part of the name.

@smallexample
v4hi __builtin_ia32_pmulhuw (v4hi, v4hi)
v8qi __builtin_ia32_pavgb (v8qi, v8qi)
v4hi __builtin_ia32_pavgw (v4hi, v4hi)
v4hi __builtin_ia32_psadbw (v8qi, v8qi)
v8qi __builtin_ia32_pmaxub (v8qi, v8qi)
v4hi __builtin_ia32_pmaxsw (v4hi, v4hi)
v8qi __builtin_ia32_pminub (v8qi, v8qi)
v4hi __builtin_ia32_pminsw (v4hi, v4hi)
int __builtin_ia32_pextrw (v4hi, int)
v4hi __builtin_ia32_pinsrw (v4hi, int, int)
int __builtin_ia32_pmovmskb (v8qi)
void __builtin_ia32_maskmovq (v8qi, v8qi, char *)
void __builtin_ia32_movntq (di *, di)
void __builtin_ia32_sfence (void)
@end smallexample

The following built-in functions are available when @option{-msse} is used.
All of them generate the machine instruction that is part of the name.

@smallexample
int __builtin_ia32_comieq (v4sf, v4sf)
int __builtin_ia32_comineq (v4sf, v4sf)
int __builtin_ia32_comilt (v4sf, v4sf)
int __builtin_ia32_comile (v4sf, v4sf)
int __builtin_ia32_comigt (v4sf, v4sf)
int __builtin_ia32_comige (v4sf, v4sf)
int __builtin_ia32_ucomieq (v4sf, v4sf)
int __builtin_ia32_ucomineq (v4sf, v4sf)
int __builtin_ia32_ucomilt (v4sf, v4sf)
int __builtin_ia32_ucomile (v4sf, v4sf)
int __builtin_ia32_ucomigt (v4sf, v4sf)
int __builtin_ia32_ucomige (v4sf, v4sf)
v4sf __builtin_ia32_addps (v4sf, v4sf)
v4sf __builtin_ia32_subps (v4sf, v4sf)
v4sf __builtin_ia32_mulps (v4sf, v4sf)
v4sf __builtin_ia32_divps (v4sf, v4sf)
v4sf __builtin_ia32_addss (v4sf, v4sf)
v4sf __builtin_ia32_subss (v4sf, v4sf)
v4sf __builtin_ia32_mulss (v4sf, v4sf)
v4sf __builtin_ia32_divss (v4sf, v4sf)
v4si __builtin_ia32_cmpeqps (v4sf, v4sf)
v4si __builtin_ia32_cmpltps (v4sf, v4sf)
v4si __builtin_ia32_cmpleps (v4sf, v4sf)
v4si __builtin_ia32_cmpgtps (v4sf, v4sf)
v4si __builtin_ia32_cmpgeps (v4sf, v4sf)
v4si __builtin_ia32_cmpunordps (v4sf, v4sf)
v4si __builtin_ia32_cmpneqps (v4sf, v4sf)
v4si __builtin_ia32_cmpnltps (v4sf, v4sf)
v4si __builtin_ia32_cmpnleps (v4sf, v4sf)
v4si __builtin_ia32_cmpngtps (v4sf, v4sf)
v4si __builtin_ia32_cmpngeps (v4sf, v4sf)
v4si __builtin_ia32_cmpordps (v4sf, v4sf)
v4si __builtin_ia32_cmpeqss (v4sf, v4sf)
v4si __builtin_ia32_cmpltss (v4sf, v4sf)
v4si __builtin_ia32_cmpless (v4sf, v4sf)
v4si __builtin_ia32_cmpunordss (v4sf, v4sf)
v4si __builtin_ia32_cmpneqss (v4sf, v4sf)
v4si __builtin_ia32_cmpnlts (v4sf, v4sf)
v4si __builtin_ia32_cmpnless (v4sf, v4sf)
v4si __builtin_ia32_cmpordss (v4sf, v4sf)
v4sf __builtin_ia32_maxps (v4sf, v4sf)
v4sf __builtin_ia32_maxss (v4sf, v4sf)
v4sf __builtin_ia32_minps (v4sf, v4sf)
v4sf __builtin_ia32_minss (v4sf, v4sf)
v4sf __builtin_ia32_andps (v4sf, v4sf)
v4sf __builtin_ia32_andnps (v4sf, v4sf)
v4sf __builtin_ia32_orps (v4sf, v4sf)
v4sf __builtin_ia32_xorps (v4sf, v4sf)
v4sf __builtin_ia32_movss (v4sf, v4sf)
v4sf __builtin_ia32_movhlps (v4sf, v4sf)
v4sf __builtin_ia32_movlhps (v4sf, v4sf)
v4sf __builtin_ia32_unpckhps (v4sf, v4sf)
v4sf __builtin_ia32_unpcklps (v4sf, v4sf)
v4sf __builtin_ia32_cvtpi2ps (v4sf, v2si)
v4sf __builtin_ia32_cvtsi2ss (v4sf, int)
v2si __builtin_ia32_cvtps2pi (v4sf)
int __builtin_ia32_cvtss2si (v4sf)
v2si __builtin_ia32_cvttps2pi (v4sf)
int __builtin_ia32_cvttss2si (v4sf)
v4sf __builtin_ia32_rcpps (v4sf)
v4sf __builtin_ia32_rsqrtps (v4sf)
v4sf __builtin_ia32_sqrtps (v4sf)
v4sf __builtin_ia32_rcpss (v4sf)
v4sf __builtin_ia32_rsqrtss (v4sf)
v4sf __builtin_ia32_sqrtss (v4sf)
v4sf __builtin_ia32_shufps (v4sf, v4sf, int)
void __builtin_ia32_movntps (float *, v4sf)
int __builtin_ia32_movmskps (v4sf)
@end smallexample

The following built-in functions are available when @option{-msse} is used.

@table @code
@item v4sf __builtin_ia32_loadaps (float *)
Generates the @code{movaps} machine instruction as a load from memory.
@item void __builtin_ia32_storeaps (float *, v4sf)
Generates the @code{movaps} machine instruction as a store to memory.
@item v4sf __builtin_ia32_loadups (float *)
Generates the @code{movups} machine instruction as a load from memory.
@item void __builtin_ia32_storeups (float *, v4sf)
Generates the @code{movups} machine instruction as a store to memory.
@item v4sf __builtin_ia32_loadsss (float *)
Generates the @code{movss} machine instruction as a load from memory.
@item void __builtin_ia32_storess (float *, v4sf)
Generates the @code{movss} machine instruction as a store to memory.
@item v4sf __builtin_ia32_loadhps (v4sf, v2si *)
Generates the @code{movhps} machine instruction as a load from memory.
@item v4sf __builtin_ia32_loadlps (v4sf, v2si *)
Generates the @code{movlps} machine instruction as a load from memory
@item void __builtin_ia32_storehps (v4sf, v2si *)
Generates the @code{movhps} machine instruction as a store to memory.
@item void __builtin_ia32_storelps (v4sf, v2si *)
Generates the @code{movlps} machine instruction as a store to memory.
@end table

The following built-in functions are available when @option{-msse2} is used.
All of them generate the machine instruction that is part of the name.

@smallexample
int __builtin_ia32_comisdeq (v2df, v2df)
int __builtin_ia32_comisdlt (v2df, v2df)
int __builtin_ia32_comisdle (v2df, v2df)
int __builtin_ia32_comisdgt (v2df, v2df)
int __builtin_ia32_comisdge (v2df, v2df)
int __builtin_ia32_comisdneq (v2df, v2df)
int __builtin_ia32_ucomisdeq (v2df, v2df)
int __builtin_ia32_ucomisdlt (v2df, v2df)
int __builtin_ia32_ucomisdle (v2df, v2df)
int __builtin_ia32_ucomisdgt (v2df, v2df)
int __builtin_ia32_ucomisdge (v2df, v2df)
int __builtin_ia32_ucomisdneq (v2df, v2df)
v2df __builtin_ia32_cmpeqpd (v2df, v2df)
v2df __builtin_ia32_cmpltpd (v2df, v2df)
v2df __builtin_ia32_cmplepd (v2df, v2df)
v2df __builtin_ia32_cmpgtpd (v2df, v2df)
v2df __builtin_ia32_cmpgepd (v2df, v2df)
v2df __builtin_ia32_cmpunordpd (v2df, v2df)
v2df __builtin_ia32_cmpneqpd (v2df, v2df)
v2df __builtin_ia32_cmpnltpd (v2df, v2df)
v2df __builtin_ia32_cmpnlepd (v2df, v2df)
v2df __builtin_ia32_cmpngtpd (v2df, v2df)
v2df __builtin_ia32_cmpngepd (v2df, v2df)
v2df __builtin_ia32_cmpordpd (v2df, v2df)
v2df __builtin_ia32_cmpeqsd (v2df, v2df)
v2df __builtin_ia32_cmpltsd (v2df, v2df)
v2df __builtin_ia32_cmplesd (v2df, v2df)
v2df __builtin_ia32_cmpunordsd (v2df, v2df)
v2df __builtin_ia32_cmpneqsd (v2df, v2df)
v2df __builtin_ia32_cmpnltsd (v2df, v2df)
v2df __builtin_ia32_cmpnlesd (v2df, v2df)
v2df __builtin_ia32_cmpordsd (v2df, v2df)
v2di __builtin_ia32_paddq (v2di, v2di)
v2di __builtin_ia32_psubq (v2di, v2di)
v2df __builtin_ia32_addpd (v2df, v2df)
v2df __builtin_ia32_subpd (v2df, v2df)
v2df __builtin_ia32_mulpd (v2df, v2df)
v2df __builtin_ia32_divpd (v2df, v2df)
v2df __builtin_ia32_addsd (v2df, v2df)
v2df __builtin_ia32_subsd (v2df, v2df)
v2df __builtin_ia32_mulsd (v2df, v2df)
v2df __builtin_ia32_divsd (v2df, v2df)
v2df __builtin_ia32_minpd (v2df, v2df)
v2df __builtin_ia32_maxpd (v2df, v2df)
v2df __builtin_ia32_minsd (v2df, v2df)
v2df __builtin_ia32_maxsd (v2df, v2df)
v2df __builtin_ia32_andpd (v2df, v2df)
v2df __builtin_ia32_andnpd (v2df, v2df)
v2df __builtin_ia32_orpd (v2df, v2df)
v2df __builtin_ia32_xorpd (v2df, v2df)
v2df __builtin_ia32_movsd (v2df, v2df)
v2df __builtin_ia32_unpckhpd (v2df, v2df)
v2df __builtin_ia32_unpcklpd (v2df, v2df)
v16qi __builtin_ia32_paddb128 (v16qi, v16qi)
v8hi __builtin_ia32_paddw128 (v8hi, v8hi)
v4si __builtin_ia32_paddd128 (v4si, v4si)
v2di __builtin_ia32_paddq128 (v2di, v2di)
v16qi __builtin_ia32_psubb128 (v16qi, v16qi)
v8hi __builtin_ia32_psubw128 (v8hi, v8hi)
v4si __builtin_ia32_psubd128 (v4si, v4si)
v2di __builtin_ia32_psubq128 (v2di, v2di)
v8hi __builtin_ia32_pmullw128 (v8hi, v8hi)
v8hi __builtin_ia32_pmulhw128 (v8hi, v8hi)
v2di __builtin_ia32_pand128 (v2di, v2di)
v2di __builtin_ia32_pandn128 (v2di, v2di)
v2di __builtin_ia32_por128 (v2di, v2di)
v2di __builtin_ia32_pxor128 (v2di, v2di)
v16qi __builtin_ia32_pavgb128 (v16qi, v16qi)
v8hi __builtin_ia32_pavgw128 (v8hi, v8hi)
v16qi __builtin_ia32_pcmpeqb128 (v16qi, v16qi)
v8hi __builtin_ia32_pcmpeqw128 (v8hi, v8hi)
v4si __builtin_ia32_pcmpeqd128 (v4si, v4si)
v16qi __builtin_ia32_pcmpgtb128 (v16qi, v16qi)
v8hi __builtin_ia32_pcmpgtw128 (v8hi, v8hi)
v4si __builtin_ia32_pcmpgtd128 (v4si, v4si)
v16qi __builtin_ia32_pmaxub128 (v16qi, v16qi)
v8hi __builtin_ia32_pmaxsw128 (v8hi, v8hi)
v16qi __builtin_ia32_pminub128 (v16qi, v16qi)
v8hi __builtin_ia32_pminsw128 (v8hi, v8hi)
v16qi __builtin_ia32_punpckhbw128 (v16qi, v16qi)
v8hi __builtin_ia32_punpckhwd128 (v8hi, v8hi)
v4si __builtin_ia32_punpckhdq128 (v4si, v4si)
v2di __builtin_ia32_punpckhqdq128 (v2di, v2di)
v16qi __builtin_ia32_punpcklbw128 (v16qi, v16qi)
v8hi __builtin_ia32_punpcklwd128 (v8hi, v8hi)
v4si __builtin_ia32_punpckldq128 (v4si, v4si)
v2di __builtin_ia32_punpcklqdq128 (v2di, v2di)
v16qi __builtin_ia32_packsswb128 (v16qi, v16qi)
v8hi __builtin_ia32_packssdw128 (v8hi, v8hi)
v16qi __builtin_ia32_packuswb128 (v16qi, v16qi)
v8hi __builtin_ia32_pmulhuw128 (v8hi, v8hi)
void __builtin_ia32_maskmovdqu (v16qi, v16qi)
v2df __builtin_ia32_loadupd (double *)
void __builtin_ia32_storeupd (double *, v2df)
v2df __builtin_ia32_loadhpd (v2df, double *)
v2df __builtin_ia32_loadlpd (v2df, double *)
int __builtin_ia32_movmskpd (v2df)
int __builtin_ia32_pmovmskb128 (v16qi)
void __builtin_ia32_movnti (int *, int)
void __builtin_ia32_movntpd (double *, v2df)
void __builtin_ia32_movntdq (v2df *, v2df)
v4si __builtin_ia32_pshufd (v4si, int)
v8hi __builtin_ia32_pshuflw (v8hi, int)
v8hi __builtin_ia32_pshufhw (v8hi, int)
v2di __builtin_ia32_psadbw128 (v16qi, v16qi)
v2df __builtin_ia32_sqrtpd (v2df)
v2df __builtin_ia32_sqrtsd (v2df)
v2df __builtin_ia32_shufpd (v2df, v2df, int)
v2df __builtin_ia32_cvtdq2pd (v4si)
v4sf __builtin_ia32_cvtdq2ps (v4si)
v4si __builtin_ia32_cvtpd2dq (v2df)
v2si __builtin_ia32_cvtpd2pi (v2df)
v4sf __builtin_ia32_cvtpd2ps (v2df)
v4si __builtin_ia32_cvttpd2dq (v2df)
v2si __builtin_ia32_cvttpd2pi (v2df)
v2df __builtin_ia32_cvtpi2pd (v2si)
int __builtin_ia32_cvtsd2si (v2df)
int __builtin_ia32_cvttsd2si (v2df)
long long __builtin_ia32_cvtsd2si64 (v2df)
long long __builtin_ia32_cvttsd2si64 (v2df)
v4si __builtin_ia32_cvtps2dq (v4sf)
v2df __builtin_ia32_cvtps2pd (v4sf)
v4si __builtin_ia32_cvttps2dq (v4sf)
v2df __builtin_ia32_cvtsi2sd (v2df, int)
v2df __builtin_ia32_cvtsi642sd (v2df, long long)
v4sf __builtin_ia32_cvtsd2ss (v4sf, v2df)
v2df __builtin_ia32_cvtss2sd (v2df, v4sf)
void __builtin_ia32_clflush (const void *)
void __builtin_ia32_lfence (void)
void __builtin_ia32_mfence (void)
v16qi __builtin_ia32_loaddqu (const char *)
void __builtin_ia32_storedqu (char *, v16qi)
unsigned long long __builtin_ia32_pmuludq (v2si, v2si)
v2di __builtin_ia32_pmuludq128 (v4si, v4si)
v8hi __builtin_ia32_psllw128 (v8hi, v2di)
v4si __builtin_ia32_pslld128 (v4si, v2di)
v2di __builtin_ia32_psllq128 (v4si, v2di)
v8hi __builtin_ia32_psrlw128 (v8hi, v2di)
v4si __builtin_ia32_psrld128 (v4si, v2di)
v2di __builtin_ia32_psrlq128 (v2di, v2di)
v8hi __builtin_ia32_psraw128 (v8hi, v2di)
v4si __builtin_ia32_psrad128 (v4si, v2di)
v2di __builtin_ia32_pslldqi128 (v2di, int)
v8hi __builtin_ia32_psllwi128 (v8hi, int)
v4si __builtin_ia32_pslldi128 (v4si, int)
v2di __builtin_ia32_psllqi128 (v2di, int)
v2di __builtin_ia32_psrldqi128 (v2di, int)
v8hi __builtin_ia32_psrlwi128 (v8hi, int)
v4si __builtin_ia32_psrldi128 (v4si, int)
v2di __builtin_ia32_psrlqi128 (v2di, int)
v8hi __builtin_ia32_psrawi128 (v8hi, int)
v4si __builtin_ia32_psradi128 (v4si, int)
v4si __builtin_ia32_pmaddwd128 (v8hi, v8hi)
@end smallexample

The following built-in functions are available when @option{-msse3} is used.
All of them generate the machine instruction that is part of the name.

@smallexample
v2df __builtin_ia32_addsubpd (v2df, v2df)
v4sf __builtin_ia32_addsubps (v4sf, v4sf)
v2df __builtin_ia32_haddpd (v2df, v2df)
v4sf __builtin_ia32_haddps (v4sf, v4sf)
v2df __builtin_ia32_hsubpd (v2df, v2df)
v4sf __builtin_ia32_hsubps (v4sf, v4sf)
v16qi __builtin_ia32_lddqu (char const *)
void __builtin_ia32_monitor (void *, unsigned int, unsigned int)
v2df __builtin_ia32_movddup (v2df)
v4sf __builtin_ia32_movshdup (v4sf)
v4sf __builtin_ia32_movsldup (v4sf)
void __builtin_ia32_mwait (unsigned int, unsigned int)
@end smallexample

The following built-in functions are available when @option{-msse3} is used.

@table @code
@item v2df __builtin_ia32_loadddup (double const *)
Generates the @code{movddup} machine instruction as a load from memory.
@end table

The following built-in functions are available when @option{-m3dnow} is used.
All of them generate the machine instruction that is part of the name.

@smallexample
void __builtin_ia32_femms (void)
v8qi __builtin_ia32_pavgusb (v8qi, v8qi)
v2si __builtin_ia32_pf2id (v2sf)
v2sf __builtin_ia32_pfacc (v2sf, v2sf)
v2sf __builtin_ia32_pfadd (v2sf, v2sf)
v2si __builtin_ia32_pfcmpeq (v2sf, v2sf)
v2si __builtin_ia32_pfcmpge (v2sf, v2sf)
v2si __builtin_ia32_pfcmpgt (v2sf, v2sf)
v2sf __builtin_ia32_pfmax (v2sf, v2sf)
v2sf __builtin_ia32_pfmin (v2sf, v2sf)
v2sf __builtin_ia32_pfmul (v2sf, v2sf)
v2sf __builtin_ia32_pfrcp (v2sf)
v2sf __builtin_ia32_pfrcpit1 (v2sf, v2sf)
v2sf __builtin_ia32_pfrcpit2 (v2sf, v2sf)
v2sf __builtin_ia32_pfrsqrt (v2sf)
v2sf __builtin_ia32_pfrsqrtit1 (v2sf, v2sf)
v2sf __builtin_ia32_pfsub (v2sf, v2sf)
v2sf __builtin_ia32_pfsubr (v2sf, v2sf)
v2sf __builtin_ia32_pi2fd (v2si)
v4hi __builtin_ia32_pmulhrw (v4hi, v4hi)
@end smallexample

The following built-in functions are available when both @option{-m3dnow}
and @option{-march=athlon} are used.  All of them generate the machine
instruction that is part of the name.

@smallexample
v2si __builtin_ia32_pf2iw (v2sf)
v2sf __builtin_ia32_pfnacc (v2sf, v2sf)
v2sf __builtin_ia32_pfpnacc (v2sf, v2sf)
v2sf __builtin_ia32_pi2fw (v2si)
v2sf __builtin_ia32_pswapdsf (v2sf)
v2si __builtin_ia32_pswapdsi (v2si)
@end smallexample

@node MIPS DSP Built-in Functions
@subsection MIPS DSP Built-in Functions

The MIPS DSP Application-Specific Extension (ASE) includes new
instructions that are designed to improve the performance of DSP and
media applications.  It provides instructions that operate on packed
8-bit integer data, Q15 fractional data and Q31 fractional data.

GCC supports MIPS DSP operations using both the generic
vector extensions (@pxref{Vector Extensions}) and a collection of
MIPS-specific built-in functions.  Both kinds of support are
enabled by the @option{-mdsp} command-line option.

At present, GCC only provides support for operations on 32-bit
vectors.  The vector type associated with 8-bit integer data is
usually called @code{v4i8} and the vector type associated with Q15 is
usually called @code{v2q15}.  They can be defined in C as follows:

@smallexample
typedef char v4i8 __attribute__ ((vector_size(4)));
typedef short v2q15 __attribute__ ((vector_size(4)));
@end smallexample

@code{v4i8} and @code{v2q15} values are initialized in the same way as
aggregates.  For example:

@smallexample
v4i8 a = @{1, 2, 3, 4@};
v4i8 b;
b = (v4i8) @{5, 6, 7, 8@};

v2q15 c = @{0x0fcb, 0x3a75@};
v2q15 d;
d = (v2q15) @{0.1234 * 0x1.0p15, 0.4567 * 0x1.0p15@};
@end smallexample

@emph{Note:} The CPU's endianness determines the order in which values
are packed.  On little-endian targets, the first value is the least
significant and the last value is the most significant.  The opposite
order applies to big-endian targets.  For example, the code above will
set the lowest byte of @code{a} to @code{1} on little-endian targets
and @code{4} on big-endian targets.

@emph{Note:} Q15 and Q31 values must be initialized with their integer
representation.  As shown in this example, the integer representation
of a Q15 value can be obtained by multiplying the fractional value by
@code{0x1.0p15}.  The equivalent for Q31 values is to multiply by
@code{0x1.0p31}.

The table below lists the @code{v4i8} and @code{v2q15} operations for which
hardware support exists.  @code{a} and @code{b} are @code{v4i8} values,
and @code{c} and @code{d} are @code{v2q15} values.

@multitable @columnfractions .50 .50
@item C code @tab MIPS instruction
@item @code{a + b} @tab @code{addu.qb}
@item @code{c + d} @tab @code{addq.ph}
@item @code{a - b} @tab @code{subu.qb}
@item @code{c - d} @tab @code{subq.ph}
@end multitable

It is easier to describe the DSP built-in functions if we first define
the following types:

@smallexample
typedef int q31;
typedef int i32;
typedef long long a64;
@end smallexample

@code{q31} and @code{i32} are actually the same as @code{int}, but we
use @code{q31} to indicate a Q31 fractional value and @code{i32} to
indicate a 32-bit integer value.  Similarly, @code{a64} is the same as
@code{long long}, but we use @code{a64} to indicate values that will
be placed in one of the four DSP accumulators (@code{$ac0},
@code{$ac1}, @code{$ac2} or @code{$ac3}).

Also, some built-in functions prefer or require immediate numbers as
parameters, because the corresponding DSP instructions accept both immediate
numbers and register operands, or accept immediate numbers only.  The
immediate parameters are listed as follows.

@smallexample
imm0_7: 0 to 7.
imm0_15: 0 to 15.
imm0_31: 0 to 31.
imm0_63: 0 to 63.
imm0_255: 0 to 255.
imm_n32_31: -32 to 31.
imm_n512_511: -512 to 511.
@end smallexample

The following built-in functions map directly to a particular MIPS DSP
instruction.  Please refer to the architecture specification
for details on what each instruction does.

@smallexample
v2q15 __builtin_mips_addq_ph (v2q15, v2q15)
v2q15 __builtin_mips_addq_s_ph (v2q15, v2q15)
q31 __builtin_mips_addq_s_w (q31, q31)
v4i8 __builtin_mips_addu_qb (v4i8, v4i8)
v4i8 __builtin_mips_addu_s_qb (v4i8, v4i8)
v2q15 __builtin_mips_subq_ph (v2q15, v2q15)
v2q15 __builtin_mips_subq_s_ph (v2q15, v2q15)
q31 __builtin_mips_subq_s_w (q31, q31)
v4i8 __builtin_mips_subu_qb (v4i8, v4i8)
v4i8 __builtin_mips_subu_s_qb (v4i8, v4i8)
i32 __builtin_mips_addsc (i32, i32)
i32 __builtin_mips_addwc (i32, i32)
i32 __builtin_mips_modsub (i32, i32)
i32 __builtin_mips_raddu_w_qb (v4i8)
v2q15 __builtin_mips_absq_s_ph (v2q15)
q31 __builtin_mips_absq_s_w (q31)
v4i8 __builtin_mips_precrq_qb_ph (v2q15, v2q15)
v2q15 __builtin_mips_precrq_ph_w (q31, q31)
v2q15 __builtin_mips_precrq_rs_ph_w (q31, q31)
v4i8 __builtin_mips_precrqu_s_qb_ph (v2q15, v2q15)
q31 __builtin_mips_preceq_w_phl (v2q15)
q31 __builtin_mips_preceq_w_phr (v2q15)
v2q15 __builtin_mips_precequ_ph_qbl (v4i8)
v2q15 __builtin_mips_precequ_ph_qbr (v4i8)
v2q15 __builtin_mips_precequ_ph_qbla (v4i8)
v2q15 __builtin_mips_precequ_ph_qbra (v4i8)
v2q15 __builtin_mips_preceu_ph_qbl (v4i8)
v2q15 __builtin_mips_preceu_ph_qbr (v4i8)
v2q15 __builtin_mips_preceu_ph_qbla (v4i8)
v2q15 __builtin_mips_preceu_ph_qbra (v4i8)
v4i8 __builtin_mips_shll_qb (v4i8, imm0_7)
v4i8 __builtin_mips_shll_qb (v4i8, i32)
v2q15 __builtin_mips_shll_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shll_ph (v2q15, i32)
v2q15 __builtin_mips_shll_s_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shll_s_ph (v2q15, i32)
q31 __builtin_mips_shll_s_w (q31, imm0_31)
q31 __builtin_mips_shll_s_w (q31, i32)
v4i8 __builtin_mips_shrl_qb (v4i8, imm0_7)
v4i8 __builtin_mips_shrl_qb (v4i8, i32)
v2q15 __builtin_mips_shra_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shra_ph (v2q15, i32)
v2q15 __builtin_mips_shra_r_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shra_r_ph (v2q15, i32)
q31 __builtin_mips_shra_r_w (q31, imm0_31)
q31 __builtin_mips_shra_r_w (q31, i32)
v2q15 __builtin_mips_muleu_s_ph_qbl (v4i8, v2q15)
v2q15 __builtin_mips_muleu_s_ph_qbr (v4i8, v2q15)
v2q15 __builtin_mips_mulq_rs_ph (v2q15, v2q15)
q31 __builtin_mips_muleq_s_w_phl (v2q15, v2q15)
q31 __builtin_mips_muleq_s_w_phr (v2q15, v2q15)
a64 __builtin_mips_dpau_h_qbl (a64, v4i8, v4i8)
a64 __builtin_mips_dpau_h_qbr (a64, v4i8, v4i8)
a64 __builtin_mips_dpsu_h_qbl (a64, v4i8, v4i8)
a64 __builtin_mips_dpsu_h_qbr (a64, v4i8, v4i8)
a64 __builtin_mips_dpaq_s_w_ph (a64, v2q15, v2q15)
a64 __builtin_mips_dpaq_sa_l_w (a64, q31, q31)
a64 __builtin_mips_dpsq_s_w_ph (a64, v2q15, v2q15)
a64 __builtin_mips_dpsq_sa_l_w (a64, q31, q31)
a64 __builtin_mips_mulsaq_s_w_ph (a64, v2q15, v2q15)
a64 __builtin_mips_maq_s_w_phl (a64, v2q15, v2q15)
a64 __builtin_mips_maq_s_w_phr (a64, v2q15, v2q15)
a64 __builtin_mips_maq_sa_w_phl (a64, v2q15, v2q15)
a64 __builtin_mips_maq_sa_w_phr (a64, v2q15, v2q15)
i32 __builtin_mips_bitrev (i32)
i32 __builtin_mips_insv (i32, i32)
v4i8 __builtin_mips_repl_qb (imm0_255)
v4i8 __builtin_mips_repl_qb (i32)
v2q15 __builtin_mips_repl_ph (imm_n512_511)
v2q15 __builtin_mips_repl_ph (i32)
void __builtin_mips_cmpu_eq_qb (v4i8, v4i8)
void __builtin_mips_cmpu_lt_qb (v4i8, v4i8)
void __builtin_mips_cmpu_le_qb (v4i8, v4i8)
i32 __builtin_mips_cmpgu_eq_qb (v4i8, v4i8)
i32 __builtin_mips_cmpgu_lt_qb (v4i8, v4i8)
i32 __builtin_mips_cmpgu_le_qb (v4i8, v4i8)
void __builtin_mips_cmp_eq_ph (v2q15, v2q15)
void __builtin_mips_cmp_lt_ph (v2q15, v2q15)
void __builtin_mips_cmp_le_ph (v2q15, v2q15)
v4i8 __builtin_mips_pick_qb (v4i8, v4i8)
v2q15 __builtin_mips_pick_ph (v2q15, v2q15)
v2q15 __builtin_mips_packrl_ph (v2q15, v2q15)
i32 __builtin_mips_extr_w (a64, imm0_31)
i32 __builtin_mips_extr_w (a64, i32)
i32 __builtin_mips_extr_r_w (a64, imm0_31)
i32 __builtin_mips_extr_s_h (a64, i32)
i32 __builtin_mips_extr_rs_w (a64, imm0_31)
i32 __builtin_mips_extr_rs_w (a64, i32)
i32 __builtin_mips_extr_s_h (a64, imm0_31)
i32 __builtin_mips_extr_r_w (a64, i32)
i32 __builtin_mips_extp (a64, imm0_31)
i32 __builtin_mips_extp (a64, i32)
i32 __builtin_mips_extpdp (a64, imm0_31)
i32 __builtin_mips_extpdp (a64, i32)
a64 __builtin_mips_shilo (a64, imm_n32_31)
a64 __builtin_mips_shilo (a64, i32)
a64 __builtin_mips_mthlip (a64, i32)
void __builtin_mips_wrdsp (i32, imm0_63)
i32 __builtin_mips_rddsp (imm0_63)
i32 __builtin_mips_lbux (void *, i32)
i32 __builtin_mips_lhx (void *, i32)
i32 __builtin_mips_lwx (void *, i32)
i32 __builtin_mips_bposge32 (void)
@end smallexample

@node MIPS Paired-Single Support
@subsection MIPS Paired-Single Support

The MIPS64 architecture includes a number of instructions that
operate on pairs of single-precision floating-point values.
Each pair is packed into a 64-bit floating-point register,
with one element being designated the ``upper half'' and
the other being designated the ``lower half''.

GCC supports paired-single operations using both the generic
vector extensions (@pxref{Vector Extensions}) and a collection of
MIPS-specific built-in functions.  Both kinds of support are
enabled by the @option{-mpaired-single} command-line option.

The vector type associated with paired-single values is usually
called @code{v2sf}.  It can be defined in C as follows:

@smallexample
typedef float v2sf __attribute__ ((vector_size (8)));
@end smallexample

@code{v2sf} values are initialized in the same way as aggregates.
For example:

@smallexample
v2sf a = @{1.5, 9.1@};
v2sf b;
float e, f;
b = (v2sf) @{e, f@};
@end smallexample

@emph{Note:} The CPU's endianness determines which value is stored in
the upper half of a register and which value is stored in the lower half.
On little-endian targets, the first value is the lower one and the second
value is the upper one.  The opposite order applies to big-endian targets.
For example, the code above will set the lower half of @code{a} to
@code{1.5} on little-endian targets and @code{9.1} on big-endian targets.

@menu
* Paired-Single Arithmetic::
* Paired-Single Built-in Functions::
* MIPS-3D Built-in Functions::
@end menu

@node Paired-Single Arithmetic
@subsubsection Paired-Single Arithmetic

The table below lists the @code{v2sf} operations for which hardware
support exists.  @code{a}, @code{b} and @code{c} are @code{v2sf}
values and @code{x} is an integral value.

@multitable @columnfractions .50 .50
@item C code @tab MIPS instruction
@item @code{a + b} @tab @code{add.ps}
@item @code{a - b} @tab @code{sub.ps}
@item @code{-a} @tab @code{neg.ps}
@item @code{a * b} @tab @code{mul.ps}
@item @code{a * b + c} @tab @code{madd.ps}
@item @code{a * b - c} @tab @code{msub.ps}
@item @code{-(a * b + c)} @tab @code{nmadd.ps}
@item @code{-(a * b - c)} @tab @code{nmsub.ps}
@item @code{x ? a : b} @tab @code{movn.ps}/@code{movz.ps}
@end multitable

Note that the multiply-accumulate instructions can be disabled
using the command-line option @code{-mno-fused-madd}.

@node Paired-Single Built-in Functions
@subsubsection Paired-Single Built-in Functions

The following paired-single functions map directly to a particular
MIPS instruction.  Please refer to the architecture specification
for details on what each instruction does.

@table @code
@item v2sf __builtin_mips_pll_ps (v2sf, v2sf)
Pair lower lower (@code{pll.ps}).

@item v2sf __builtin_mips_pul_ps (v2sf, v2sf)
Pair upper lower (@code{pul.ps}).

@item v2sf __builtin_mips_plu_ps (v2sf, v2sf)
Pair lower upper (@code{plu.ps}).

@item v2sf __builtin_mips_puu_ps (v2sf, v2sf)
Pair upper upper (@code{puu.ps}).

@item v2sf __builtin_mips_cvt_ps_s (float, float)
Convert pair to paired single (@code{cvt.ps.s}).

@item float __builtin_mips_cvt_s_pl (v2sf)
Convert pair lower to single (@code{cvt.s.pl}).

@item float __builtin_mips_cvt_s_pu (v2sf)
Convert pair upper to single (@code{cvt.s.pu}).

@item v2sf __builtin_mips_abs_ps (v2sf)
Absolute value (@code{abs.ps}).

@item v2sf __builtin_mips_alnv_ps (v2sf, v2sf, int)
Align variable (@code{alnv.ps}).

@emph{Note:} The value of the third parameter must be 0 or 4
modulo 8, otherwise the result will be unpredictable.  Please read the
instruction description for details.
@end table

The following multi-instruction functions are also available.
In each case, @var{cond} can be any of the 16 floating-point conditions:
@code{f}, @code{un}, @code{eq}, @code{ueq}, @code{olt}, @code{ult},
@code{ole}, @code{ule}, @code{sf}, @code{ngle}, @code{seq}, @code{ngl},
@code{lt}, @code{nge}, @code{le} or @code{ngt}.

@table @code
@item v2sf __builtin_mips_movt_c_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d})
@itemx v2sf __builtin_mips_movf_c_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d})
Conditional move based on floating point comparison (@code{c.@var{cond}.ps},
@code{movt.ps}/@code{movf.ps}).

The @code{movt} functions return the value @var{x} computed by:

@smallexample
c.@var{cond}.ps @var{cc},@var{a},@var{b}
mov.ps @var{x},@var{c}
movt.ps @var{x},@var{d},@var{cc}
@end smallexample

The @code{movf} functions are similar but use @code{movf.ps} instead
of @code{movt.ps}.

@item int __builtin_mips_upper_c_@var{cond}_ps (v2sf @var{a}, v2sf @var{b})
@itemx int __builtin_mips_lower_c_@var{cond}_ps (v2sf @var{a}, v2sf @var{b})
Comparison of two paired-single values (@code{c.@var{cond}.ps},
@code{bc1t}/@code{bc1f}).

These functions compare @var{a} and @var{b} using @code{c.@var{cond}.ps}
and return either the upper or lower half of the result.  For example:

@smallexample
v2sf a, b;
if (__builtin_mips_upper_c_eq_ps (a, b))
  upper_halves_are_equal ();
else
  upper_halves_are_unequal ();

if (__builtin_mips_lower_c_eq_ps (a, b))
  lower_halves_are_equal ();
else
  lower_halves_are_unequal ();
@end smallexample
@end table

@node MIPS-3D Built-in Functions
@subsubsection MIPS-3D Built-in Functions

The MIPS-3D Application-Specific Extension (ASE) includes additional
paired-single instructions that are designed to improve the performance
of 3D graphics operations.  Support for these instructions is controlled
by the @option{-mips3d} command-line option.

The functions listed below map directly to a particular MIPS-3D
instruction.  Please refer to the architecture specification for
more details on what each instruction does.

@table @code
@item v2sf __builtin_mips_addr_ps (v2sf, v2sf)
Reduction add (@code{addr.ps}).

@item v2sf __builtin_mips_mulr_ps (v2sf, v2sf)
Reduction multiply (@code{mulr.ps}).

@item v2sf __builtin_mips_cvt_pw_ps (v2sf)
Convert paired single to paired word (@code{cvt.pw.ps}).

@item v2sf __builtin_mips_cvt_ps_pw (v2sf)
Convert paired word to paired single (@code{cvt.ps.pw}).

@item float __builtin_mips_recip1_s (float)
@itemx double __builtin_mips_recip1_d (double)
@itemx v2sf __builtin_mips_recip1_ps (v2sf)
Reduced precision reciprocal (sequence step 1) (@code{recip1.@var{fmt}}).

@item float __builtin_mips_recip2_s (float, float)
@itemx double __builtin_mips_recip2_d (double, double)
@itemx v2sf __builtin_mips_recip2_ps (v2sf, v2sf)
Reduced precision reciprocal (sequence step 2) (@code{recip2.@var{fmt}}).

@item float __builtin_mips_rsqrt1_s (float)
@itemx double __builtin_mips_rsqrt1_d (double)
@itemx v2sf __builtin_mips_rsqrt1_ps (v2sf)
Reduced precision reciprocal square root (sequence step 1)
(@code{rsqrt1.@var{fmt}}).

@item float __builtin_mips_rsqrt2_s (float, float)
@itemx double __builtin_mips_rsqrt2_d (double, double)
@itemx v2sf __builtin_mips_rsqrt2_ps (v2sf, v2sf)
Reduced precision reciprocal square root (sequence step 2)
(@code{rsqrt2.@var{fmt}}).
@end table

The following multi-instruction functions are also available.
In each case, @var{cond} can be any of the 16 floating-point conditions:
@code{f}, @code{un}, @code{eq}, @code{ueq}, @code{olt}, @code{ult},
@code{ole}, @code{ule}, @code{sf}, @code{ngle}, @code{seq},
@code{ngl}, @code{lt}, @code{nge}, @code{le} or @code{ngt}.

@table @code
@item int __builtin_mips_cabs_@var{cond}_s (float @var{a}, float @var{b})
@itemx int __builtin_mips_cabs_@var{cond}_d (double @var{a}, double @var{b})
Absolute comparison of two scalar values (@code{cabs.@var{cond}.@var{fmt}},
@code{bc1t}/@code{bc1f}).

These functions compare @var{a} and @var{b} using @code{cabs.@var{cond}.s}
or @code{cabs.@var{cond}.d} and return the result as a boolean value.
For example:

@smallexample
float a, b;
if (__builtin_mips_cabs_eq_s (a, b))
  true ();
else
  false ();
@end smallexample

@item int __builtin_mips_upper_cabs_@var{cond}_ps (v2sf @var{a}, v2sf @var{b})
@itemx int __builtin_mips_lower_cabs_@var{cond}_ps (v2sf @var{a}, v2sf @var{b})
Absolute comparison of two paired-single values (@code{cabs.@var{cond}.ps},
@code{bc1t}/@code{bc1f}).

These functions compare @var{a} and @var{b} using @code{cabs.@var{cond}.ps}
and return either the upper or lower half of the result.  For example:

@smallexample
v2sf a, b;
if (__builtin_mips_upper_cabs_eq_ps (a, b))
  upper_halves_are_equal ();
else
  upper_halves_are_unequal ();

if (__builtin_mips_lower_cabs_eq_ps (a, b))
  lower_halves_are_equal ();
else
  lower_halves_are_unequal ();
@end smallexample

@item v2sf __builtin_mips_movt_cabs_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d})
@itemx v2sf __builtin_mips_movf_cabs_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d})
Conditional move based on absolute comparison (@code{cabs.@var{cond}.ps},
@code{movt.ps}/@code{movf.ps}).

The @code{movt} functions return the value @var{x} computed by:

@smallexample
cabs.@var{cond}.ps @var{cc},@var{a},@var{b}
mov.ps @var{x},@var{c}
movt.ps @var{x},@var{d},@var{cc}
@end smallexample

The @code{movf} functions are similar but use @code{movf.ps} instead
of @code{movt.ps}.

@item int __builtin_mips_any_c_@var{cond}_ps (v2sf @var{a}, v2sf @var{b})
@itemx int __builtin_mips_all_c_@var{cond}_ps (v2sf @var{a}, v2sf @var{b})
@itemx int __builtin_mips_any_cabs_@var{cond}_ps (v2sf @var{a}, v2sf @var{b})
@itemx int __builtin_mips_all_cabs_@var{cond}_ps (v2sf @var{a}, v2sf @var{b})
Comparison of two paired-single values
(@code{c.@var{cond}.ps}/@code{cabs.@var{cond}.ps},
@code{bc1any2t}/@code{bc1any2f}).

These functions compare @var{a} and @var{b} using @code{c.@var{cond}.ps}
or @code{cabs.@var{cond}.ps}.  The @code{any} forms return true if either
result is true and the @code{all} forms return true if both results are true.
For example:

@smallexample
v2sf a, b;
if (__builtin_mips_any_c_eq_ps (a, b))
  one_is_true ();
else
  both_are_false ();

if (__builtin_mips_all_c_eq_ps (a, b))
  both_are_true ();
else
  one_is_false ();
@end smallexample

@item int __builtin_mips_any_c_@var{cond}_4s (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d})
@itemx int __builtin_mips_all_c_@var{cond}_4s (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d})
@itemx int __builtin_mips_any_cabs_@var{cond}_4s (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d})
@itemx int __builtin_mips_all_cabs_@var{cond}_4s (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d})
Comparison of four paired-single values
(@code{c.@var{cond}.ps}/@code{cabs.@var{cond}.ps},
@code{bc1any4t}/@code{bc1any4f}).

These functions use @code{c.@var{cond}.ps} or @code{cabs.@var{cond}.ps}
to compare @var{a} with @var{b} and to compare @var{c} with @var{d}.
The @code{any} forms return true if any of the four results are true
and the @code{all} forms return true if all four results are true.
For example:

@smallexample
v2sf a, b, c, d;
if (__builtin_mips_any_c_eq_4s (a, b, c, d))
  some_are_true ();
else
  all_are_false ();

if (__builtin_mips_all_c_eq_4s (a, b, c, d))
  all_are_true ();
else
  some_are_false ();
@end smallexample
@end table

@node PowerPC AltiVec Built-in Functions
@subsection PowerPC AltiVec Built-in Functions

GCC provides an interface for the PowerPC family of processors to access
the AltiVec operations described in Motorola's AltiVec Programming
Interface Manual.  The interface is made available by including
@code{<altivec.h>} and using @option{-maltivec} and
@option{-mabi=altivec}.  The interface supports the following vector
types.

@smallexample
vector unsigned char
vector signed char
vector bool char

vector unsigned short
vector signed short
vector bool short
vector pixel

vector unsigned int
vector signed int
vector bool int
vector float
@end smallexample

GCC's implementation of the high-level language interface available from
C and C++ code differs from Motorola's documentation in several ways.

@itemize @bullet

@item
A vector constant is a list of constant expressions within curly braces.

@item
A vector initializer requires no cast if the vector constant is of the
same type as the variable it is initializing.

@item
If @code{signed} or @code{unsigned} is omitted, the signedness of the
vector type is the default signedness of the base type.  The default
varies depending on the operating system, so a portable program should
always specify the signedness.

@item
Compiling with @option{-maltivec} adds keywords @code{__vector},
@code{__pixel}, and @code{__bool}.  Macros @option{vector},
@code{pixel}, and @code{bool} are defined in @code{<altivec.h>} and can
be undefined.

@item
GCC allows using a @code{typedef} name as the type specifier for a
vector type.

@item
For C, overloaded functions are implemented with macros so the following
does not work:

@smallexample
  vec_add ((vector signed int)@{1, 2, 3, 4@}, foo);
@end smallexample

Since @code{vec_add} is a macro, the vector constant in the example
is treated as four separate arguments.  Wrap the entire argument in
parentheses for this to work.
@end itemize

@emph{Note:} Only the @code{<altivec.h>} interface is supported.
Internally, GCC uses built-in functions to achieve the functionality in
the aforementioned header file, but they are not supported and are
subject to change without notice.

The following interfaces are supported for the generic and specific
AltiVec operations and the AltiVec predicates.  In cases where there
is a direct mapping between generic and specific operations, only the
generic names are shown here, although the specific operations can also
be used.

Arguments that are documented as @code{const int} require literal
integral values within the range required for that operation.

@smallexample
vector signed char vec_abs (vector signed char);
vector signed short vec_abs (vector signed short);
vector signed int vec_abs (vector signed int);
vector float vec_abs (vector float);

vector signed char vec_abss (vector signed char);
vector signed short vec_abss (vector signed short);
vector signed int vec_abss (vector signed int);

vector signed char vec_add (vector bool char, vector signed char);
vector signed char vec_add (vector signed char, vector bool char);
vector signed char vec_add (vector signed char, vector signed char);
vector unsigned char vec_add (vector bool char, vector unsigned char);
vector unsigned char vec_add (vector unsigned char, vector bool char);
vector unsigned char vec_add (vector unsigned char,
                              vector unsigned char);
vector signed short vec_add (vector bool short, vector signed short);
vector signed short vec_add (vector signed short, vector bool short);
vector signed short vec_add (vector signed short, vector signed short);
vector unsigned short vec_add (vector bool short,
                               vector unsigned short);
vector unsigned short vec_add (vector unsigned short,
                               vector bool short);
vector unsigned short vec_add (vector unsigned short,
                               vector unsigned short);
vector signed int vec_add (vector bool int, vector signed int);
vector signed int vec_add (vector signed int, vector bool int);
vector signed int vec_add (vector signed int, vector signed int);
vector unsigned int vec_add (vector bool int, vector unsigned int);
vector unsigned int vec_add (vector unsigned int, vector bool int);
vector unsigned int vec_add (vector unsigned int, vector unsigned int);
vector float vec_add (vector float, vector float);

vector float vec_vaddfp (vector float, vector float);

vector signed int vec_vadduwm (vector bool int, vector signed int);
vector signed int vec_vadduwm (vector signed int, vector bool int);
vector signed int vec_vadduwm (vector signed int, vector signed int);
vector unsigned int vec_vadduwm (vector bool int, vector unsigned int);
vector unsigned int vec_vadduwm (vector unsigned int, vector bool int);
vector unsigned int vec_vadduwm (vector unsigned int,
                                 vector unsigned int);

vector signed short vec_vadduhm (vector bool short,
                                 vector signed short);
vector signed short vec_vadduhm (vector signed short,
                                 vector bool short);
vector signed short vec_vadduhm (vector signed short,
                                 vector signed short);
vector unsigned short vec_vadduhm (vector bool short,
                                   vector unsigned short);
vector unsigned short vec_vadduhm (vector unsigned short,
                                   vector bool short);
vector unsigned short vec_vadduhm (vector unsigned short,
                                   vector unsigned short);

vector signed char vec_vaddubm (vector bool char, vector signed char);
vector signed char vec_vaddubm (vector signed char, vector bool char);
vector signed char vec_vaddubm (vector signed char, vector signed char);
vector unsigned char vec_vaddubm (vector bool char,
                                  vector unsigned char);
vector unsigned char vec_vaddubm (vector unsigned char,
                                  vector bool char);
vector unsigned char vec_vaddubm (vector unsigned char,
                                  vector unsigned char);

vector unsigned int vec_addc (vector unsigned int, vector unsigned int);

vector unsigned char vec_adds (vector bool char, vector unsigned char);
vector unsigned char vec_adds (vector unsigned char, vector bool char);
vector unsigned char vec_adds (vector unsigned char,
                               vector unsigned char);
vector signed char vec_adds (vector bool char, vector signed char);
vector signed char vec_adds (vector signed char, vector bool char);
vector signed char vec_adds (vector signed char, vector signed char);
vector unsigned short vec_adds (vector bool short,
                                vector unsigned short);
vector unsigned short vec_adds (vector unsigned short,
                                vector bool short);
vector unsigned short vec_adds (vector unsigned short,
                                vector unsigned short);
vector signed short vec_adds (vector bool short, vector signed short);
vector signed short vec_adds (vector signed short, vector bool short);
vector signed short vec_adds (vector signed short, vector signed short);
vector unsigned int vec_adds (vector bool int, vector unsigned int);
vector unsigned int vec_adds (vector unsigned int, vector bool int);
vector unsigned int vec_adds (vector unsigned int, vector unsigned int);
vector signed int vec_adds (vector bool int, vector signed int);
vector signed int vec_adds (vector signed int, vector bool int);
vector signed int vec_adds (vector signed int, vector signed int);

vector signed int vec_vaddsws (vector bool int, vector signed int);
vector signed int vec_vaddsws (vector signed int, vector bool int);
vector signed int vec_vaddsws (vector signed int, vector signed int);

vector unsigned int vec_vadduws (vector bool int, vector unsigned int);
vector unsigned int vec_vadduws (vector unsigned int, vector bool int);
vector unsigned int vec_vadduws (vector unsigned int,
                                 vector unsigned int);

vector signed short vec_vaddshs (vector bool short,
                                 vector signed short);
vector signed short vec_vaddshs (vector signed short,
                                 vector bool short);
vector signed short vec_vaddshs (vector signed short,
                                 vector signed short);

vector unsigned short vec_vadduhs (vector bool short,
                                   vector unsigned short);
vector unsigned short vec_vadduhs (vector unsigned short,
                                   vector bool short);
vector unsigned short vec_vadduhs (vector unsigned short,
                                   vector unsigned short);

vector signed char vec_vaddsbs (vector bool char, vector signed char);
vector signed char vec_vaddsbs (vector signed char, vector bool char);
vector signed char vec_vaddsbs (vector signed char, vector signed char);

vector unsigned char vec_vaddubs (vector bool char,
                                  vector unsigned char);
vector unsigned char vec_vaddubs (vector unsigned char,
                                  vector bool char);
vector unsigned char vec_vaddubs (vector unsigned char,
                                  vector unsigned char);

vector float vec_and (vector float, vector float);
vector float vec_and (vector float, vector bool int);
vector float vec_and (vector bool int, vector float);
vector bool int vec_and (vector bool int, vector bool int);
vector signed int vec_and (vector bool int, vector signed int);
vector signed int vec_and (vector signed int, vector bool int);
vector signed int vec_and (vector signed int, vector signed int);
vector unsigned int vec_and (vector bool int, vector unsigned int);
vector unsigned int vec_and (vector unsigned int, vector bool int);
vector unsigned int vec_and (vector unsigned int, vector unsigned int);
vector bool short vec_and (vector bool short, vector bool short);
vector signed short vec_and (vector bool short, vector signed short);
vector signed short vec_and (vector signed short, vector bool short);
vector signed short vec_and (vector signed short, vector signed short);
vector unsigned short vec_and (vector bool short,
                               vector unsigned short);
vector unsigned short vec_and (vector unsigned short,
                               vector bool short);
vector unsigned short vec_and (vector unsigned short,
                               vector unsigned short);
vector signed char vec_and (vector bool char, vector signed char);
vector bool char vec_and (vector bool char, vector bool char);
vector signed char vec_and (vector signed char, vector bool char);
vector signed char vec_and (vector signed char, vector signed char);
vector unsigned char vec_and (vector bool char, vector unsigned char);
vector unsigned char vec_and (vector unsigned char, vector bool char);
vector unsigned char vec_and (vector unsigned char,
                              vector unsigned char);

vector float vec_andc (vector float, vector float);
vector float vec_andc (vector float, vector bool int);
vector float vec_andc (vector bool int, vector float);
vector bool int vec_andc (vector bool int, vector bool int);
vector signed int vec_andc (vector bool int, vector signed int);
vector signed int vec_andc (vector signed int, vector bool int);
vector signed int vec_andc (vector signed int, vector signed int);
vector unsigned int vec_andc (vector bool int, vector unsigned int);
vector unsigned int vec_andc (vector unsigned int, vector bool int);
vector unsigned int vec_andc (vector unsigned int, vector unsigned int);
vector bool short vec_andc (vector bool short, vector bool short);
vector signed short vec_andc (vector bool short, vector signed short);
vector signed short vec_andc (vector signed short, vector bool short);
vector signed short vec_andc (vector signed short, vector signed short);
vector unsigned short vec_andc (vector bool short,
                                vector unsigned short);
vector unsigned short vec_andc (vector unsigned short,
                                vector bool short);
vector unsigned short vec_andc (vector unsigned short,
                                vector unsigned short);
vector signed char vec_andc (vector bool char, vector signed char);
vector bool char vec_andc (vector bool char, vector bool char);
vector signed char vec_andc (vector signed char, vector bool char);
vector signed char vec_andc (vector signed char, vector signed char);
vector unsigned char vec_andc (vector bool char, vector unsigned char);
vector unsigned char vec_andc (vector unsigned char, vector bool char);
vector unsigned char vec_andc (vector unsigned char,
                               vector unsigned char);

vector unsigned char vec_avg (vector unsigned char,
                              vector unsigned char);
vector signed char vec_avg (vector signed char, vector signed char);
vector unsigned short vec_avg (vector unsigned short,
                               vector unsigned short);
vector signed short vec_avg (vector signed short, vector signed short);
vector unsigned int vec_avg (vector unsigned int, vector unsigned int);
vector signed int vec_avg (vector signed int, vector signed int);

vector signed int vec_vavgsw (vector signed int, vector signed int);

vector unsigned int vec_vavguw (vector unsigned int,
                                vector unsigned int);

vector signed short vec_vavgsh (vector signed short,
                                vector signed short);

vector unsigned short vec_vavguh (vector unsigned short,
                                  vector unsigned short);

vector signed char vec_vavgsb (vector signed char, vector signed char);

vector unsigned char vec_vavgub (vector unsigned char,
                                 vector unsigned char);

vector float vec_ceil (vector float);

vector signed int vec_cmpb (vector float, vector float);

vector bool char vec_cmpeq (vector signed char, vector signed char);
vector bool char vec_cmpeq (vector unsigned char, vector unsigned char);
vector bool short vec_cmpeq (vector signed short, vector signed short);
vector bool short vec_cmpeq (vector unsigned short,
                             vector unsigned short);
vector bool int vec_cmpeq (vector signed int, vector signed int);
vector bool int vec_cmpeq (vector unsigned int, vector unsigned int);
vector bool int vec_cmpeq (vector float, vector float);

vector bool int vec_vcmpeqfp (vector float, vector float);

vector bool int vec_vcmpequw (vector signed int, vector signed int);
vector bool int vec_vcmpequw (vector unsigned int, vector unsigned int);

vector bool short vec_vcmpequh (vector signed short,
                                vector signed short);
vector bool short vec_vcmpequh (vector unsigned short,
                                vector unsigned short);

vector bool char vec_vcmpequb (vector signed char, vector signed char);
vector bool char vec_vcmpequb (vector unsigned char,
                               vector unsigned char);

vector bool int vec_cmpge (vector float, vector float);

vector bool char vec_cmpgt (vector unsigned char, vector unsigned char);
vector bool char vec_cmpgt (vector signed char, vector signed char);
vector bool short vec_cmpgt (vector unsigned short,
                             vector unsigned short);
vector bool short vec_cmpgt (vector signed short, vector signed short);
vector bool int vec_cmpgt (vector unsigned int, vector unsigned int);
vector bool int vec_cmpgt (vector signed int, vector signed int);
vector bool int vec_cmpgt (vector float, vector float);

vector bool int vec_vcmpgtfp (vector float, vector float);

vector bool int vec_vcmpgtsw (vector signed int, vector signed int);

vector bool int vec_vcmpgtuw (vector unsigned int, vector unsigned int);

vector bool short vec_vcmpgtsh (vector signed short,
                                vector signed short);

vector bool short vec_vcmpgtuh (vector unsigned short,
                                vector unsigned short);

vector bool char vec_vcmpgtsb (vector signed char, vector signed char);

vector bool char vec_vcmpgtub (vector unsigned char,
                               vector unsigned char);

vector bool int vec_cmple (vector float, vector float);

vector bool char vec_cmplt (vector unsigned char, vector unsigned char);
vector bool char vec_cmplt (vector signed char, vector signed char);
vector bool short vec_cmplt (vector unsigned short,
                             vector unsigned short);
vector bool short vec_cmplt (vector signed short, vector signed short);
vector bool int vec_cmplt (vector unsigned int, vector unsigned int);
vector bool int vec_cmplt (vector signed int, vector signed int);
vector bool int vec_cmplt (vector float, vector float);

vector float vec_ctf (vector unsigned int, const int);
vector float vec_ctf (vector signed int, const int);

vector float vec_vcfsx (vector signed int, const int);

vector float vec_vcfux (vector unsigned int, const int);

vector signed int vec_cts (vector float, const int);

vector unsigned int vec_ctu (vector float, const int);

void vec_dss (const int);

void vec_dssall (void);

void vec_dst (const vector unsigned char *, int, const int);
void vec_dst (const vector signed char *, int, const int);
void vec_dst (const vector bool char *, int, const int);
void vec_dst (const vector unsigned short *, int, const int);
void vec_dst (const vector signed short *, int, const int);
void vec_dst (const vector bool short *, int, const int);
void vec_dst (const vector pixel *, int, const int);
void vec_dst (const vector unsigned int *, int, const int);
void vec_dst (const vector signed int *, int, const int);
void vec_dst (const vector bool int *, int, const int);
void vec_dst (const vector float *, int, const int);
void vec_dst (const unsigned char *, int, const int);
void vec_dst (const signed char *, int, const int);
void vec_dst (const unsigned short *, int, const int);
void vec_dst (const short *, int, const int);
void vec_dst (const unsigned int *, int, const int);
void vec_dst (const int *, int, const int);
void vec_dst (const unsigned long *, int, const int);
void vec_dst (const long *, int, const int);
void vec_dst (const float *, int, const int);

void vec_dstst (const vector unsigned char *, int, const int);
void vec_dstst (const vector signed char *, int, const int);
void vec_dstst (const vector bool char *, int, const int);
void vec_dstst (const vector unsigned short *, int, const int);
void vec_dstst (const vector signed short *, int, const int);
void vec_dstst (const vector bool short *, int, const int);
void vec_dstst (const vector pixel *, int, const int);
void vec_dstst (const vector unsigned int *, int, const int);
void vec_dstst (const vector signed int *, int, const int);
void vec_dstst (const vector bool int *, int, const int);
void vec_dstst (const vector float *, int, const int);
void vec_dstst (const unsigned char *, int, const int);
void vec_dstst (const signed char *, int, const int);
void vec_dstst (const unsigned short *, int, const int);
void vec_dstst (const short *, int, const int);
void vec_dstst (const unsigned int *, int, const int);
void vec_dstst (const int *, int, const int);
void vec_dstst (const unsigned long *, int, const int);
void vec_dstst (const long *, int, const int);
void vec_dstst (const float *, int, const int);

void vec_dststt (const vector unsigned char *, int, const int);
void vec_dststt (const vector signed char *, int, const int);
void vec_dststt (const vector bool char *, int, const int);
void vec_dststt (const vector unsigned short *, int, const int);
void vec_dststt (const vector signed short *, int, const int);
void vec_dststt (const vector bool short *, int, const int);
void vec_dststt (const vector pixel *, int, const int);
void vec_dststt (const vector unsigned int *, int, const int);
void vec_dststt (const vector signed int *, int, const int);
void vec_dststt (const vector bool int *, int, const int);
void vec_dststt (const vector float *, int, const int);
void vec_dststt (const unsigned char *, int, const int);
void vec_dststt (const signed char *, int, const int);
void vec_dststt (const unsigned short *, int, const int);
void vec_dststt (const short *, int, const int);
void vec_dststt (const unsigned int *, int, const int);
void vec_dststt (const int *, int, const int);
void vec_dststt (const unsigned long *, int, const int);
void vec_dststt (const long *, int, const int);
void vec_dststt (const float *, int, const int);

void vec_dstt (const vector unsigned char *, int, const int);
void vec_dstt (const vector signed char *, int, const int);
void vec_dstt (const vector bool char *, int, const int);
void vec_dstt (const vector unsigned short *, int, const int);
void vec_dstt (const vector signed short *, int, const int);
void vec_dstt (const vector bool short *, int, const int);
void vec_dstt (const vector pixel *, int, const int);
void vec_dstt (const vector unsigned int *, int, const int);
void vec_dstt (const vector signed int *, int, const int);
void vec_dstt (const vector bool int *, int, const int);
void vec_dstt (const vector float *, int, const int);
void vec_dstt (const unsigned char *, int, const int);
void vec_dstt (const signed char *, int, const int);
void vec_dstt (const unsigned short *, int, const int);
void vec_dstt (const short *, int, const int);
void vec_dstt (const unsigned int *, int, const int);
void vec_dstt (const int *, int, const int);
void vec_dstt (const unsigned long *, int, const int);
void vec_dstt (const long *, int, const int);
void vec_dstt (const float *, int, const int);

vector float vec_expte (vector float);

vector float vec_floor (vector float);

vector float vec_ld (int, const vector float *);
vector float vec_ld (int, const float *);
vector bool int vec_ld (int, const vector bool int *);
vector signed int vec_ld (int, const vector signed int *);
vector signed int vec_ld (int, const int *);
vector signed int vec_ld (int, const long *);
vector unsigned int vec_ld (int, const vector unsigned int *);
vector unsigned int vec_ld (int, const unsigned int *);
vector unsigned int vec_ld (int, const unsigned long *);
vector bool short vec_ld (int, const vector bool short *);
vector pixel vec_ld (int, const vector pixel *);
vector signed short vec_ld (int, const vector signed short *);
vector signed short vec_ld (int, const short *);
vector unsigned short vec_ld (int, const vector unsigned short *);
vector unsigned short vec_ld (int, const unsigned short *);
vector bool char vec_ld (int, const vector bool char *);
vector signed char vec_ld (int, const vector signed char *);
vector signed char vec_ld (int, const signed char *);
vector unsigned char vec_ld (int, const vector unsigned char *);
vector unsigned char vec_ld (int, const unsigned char *);

vector signed char vec_lde (int, const signed char *);
vector unsigned char vec_lde (int, const unsigned char *);
vector signed short vec_lde (int, const short *);
vector unsigned short vec_lde (int, const unsigned short *);
vector float vec_lde (int, const float *);
vector signed int vec_lde (int, const int *);
vector unsigned int vec_lde (int, const unsigned int *);
vector signed int vec_lde (int, const long *);
vector unsigned int vec_lde (int, const unsigned long *);

vector float vec_lvewx (int, float *);
vector signed int vec_lvewx (int, int *);
vector unsigned int vec_lvewx (int, unsigned int *);
vector signed int vec_lvewx (int, long *);
vector unsigned int vec_lvewx (int, unsigned long *);

vector signed short vec_lvehx (int, short *);
vector unsigned short vec_lvehx (int, unsigned short *);

vector signed char vec_lvebx (int, char *);
vector unsigned char vec_lvebx (int, unsigned char *);

vector float vec_ldl (int, const vector float *);
vector float vec_ldl (int, const float *);
vector bool int vec_ldl (int, const vector bool int *);
vector signed int vec_ldl (int, const vector signed int *);
vector signed int vec_ldl (int, const int *);
vector signed int vec_ldl (int, const long *);
vector unsigned int vec_ldl (int, const vector unsigned int *);
vector unsigned int vec_ldl (int, const unsigned int *);
vector unsigned int vec_ldl (int, const unsigned long *);
vector bool short vec_ldl (int, const vector bool short *);
vector pixel vec_ldl (int, const vector pixel *);
vector signed short vec_ldl (int, const vector signed short *);
vector signed short vec_ldl (int, const short *);
vector unsigned short vec_ldl (int, const vector unsigned short *);
vector unsigned short vec_ldl (int, const unsigned short *);
vector bool char vec_ldl (int, const vector bool char *);
vector signed char vec_ldl (int, const vector signed char *);
vector signed char vec_ldl (int, const signed char *);
vector unsigned char vec_ldl (int, const vector unsigned char *);
vector unsigned char vec_ldl (int, const unsigned char *);

vector float vec_loge (vector float);

vector unsigned char vec_lvsl (int, const volatile unsigned char *);
vector unsigned char vec_lvsl (int, const volatile signed char *);
vector unsigned char vec_lvsl (int, const volatile unsigned short *);
vector unsigned char vec_lvsl (int, const volatile short *);
vector unsigned char vec_lvsl (int, const volatile unsigned int *);
vector unsigned char vec_lvsl (int, const volatile int *);
vector unsigned char vec_lvsl (int, const volatile unsigned long *);
vector unsigned char vec_lvsl (int, const volatile long *);
vector unsigned char vec_lvsl (int, const volatile float *);

vector unsigned char vec_lvsr (int, const volatile unsigned char *);
vector unsigned char vec_lvsr (int, const volatile signed char *);
vector unsigned char vec_lvsr (int, const volatile unsigned short *);
vector unsigned char vec_lvsr (int, const volatile short *);
vector unsigned char vec_lvsr (int, const volatile unsigned int *);
vector unsigned char vec_lvsr (int, const volatile int *);
vector unsigned char vec_lvsr (int, const volatile unsigned long *);
vector unsigned char vec_lvsr (int, const volatile long *);
vector unsigned char vec_lvsr (int, const volatile float *);

vector float vec_madd (vector float, vector float, vector float);

vector signed short vec_madds (vector signed short,
                               vector signed short,
                               vector signed short);

vector unsigned char vec_max (vector bool char, vector unsigned char);
vector unsigned char vec_max (vector unsigned char, vector bool char);
vector unsigned char vec_max (vector unsigned char,
                              vector unsigned char);
vector signed char vec_max (vector bool char, vector signed char);
vector signed char vec_max (vector signed char, vector bool char);
vector signed char vec_max (vector signed char, vector signed char);
vector unsigned short vec_max (vector bool short,
                               vector unsigned short);
vector unsigned short vec_max (vector unsigned short,
                               vector bool short);
vector unsigned short vec_max (vector unsigned short,
                               vector unsigned short);
vector signed short vec_max (vector bool short, vector signed short);
vector signed short vec_max (vector signed short, vector bool short);
vector signed short vec_max (vector signed short, vector signed short);
vector unsigned int vec_max (vector bool int, vector unsigned int);
vector unsigned int vec_max (vector unsigned int, vector bool int);
vector unsigned int vec_max (vector unsigned int, vector unsigned int);
vector signed int vec_max (vector bool int, vector signed int);
vector signed int vec_max (vector signed int, vector bool int);
vector signed int vec_max (vector signed int, vector signed int);
vector float vec_max (vector float, vector float);

vector float vec_vmaxfp (vector float, vector float);

vector signed int vec_vmaxsw (vector bool int, vector signed int);
vector signed int vec_vmaxsw (vector signed int, vector bool int);
vector signed int vec_vmaxsw (vector signed int, vector signed int);

vector unsigned int vec_vmaxuw (vector bool int, vector unsigned int);
vector unsigned int vec_vmaxuw (vector unsigned int, vector bool int);
vector unsigned int vec_vmaxuw (vector unsigned int,
                                vector unsigned int);

vector signed short vec_vmaxsh (vector bool short, vector signed short);
vector signed short vec_vmaxsh (vector signed short, vector bool short);
vector signed short vec_vmaxsh (vector signed short,
                                vector signed short);

vector unsigned short vec_vmaxuh (vector bool short,
                                  vector unsigned short);
vector unsigned short vec_vmaxuh (vector unsigned short,
                                  vector bool short);
vector unsigned short vec_vmaxuh (vector unsigned short,
                                  vector unsigned short);

vector signed char vec_vmaxsb (vector bool char, vector signed char);
vector signed char vec_vmaxsb (vector signed char, vector bool char);
vector signed char vec_vmaxsb (vector signed char, vector signed char);

vector unsigned char vec_vmaxub (vector bool char,
                                 vector unsigned char);
vector unsigned char vec_vmaxub (vector unsigned char,
                                 vector bool char);
vector unsigned char vec_vmaxub (vector unsigned char,
                                 vector unsigned char);

vector bool char vec_mergeh (vector bool char, vector bool char);
vector signed char vec_mergeh (vector signed char, vector signed char);
vector unsigned char vec_mergeh (vector unsigned char,
                                 vector unsigned char);
vector bool short vec_mergeh (vector bool short, vector bool short);
vector pixel vec_mergeh (vector pixel, vector pixel);
vector signed short vec_mergeh (vector signed short,
                                vector signed short);
vector unsigned short vec_mergeh (vector unsigned short,
                                  vector unsigned short);
vector float vec_mergeh (vector float, vector float);
vector bool int vec_mergeh (vector bool int, vector bool int);
vector signed int vec_mergeh (vector signed int, vector signed int);
vector unsigned int vec_mergeh (vector unsigned int,
                                vector unsigned int);

vector float vec_vmrghw (vector float, vector float);
vector bool int vec_vmrghw (vector bool int, vector bool int);
vector signed int vec_vmrghw (vector signed int, vector signed int);
vector unsigned int vec_vmrghw (vector unsigned int,
                                vector unsigned int);

vector bool short vec_vmrghh (vector bool short, vector bool short);
vector signed short vec_vmrghh (vector signed short,
                                vector signed short);
vector unsigned short vec_vmrghh (vector unsigned short,
                                  vector unsigned short);
vector pixel vec_vmrghh (vector pixel, vector pixel);

vector bool char vec_vmrghb (vector bool char, vector bool char);
vector signed char vec_vmrghb (vector signed char, vector signed char);
vector unsigned char vec_vmrghb (vector unsigned char,
                                 vector unsigned char);

vector bool char vec_mergel (vector bool char, vector bool char);
vector signed char vec_mergel (vector signed char, vector signed char);
vector unsigned char vec_mergel (vector unsigned char,
                                 vector unsigned char);
vector bool short vec_mergel (vector bool short, vector bool short);
vector pixel vec_mergel (vector pixel, vector pixel);
vector signed short vec_mergel (vector signed short,
                                vector signed short);
vector unsigned short vec_mergel (vector unsigned short,
                                  vector unsigned short);
vector float vec_mergel (vector float, vector float);
vector bool int vec_mergel (vector bool int, vector bool int);
vector signed int vec_mergel (vector signed int, vector signed int);
vector unsigned int vec_mergel (vector unsigned int,
                                vector unsigned int);

vector float vec_vmrglw (vector float, vector float);
vector signed int vec_vmrglw (vector signed int, vector signed int);
vector unsigned int vec_vmrglw (vector unsigned int,
                                vector unsigned int);
vector bool int vec_vmrglw (vector bool int, vector bool int);

vector bool short vec_vmrglh (vector bool short, vector bool short);
vector signed short vec_vmrglh (vector signed short,
                                vector signed short);
vector unsigned short vec_vmrglh (vector unsigned short,
                                  vector unsigned short);
vector pixel vec_vmrglh (vector pixel, vector pixel);

vector bool char vec_vmrglb (vector bool char, vector bool char);
vector signed char vec_vmrglb (vector signed char, vector signed char);
vector unsigned char vec_vmrglb (vector unsigned char,
                                 vector unsigned char);

vector unsigned short vec_mfvscr (void);

vector unsigned char vec_min (vector bool char, vector unsigned char);
vector unsigned char vec_min (vector unsigned char, vector bool char);
vector unsigned char vec_min (vector unsigned char,
                              vector unsigned char);
vector signed char vec_min (vector bool char, vector signed char);
vector signed char vec_min (vector signed char, vector bool char);
vector signed char vec_min (vector signed char, vector signed char);
vector unsigned short vec_min (vector bool short,
                               vector unsigned short);
vector unsigned short vec_min (vector unsigned short,
                               vector bool short);
vector unsigned short vec_min (vector unsigned short,
                               vector unsigned short);
vector signed short vec_min (vector bool short, vector signed short);
vector signed short vec_min (vector signed short, vector bool short);
vector signed short vec_min (vector signed short, vector signed short);
vector unsigned int vec_min (vector bool int, vector unsigned int);
vector unsigned int vec_min (vector unsigned int, vector bool int);
vector unsigned int vec_min (vector unsigned int, vector unsigned int);
vector signed int vec_min (vector bool int, vector signed int);
vector signed int vec_min (vector signed int, vector bool int);
vector signed int vec_min (vector signed int, vector signed int);
vector float vec_min (vector float, vector float);

vector float vec_vminfp (vector float, vector float);

vector signed int vec_vminsw (vector bool int, vector signed int);
vector signed int vec_vminsw (vector signed int, vector bool int);
vector signed int vec_vminsw (vector signed int, vector signed int);

vector unsigned int vec_vminuw (vector bool int, vector unsigned int);
vector unsigned int vec_vminuw (vector unsigned int, vector bool int);
vector unsigned int vec_vminuw (vector unsigned int,
                                vector unsigned int);

vector signed short vec_vminsh (vector bool short, vector signed short);
vector signed short vec_vminsh (vector signed short, vector bool short);
vector signed short vec_vminsh (vector signed short,
                                vector signed short);

vector unsigned short vec_vminuh (vector bool short,
                                  vector unsigned short);
vector unsigned short vec_vminuh (vector unsigned short,
                                  vector bool short);
vector unsigned short vec_vminuh (vector unsigned short,
                                  vector unsigned short);

vector signed char vec_vminsb (vector bool char, vector signed char);
vector signed char vec_vminsb (vector signed char, vector bool char);
vector signed char vec_vminsb (vector signed char, vector signed char);

vector unsigned char vec_vminub (vector bool char,
                                 vector unsigned char);
vector unsigned char vec_vminub (vector unsigned char,
                                 vector bool char);
vector unsigned char vec_vminub (vector unsigned char,
                                 vector unsigned char);

vector signed short vec_mladd (vector signed short,
                               vector signed short,
                               vector signed short);
vector signed short vec_mladd (vector signed short,
                               vector unsigned short,
                               vector unsigned short);
vector signed short vec_mladd (vector unsigned short,
                               vector signed short,
                               vector signed short);
vector unsigned short vec_mladd (vector unsigned short,
                                 vector unsigned short,
                                 vector unsigned short);

vector signed short vec_mradds (vector signed short,
                                vector signed short,
                                vector signed short);

vector unsigned int vec_msum (vector unsigned char,
                              vector unsigned char,
                              vector unsigned int);
vector signed int vec_msum (vector signed char,
                            vector unsigned char,
                            vector signed int);
vector unsigned int vec_msum (vector unsigned short,
                              vector unsigned short,
                              vector unsigned int);
vector signed int vec_msum (vector signed short,
                            vector signed short,
                            vector signed int);

vector signed int vec_vmsumshm (vector signed short,
                                vector signed short,
                                vector signed int);

vector unsigned int vec_vmsumuhm (vector unsigned short,
                                  vector unsigned short,
                                  vector unsigned int);

vector signed int vec_vmsummbm (vector signed char,
                                vector unsigned char,
                                vector signed int);

vector unsigned int vec_vmsumubm (vector unsigned char,
                                  vector unsigned char,
                                  vector unsigned int);

vector unsigned int vec_msums (vector unsigned short,
                               vector unsigned short,
                               vector unsigned int);
vector signed int vec_msums (vector signed short,
                             vector signed short,
                             vector signed int);

vector signed int vec_vmsumshs (vector signed short,
                                vector signed short,
                                vector signed int);

vector unsigned int vec_vmsumuhs (vector unsigned short,
                                  vector unsigned short,
                                  vector unsigned int);

void vec_mtvscr (vector signed int);
void vec_mtvscr (vector unsigned int);
void vec_mtvscr (vector bool int);
void vec_mtvscr (vector signed short);
void vec_mtvscr (vector unsigned short);
void vec_mtvscr (vector bool short);
void vec_mtvscr (vector pixel);
void vec_mtvscr (vector signed char);
void vec_mtvscr (vector unsigned char);
void vec_mtvscr (vector bool char);

vector unsigned short vec_mule (vector unsigned char,
                                vector unsigned char);
vector signed short vec_mule (vector signed char,
                              vector signed char);
vector unsigned int vec_mule (vector unsigned short,
                              vector unsigned short);
vector signed int vec_mule (vector signed short, vector signed short);

vector signed int vec_vmulesh (vector signed short,
                               vector signed short);

vector unsigned int vec_vmuleuh (vector unsigned short,
                                 vector unsigned short);

vector signed short vec_vmulesb (vector signed char,
                                 vector signed char);

vector unsigned short vec_vmuleub (vector unsigned char,
                                  vector unsigned char);

vector unsigned short vec_mulo (vector unsigned char,
                                vector unsigned char);
vector signed short vec_mulo (vector signed char, vector signed char);
vector unsigned int vec_mulo (vector unsigned short,
                              vector unsigned short);
vector signed int vec_mulo (vector signed short, vector signed short);

vector signed int vec_vmulosh (vector signed short,
                               vector signed short);

vector unsigned int vec_vmulouh (vector unsigned short,
                                 vector unsigned short);

vector signed short vec_vmulosb (vector signed char,
                                 vector signed char);

vector unsigned short vec_vmuloub (vector unsigned char,
                                   vector unsigned char);

vector float vec_nmsub (vector float, vector float, vector float);

vector float vec_nor (vector float, vector float);
vector signed int vec_nor (vector signed int, vector signed int);
vector unsigned int vec_nor (vector unsigned int, vector unsigned int);
vector bool int vec_nor (vector bool int, vector bool int);
vector signed short vec_nor (vector signed short, vector signed short);
vector unsigned short vec_nor (vector unsigned short,
                               vector unsigned short);
vector bool short vec_nor (vector bool short, vector bool short);
vector signed char vec_nor (vector signed char, vector signed char);
vector unsigned char vec_nor (vector unsigned char,
                              vector unsigned char);
vector bool char vec_nor (vector bool char, vector bool char);

vector float vec_or (vector float, vector float);
vector float vec_or (vector float, vector bool int);
vector float vec_or (vector bool int, vector float);
vector bool int vec_or (vector bool int, vector bool int);
vector signed int vec_or (vector bool int, vector signed int);
vector signed int vec_or (vector signed int, vector bool int);
vector signed int vec_or (vector signed int, vector signed int);
vector unsigned int vec_or (vector bool int, vector unsigned int);
vector unsigned int vec_or (vector unsigned int, vector bool int);
vector unsigned int vec_or (vector unsigned int, vector unsigned int);
vector bool short vec_or (vector bool short, vector bool short);
vector signed short vec_or (vector bool short, vector signed short);
vector signed short vec_or (vector signed short, vector bool short);
vector signed short vec_or (vector signed short, vector signed short);
vector unsigned short vec_or (vector bool short, vector unsigned short);
vector unsigned short vec_or (vector unsigned short, vector bool short);
vector unsigned short vec_or (vector unsigned short,
                              vector unsigned short);
vector signed char vec_or (vector bool char, vector signed char);
vector bool char vec_or (vector bool char, vector bool char);
vector signed char vec_or (vector signed char, vector bool char);
vector signed char vec_or (vector signed char, vector signed char);
vector unsigned char vec_or (vector bool char, vector unsigned char);
vector unsigned char vec_or (vector unsigned char, vector bool char);
vector unsigned char vec_or (vector unsigned char,
                             vector unsigned char);

vector signed char vec_pack (vector signed short, vector signed short);
vector unsigned char vec_pack (vector unsigned short,
                               vector unsigned short);
vector bool char vec_pack (vector bool short, vector bool short);
vector signed short vec_pack (vector signed int, vector signed int);
vector unsigned short vec_pack (vector unsigned int,
                                vector unsigned int);
vector bool short vec_pack (vector bool int, vector bool int);

vector bool short vec_vpkuwum (vector bool int, vector bool int);
vector signed short vec_vpkuwum (vector signed int, vector signed int);
vector unsigned short vec_vpkuwum (vector unsigned int,
                                   vector unsigned int);

vector bool char vec_vpkuhum (vector bool short, vector bool short);
vector signed char vec_vpkuhum (vector signed short,
                                vector signed short);
vector unsigned char vec_vpkuhum (vector unsigned short,
                                  vector unsigned short);

vector pixel vec_packpx (vector unsigned int, vector unsigned int);

vector unsigned char vec_packs (vector unsigned short,
                                vector unsigned short);
vector signed char vec_packs (vector signed short, vector signed short);
vector unsigned short vec_packs (vector unsigned int,
                                 vector unsigned int);
vector signed short vec_packs (vector signed int, vector signed int);

vector signed short vec_vpkswss (vector signed int, vector signed int);

vector unsigned short vec_vpkuwus (vector unsigned int,
                                   vector unsigned int);

vector signed char vec_vpkshss (vector signed short,
                                vector signed short);

vector unsigned char vec_vpkuhus (vector unsigned short,
                                  vector unsigned short);

vector unsigned char vec_packsu (vector unsigned short,
                                 vector unsigned short);
vector unsigned char vec_packsu (vector signed short,
                                 vector signed short);
vector unsigned short vec_packsu (vector unsigned int,
                                  vector unsigned int);
vector unsigned short vec_packsu (vector signed int, vector signed int);

vector unsigned short vec_vpkswus (vector signed int,
                                   vector signed int);

vector unsigned char vec_vpkshus (vector signed short,
                                  vector signed short);

vector float vec_perm (vector float,
                       vector float,
                       vector unsigned char);
vector signed int vec_perm (vector signed int,
                            vector signed int,
                            vector unsigned char);
vector unsigned int vec_perm (vector unsigned int,
                              vector unsigned int,
                              vector unsigned char);
vector bool int vec_perm (vector bool int,
                          vector bool int,
                          vector unsigned char);
vector signed short vec_perm (vector signed short,
                              vector signed short,
                              vector unsigned char);
vector unsigned short vec_perm (vector unsigned short,
                                vector unsigned short,
                                vector unsigned char);
vector bool short vec_perm (vector bool short,
                            vector bool short,
                            vector unsigned char);
vector pixel vec_perm (vector pixel,
                       vector pixel,
                       vector unsigned char);
vector signed char vec_perm (vector signed char,
                             vector signed char,
                             vector unsigned char);
vector unsigned char vec_perm (vector unsigned char,
                               vector unsigned char,
                               vector unsigned char);
vector bool char vec_perm (vector bool char,
                           vector bool char,
                           vector unsigned char);

vector float vec_re (vector float);

vector signed char vec_rl (vector signed char,
                           vector unsigned char);
vector unsigned char vec_rl (vector unsigned char,
                             vector unsigned char);
vector signed short vec_rl (vector signed short, vector unsigned short);
vector unsigned short vec_rl (vector unsigned short,
                              vector unsigned short);
vector signed int vec_rl (vector signed int, vector unsigned int);
vector unsigned int vec_rl (vector unsigned int, vector unsigned int);

vector signed int vec_vrlw (vector signed int, vector unsigned int);
vector unsigned int vec_vrlw (vector unsigned int, vector unsigned int);

vector signed short vec_vrlh (vector signed short,
                              vector unsigned short);
vector unsigned short vec_vrlh (vector unsigned short,
                                vector unsigned short);

vector signed char vec_vrlb (vector signed char, vector unsigned char);
vector unsigned char vec_vrlb (vector unsigned char,
                               vector unsigned char);

vector float vec_round (vector float);

vector float vec_rsqrte (vector float);

vector float vec_sel (vector float, vector float, vector bool int);
vector float vec_sel (vector float, vector float, vector unsigned int);
vector signed int vec_sel (vector signed int,
                           vector signed int,
                           vector bool int);
vector signed int vec_sel (vector signed int,
                           vector signed int,
                           vector unsigned int);
vector unsigned int vec_sel (vector unsigned int,
                             vector unsigned int,
                             vector bool int);
vector unsigned int vec_sel (vector unsigned int,
                             vector unsigned int,
                             vector unsigned int);
vector bool int vec_sel (vector bool int,
                         vector bool int,
                         vector bool int);
vector bool int vec_sel (vector bool int,
                         vector bool int,
                         vector unsigned int);
vector signed short vec_sel (vector signed short,
                             vector signed short,
                             vector bool short);
vector signed short vec_sel (vector signed short,
                             vector signed short,
                             vector unsigned short);
vector unsigned short vec_sel (vector unsigned short,
                               vector unsigned short,
                               vector bool short);
vector unsigned short vec_sel (vector unsigned short,
                               vector unsigned short,
                               vector unsigned short);
vector bool short vec_sel (vector bool short,
                           vector bool short,
                           vector bool short);
vector bool short vec_sel (vector bool short,
                           vector bool short,
                           vector unsigned short);
vector signed char vec_sel (vector signed char,
                            vector signed char,
                            vector bool char);
vector signed char vec_sel (vector signed char,
                            vector signed char,
                            vector unsigned char);
vector unsigned char vec_sel (vector unsigned char,
                              vector unsigned char,
                              vector bool char);
vector unsigned char vec_sel (vector unsigned char,
                              vector unsigned char,
                              vector unsigned char);
vector bool char vec_sel (vector bool char,
                          vector bool char,
                          vector bool char);
vector bool char vec_sel (vector bool char,
                          vector bool char,
                          vector unsigned char);

vector signed char vec_sl (vector signed char,
                           vector unsigned char);
vector unsigned char vec_sl (vector unsigned char,
                             vector unsigned char);
vector signed short vec_sl (vector signed short, vector unsigned short);
vector unsigned short vec_sl (vector unsigned short,
                              vector unsigned short);
vector signed int vec_sl (vector signed int, vector unsigned int);
vector unsigned int vec_sl (vector unsigned int, vector unsigned int);

vector signed int vec_vslw (vector signed int, vector unsigned int);
vector unsigned int vec_vslw (vector unsigned int, vector unsigned int);

vector signed short vec_vslh (vector signed short,
                              vector unsigned short);
vector unsigned short vec_vslh (vector unsigned short,
                                vector unsigned short);

vector signed char vec_vslb (vector signed char, vector unsigned char);
vector unsigned char vec_vslb (vector unsigned char,
                               vector unsigned char);

vector float vec_sld (vector float, vector float, const int);
vector signed int vec_sld (vector signed int,
                           vector signed int,
                           const int);
vector unsigned int vec_sld (vector unsigned int,
                             vector unsigned int,
                             const int);
vector bool int vec_sld (vector bool int,
                         vector bool int,
                         const int);
vector signed short vec_sld (vector signed short,
                             vector signed short,
                             const int);
vector unsigned short vec_sld (vector unsigned short,
                               vector unsigned short,
                               const int);
vector bool short vec_sld (vector bool short,
                           vector bool short,
                           const int);
vector pixel vec_sld (vector pixel,
                      vector pixel,
                      const int);
vector signed char vec_sld (vector signed char,
                            vector signed char,
                            const int);
vector unsigned char vec_sld (vector unsigned char,
                              vector unsigned char,
                              const int);
vector bool char vec_sld (vector bool char,
                          vector bool char,
                          const int);

vector signed int vec_sll (vector signed int,
                           vector unsigned int);
vector signed int vec_sll (vector signed int,
                           vector unsigned short);
vector signed int vec_sll (vector signed int,
                           vector unsigned char);
vector unsigned int vec_sll (vector unsigned int,
                             vector unsigned int);
vector unsigned int vec_sll (vector unsigned int,
                             vector unsigned short);
vector unsigned int vec_sll (vector unsigned int,
                             vector unsigned char);
vector bool int vec_sll (vector bool int,
                         vector unsigned int);
vector bool int vec_sll (vector bool int,
                         vector unsigned short);
vector bool int vec_sll (vector bool int,
                         vector unsigned char);
vector signed short vec_sll (vector signed short,
                             vector unsigned int);
vector signed short vec_sll (vector signed short,
                             vector unsigned short);
vector signed short vec_sll (vector signed short,
                             vector unsigned char);
vector unsigned short vec_sll (vector unsigned short,
                               vector unsigned int);
vector unsigned short vec_sll (vector unsigned short,
                               vector unsigned short);
vector unsigned short vec_sll (vector unsigned short,
                               vector unsigned char);
vector bool short vec_sll (vector bool short, vector unsigned int);
vector bool short vec_sll (vector bool short, vector unsigned short);
vector bool short vec_sll (vector bool short, vector unsigned char);
vector pixel vec_sll (vector pixel, vector unsigned int);
vector pixel vec_sll (vector pixel, vector unsigned short);
vector pixel vec_sll (vector pixel, vector unsigned char);
vector signed char vec_sll (vector signed char, vector unsigned int);
vector signed char vec_sll (vector signed char, vector unsigned short);
vector signed char vec_sll (vector signed char, vector unsigned char);
vector unsigned char vec_sll (vector unsigned char,
                              vector unsigned int);
vector unsigned char vec_sll (vector unsigned char,
                              vector unsigned short);
vector unsigned char vec_sll (vector unsigned char,
                              vector unsigned char);
vector bool char vec_sll (vector bool char, vector unsigned int);
vector bool char vec_sll (vector bool char, vector unsigned short);
vector bool char vec_sll (vector bool char, vector unsigned char);

vector float vec_slo (vector float, vector signed char);
vector float vec_slo (vector float, vector unsigned char);
vector signed int vec_slo (vector signed int, vector signed char);
vector signed int vec_slo (vector signed int, vector unsigned char);
vector unsigned int vec_slo (vector unsigned int, vector signed char);
vector unsigned int vec_slo (vector unsigned int, vector unsigned char);
vector signed short vec_slo (vector signed short, vector signed char);
vector signed short vec_slo (vector signed short, vector unsigned char);
vector unsigned short vec_slo (vector unsigned short,
                               vector signed char);
vector unsigned short vec_slo (vector unsigned short,
                               vector unsigned char);
vector pixel vec_slo (vector pixel, vector signed char);
vector pixel vec_slo (vector pixel, vector unsigned char);
vector signed char vec_slo (vector signed char, vector signed char);
vector signed char vec_slo (vector signed char, vector unsigned char);
vector unsigned char vec_slo (vector unsigned char, vector signed char);
vector unsigned char vec_slo (vector unsigned char,
                              vector unsigned char);

vector signed char vec_splat (vector signed char, const int);
vector unsigned char vec_splat (vector unsigned char, const int);
vector bool char vec_splat (vector bool char, const int);
vector signed short vec_splat (vector signed short, const int);
vector unsigned short vec_splat (vector unsigned short, const int);
vector bool short vec_splat (vector bool short, const int);
vector pixel vec_splat (vector pixel, const int);
vector float vec_splat (vector float, const int);
vector signed int vec_splat (vector signed int, const int);
vector unsigned int vec_splat (vector unsigned int, const int);
vector bool int vec_splat (vector bool int, const int);

vector float vec_vspltw (vector float, const int);
vector signed int vec_vspltw (vector signed int, const int);
vector unsigned int vec_vspltw (vector unsigned int, const int);
vector bool int vec_vspltw (vector bool int, const int);

vector bool short vec_vsplth (vector bool short, const int);
vector signed short vec_vsplth (vector signed short, const int);
vector unsigned short vec_vsplth (vector unsigned short, const int);
vector pixel vec_vsplth (vector pixel, const int);

vector signed char vec_vspltb (vector signed char, const int);
vector unsigned char vec_vspltb (vector unsigned char, const int);
vector bool char vec_vspltb (vector bool char, const int);

vector signed char vec_splat_s8 (const int);

vector signed short vec_splat_s16 (const int);

vector signed int vec_splat_s32 (const int);

vector unsigned char vec_splat_u8 (const int);

vector unsigned short vec_splat_u16 (const int);

vector unsigned int vec_splat_u32 (const int);

vector signed char vec_sr (vector signed char, vector unsigned char);
vector unsigned char vec_sr (vector unsigned char,
                             vector unsigned char);
vector signed short vec_sr (vector signed short,
                            vector unsigned short);
vector unsigned short vec_sr (vector unsigned short,
                              vector unsigned short);
vector signed int vec_sr (vector signed int, vector unsigned int);
vector unsigned int vec_sr (vector unsigned int, vector unsigned int);

vector signed int vec_vsrw (vector signed int, vector unsigned int);
vector unsigned int vec_vsrw (vector unsigned int, vector unsigned int);

vector signed short vec_vsrh (vector signed short,
                              vector unsigned short);
vector unsigned short vec_vsrh (vector unsigned short,
                                vector unsigned short);

vector signed char vec_vsrb (vector signed char, vector unsigned char);
vector unsigned char vec_vsrb (vector unsigned char,
                               vector unsigned char);

vector signed char vec_sra (vector signed char, vector unsigned char);
vector unsigned char vec_sra (vector unsigned char,
                              vector unsigned char);
vector signed short vec_sra (vector signed short,
                             vector unsigned short);
vector unsigned short vec_sra (vector unsigned short,
                               vector unsigned short);
vector signed int vec_sra (vector signed int, vector unsigned int);
vector unsigned int vec_sra (vector unsigned int, vector unsigned int);

vector signed int vec_vsraw (vector signed int, vector unsigned int);
vector unsigned int vec_vsraw (vector unsigned int,
                               vector unsigned int);

vector signed short vec_vsrah (vector signed short,
                               vector unsigned short);
vector unsigned short vec_vsrah (vector unsigned short,
                                 vector unsigned short);

vector signed char vec_vsrab (vector signed char, vector unsigned char);
vector unsigned char vec_vsrab (vector unsigned char,
                                vector unsigned char);

vector signed int vec_srl (vector signed int, vector unsigned int);
vector signed int vec_srl (vector signed int, vector unsigned short);
vector signed int vec_srl (vector signed int, vector unsigned char);
vector unsigned int vec_srl (vector unsigned int, vector unsigned int);
vector unsigned int vec_srl (vector unsigned int,
                             vector unsigned short);
vector unsigned int vec_srl (vector unsigned int, vector unsigned char);
vector bool int vec_srl (vector bool int, vector unsigned int);
vector bool int vec_srl (vector bool int, vector unsigned short);
vector bool int vec_srl (vector bool int, vector unsigned char);
vector signed short vec_srl (vector signed short, vector unsigned int);
vector signed short vec_srl (vector signed short,
                             vector unsigned short);
vector signed short vec_srl (vector signed short, vector unsigned char);
vector unsigned short vec_srl (vector unsigned short,
                               vector unsigned int);
vector unsigned short vec_srl (vector unsigned short,
                               vector unsigned short);
vector unsigned short vec_srl (vector unsigned short,
                               vector unsigned char);
vector bool short vec_srl (vector bool short, vector unsigned int);
vector bool short vec_srl (vector bool short, vector unsigned short);
vector bool short vec_srl (vector bool short, vector unsigned char);
vector pixel vec_srl (vector pixel, vector unsigned int);
vector pixel vec_srl (vector pixel, vector unsigned short);
vector pixel vec_srl (vector pixel, vector unsigned char);
vector signed char vec_srl (vector signed char, vector unsigned int);
vector signed char vec_srl (vector signed char, vector unsigned short);
vector signed char vec_srl (vector signed char, vector unsigned char);
vector unsigned char vec_srl (vector unsigned char,
                              vector unsigned int);
vector unsigned char vec_srl (vector unsigned char,
                              vector unsigned short);
vector unsigned char vec_srl (vector unsigned char,
                              vector unsigned char);
vector bool char vec_srl (vector bool char, vector unsigned int);
vector bool char vec_srl (vector bool char, vector unsigned short);
vector bool char vec_srl (vector bool char, vector unsigned char);

vector float vec_sro (vector float, vector signed char);
vector float vec_sro (vector float, vector unsigned char);
vector signed int vec_sro (vector signed int, vector signed char);
vector signed int vec_sro (vector signed int, vector unsigned char);
vector unsigned int vec_sro (vector unsigned int, vector signed char);
vector unsigned int vec_sro (vector unsigned int, vector unsigned char);
vector signed short vec_sro (vector signed short, vector signed char);
vector signed short vec_sro (vector signed short, vector unsigned char);
vector unsigned short vec_sro (vector unsigned short,
                               vector signed char);
vector unsigned short vec_sro (vector unsigned short,
                               vector unsigned char);
vector pixel vec_sro (vector pixel, vector signed char);
vector pixel vec_sro (vector pixel, vector unsigned char);
vector signed char vec_sro (vector signed char, vector signed char);
vector signed char vec_sro (vector signed char, vector unsigned char);
vector unsigned char vec_sro (vector unsigned char, vector signed char);
vector unsigned char vec_sro (vector unsigned char,
                              vector unsigned char);

void vec_st (vector float, int, vector float *);
void vec_st (vector float, int, float *);
void vec_st (vector signed int, int, vector signed int *);
void vec_st (vector signed int, int, int *);
void vec_st (vector unsigned int, int, vector unsigned int *);
void vec_st (vector unsigned int, int, unsigned int *);
void vec_st (vector bool int, int, vector bool int *);
void vec_st (vector bool int, int, unsigned int *);
void vec_st (vector bool int, int, int *);
void vec_st (vector signed short, int, vector signed short *);
void vec_st (vector signed short, int, short *);
void vec_st (vector unsigned short, int, vector unsigned short *);
void vec_st (vector unsigned short, int, unsigned short *);
void vec_st (vector bool short, int, vector bool short *);
void vec_st (vector bool short, int, unsigned short *);
void vec_st (vector pixel, int, vector pixel *);
void vec_st (vector pixel, int, unsigned short *);
void vec_st (vector pixel, int, short *);
void vec_st (vector bool short, int, short *);
void vec_st (vector signed char, int, vector signed char *);
void vec_st (vector signed char, int, signed char *);
void vec_st (vector unsigned char, int, vector unsigned char *);
void vec_st (vector unsigned char, int, unsigned char *);
void vec_st (vector bool char, int, vector bool char *);
void vec_st (vector bool char, int, unsigned char *);
void vec_st (vector bool char, int, signed char *);

void vec_ste (vector signed char, int, signed char *);
void vec_ste (vector unsigned char, int, unsigned char *);
void vec_ste (vector bool char, int, signed char *);
void vec_ste (vector bool char, int, unsigned char *);
void vec_ste (vector signed short, int, short *);
void vec_ste (vector unsigned short, int, unsigned short *);
void vec_ste (vector bool short, int, short *);
void vec_ste (vector bool short, int, unsigned short *);
void vec_ste (vector pixel, int, short *);
void vec_ste (vector pixel, int, unsigned short *);
void vec_ste (vector float, int, float *);
void vec_ste (vector signed int, int, int *);
void vec_ste (vector unsigned int, int, unsigned int *);
void vec_ste (vector bool int, int, int *);
void vec_ste (vector bool int, int, unsigned int *);

void vec_stvewx (vector float, int, float *);
void vec_stvewx (vector signed int, int, int *);
void vec_stvewx (vector unsigned int, int, unsigned int *);
void vec_stvewx (vector bool int, int, int *);
void vec_stvewx (vector bool int, int, unsigned int *);

void vec_stvehx (vector signed short, int, short *);
void vec_stvehx (vector unsigned short, int, unsigned short *);
void vec_stvehx (vector bool short, int, short *);
void vec_stvehx (vector bool short, int, unsigned short *);
void vec_stvehx (vector pixel, int, short *);
void vec_stvehx (vector pixel, int, unsigned short *);

void vec_stvebx (vector signed char, int, signed char *);
void vec_stvebx (vector unsigned char, int, unsigned char *);
void vec_stvebx (vector bool char, int, signed char *);
void vec_stvebx (vector bool char, int, unsigned char *);

void vec_stl (vector float, int, vector float *);
void vec_stl (vector float, int, float *);
void vec_stl (vector signed int, int, vector signed int *);
void vec_stl (vector signed int, int, int *);
void vec_stl (vector unsigned int, int, vector unsigned int *);
void vec_stl (vector unsigned int, int, unsigned int *);
void vec_stl (vector bool int, int, vector bool int *);
void vec_stl (vector bool int, int, unsigned int *);
void vec_stl (vector bool int, int, int *);
void vec_stl (vector signed short, int, vector signed short *);
void vec_stl (vector signed short, int, short *);
void vec_stl (vector unsigned short, int, vector unsigned short *);
void vec_stl (vector unsigned short, int, unsigned short *);
void vec_stl (vector bool short, int, vector bool short *);
void vec_stl (vector bool short, int, unsigned short *);
void vec_stl (vector bool short, int, short *);
void vec_stl (vector pixel, int, vector pixel *);
void vec_stl (vector pixel, int, unsigned short *);
void vec_stl (vector pixel, int, short *);
void vec_stl (vector signed char, int, vector signed char *);
void vec_stl (vector signed char, int, signed char *);
void vec_stl (vector unsigned char, int, vector unsigned char *);
void vec_stl (vector unsigned char, int, unsigned char *);
void vec_stl (vector bool char, int, vector bool char *);
void vec_stl (vector bool char, int, unsigned char *);
void vec_stl (vector bool char, int, signed char *);

vector signed char vec_sub (vector bool char, vector signed char);
vector signed char vec_sub (vector signed char, vector bool char);
vector signed char vec_sub (vector signed char, vector signed char);
vector unsigned char vec_sub (vector bool char, vector unsigned char);
vector unsigned char vec_sub (vector unsigned char, vector bool char);
vector unsigned char vec_sub (vector unsigned char,
                              vector unsigned char);
vector signed short vec_sub (vector bool short, vector signed short);
vector signed short vec_sub (vector signed short, vector bool short);
vector signed short vec_sub (vector signed short, vector signed short);
vector unsigned short vec_sub (vector bool short,
                               vector unsigned short);
vector unsigned short vec_sub (vector unsigned short,
                               vector bool short);
vector unsigned short vec_sub (vector unsigned short,
                               vector unsigned short);
vector signed int vec_sub (vector bool int, vector signed int);
vector signed int vec_sub (vector signed int, vector bool int);
vector signed int vec_sub (vector signed int, vector signed int);
vector unsigned int vec_sub (vector bool int, vector unsigned int);
vector unsigned int vec_sub (vector unsigned int, vector bool int);
vector unsigned int vec_sub (vector unsigned int, vector unsigned int);
vector float vec_sub (vector float, vector float);

vector float vec_vsubfp (vector float, vector float);

vector signed int vec_vsubuwm (vector bool int, vector signed int);
vector signed int vec_vsubuwm (vector signed int, vector bool int);
vector signed int vec_vsubuwm (vector signed int, vector signed int);
vector unsigned int vec_vsubuwm (vector bool int, vector unsigned int);
vector unsigned int vec_vsubuwm (vector unsigned int, vector bool int);
vector unsigned int vec_vsubuwm (vector unsigned int,
                                 vector unsigned int);

vector signed short vec_vsubuhm (vector bool short,
                                 vector signed short);
vector signed short vec_vsubuhm (vector signed short,
                                 vector bool short);
vector signed short vec_vsubuhm (vector signed short,
                                 vector signed short);
vector unsigned short vec_vsubuhm (vector bool short,
                                   vector unsigned short);
vector unsigned short vec_vsubuhm (vector unsigned short,
                                   vector bool short);
vector unsigned short vec_vsubuhm (vector unsigned short,
                                   vector unsigned short);

vector signed char vec_vsububm (vector bool char, vector signed char);
vector signed char vec_vsububm (vector signed char, vector bool char);
vector signed char vec_vsububm (vector signed char, vector signed char);
vector unsigned char vec_vsububm (vector bool char,
                                  vector unsigned char);
vector unsigned char vec_vsububm (vector unsigned char,
                                  vector bool char);
vector unsigned char vec_vsububm (vector unsigned char,
                                  vector unsigned char);

vector unsigned int vec_subc (vector unsigned int, vector unsigned int);

vector unsigned char vec_subs (vector bool char, vector unsigned char);
vector unsigned char vec_subs (vector unsigned char, vector bool char);
vector unsigned char vec_subs (vector unsigned char,
                               vector unsigned char);
vector signed char vec_subs (vector bool char, vector signed char);
vector signed char vec_subs (vector signed char, vector bool char);
vector signed char vec_subs (vector signed char, vector signed char);
vector unsigned short vec_subs (vector bool short,
                                vector unsigned short);
vector unsigned short vec_subs (vector unsigned short,
                                vector bool short);
vector unsigned short vec_subs (vector unsigned short,
                                vector unsigned short);
vector signed short vec_subs (vector bool short, vector signed short);
vector signed short vec_subs (vector signed short, vector bool short);
vector signed short vec_subs (vector signed short, vector signed short);
vector unsigned int vec_subs (vector bool int, vector unsigned int);
vector unsigned int vec_subs (vector unsigned int, vector bool int);
vector unsigned int vec_subs (vector unsigned int, vector unsigned int);
vector signed int vec_subs (vector bool int, vector signed int);
vector signed int vec_subs (vector signed int, vector bool int);
vector signed int vec_subs (vector signed int, vector signed int);

vector signed int vec_vsubsws (vector bool int, vector signed int);
vector signed int vec_vsubsws (vector signed int, vector bool int);
vector signed int vec_vsubsws (vector signed int, vector signed int);

vector unsigned int vec_vsubuws (vector bool int, vector unsigned int);
vector unsigned int vec_vsubuws (vector unsigned int, vector bool int);
vector unsigned int vec_vsubuws (vector unsigned int,
                                 vector unsigned int);

vector signed short vec_vsubshs (vector bool short,
                                 vector signed short);
vector signed short vec_vsubshs (vector signed short,
                                 vector bool short);
vector signed short vec_vsubshs (vector signed short,
                                 vector signed short);

vector unsigned short vec_vsubuhs (vector bool short,
                                   vector unsigned short);
vector unsigned short vec_vsubuhs (vector unsigned short,
                                   vector bool short);
vector unsigned short vec_vsubuhs (vector unsigned short,
                                   vector unsigned short);

vector signed char vec_vsubsbs (vector bool char, vector signed char);
vector signed char vec_vsubsbs (vector signed char, vector bool char);
vector signed char vec_vsubsbs (vector signed char, vector signed char);

vector unsigned char vec_vsububs (vector bool char,
                                  vector unsigned char);
vector unsigned char vec_vsububs (vector unsigned char,
                                  vector bool char);
vector unsigned char vec_vsububs (vector unsigned char,
                                  vector unsigned char);

vector unsigned int vec_sum4s (vector unsigned char,
                               vector unsigned int);
vector signed int vec_sum4s (vector signed char, vector signed int);
vector signed int vec_sum4s (vector signed short, vector signed int);

vector signed int vec_vsum4shs (vector signed short, vector signed int);

vector signed int vec_vsum4sbs (vector signed char, vector signed int);

vector unsigned int vec_vsum4ubs (vector unsigned char,
                                  vector unsigned int);

vector signed int vec_sum2s (vector signed int, vector signed int);

vector signed int vec_sums (vector signed int, vector signed int);

vector float vec_trunc (vector float);

vector signed short vec_unpackh (vector signed char);
vector bool short vec_unpackh (vector bool char);
vector signed int vec_unpackh (vector signed short);
vector bool int vec_unpackh (vector bool short);
vector unsigned int vec_unpackh (vector pixel);

vector bool int vec_vupkhsh (vector bool short);
vector signed int vec_vupkhsh (vector signed short);

vector unsigned int vec_vupkhpx (vector pixel);

vector bool short vec_vupkhsb (vector bool char);
vector signed short vec_vupkhsb (vector signed char);

vector signed short vec_unpackl (vector signed char);
vector bool short vec_unpackl (vector bool char);
vector unsigned int vec_unpackl (vector pixel);
vector signed int vec_unpackl (vector signed short);
vector bool int vec_unpackl (vector bool short);

vector unsigned int vec_vupklpx (vector pixel);

vector bool int vec_vupklsh (vector bool short);
vector signed int vec_vupklsh (vector signed short);

vector bool short vec_vupklsb (vector bool char);
vector signed short vec_vupklsb (vector signed char);

vector float vec_xor (vector float, vector float);
vector float vec_xor (vector float, vector bool int);
vector float vec_xor (vector bool int, vector float);
vector bool int vec_xor (vector bool int, vector bool int);
vector signed int vec_xor (vector bool int, vector signed int);
vector signed int vec_xor (vector signed int, vector bool int);
vector signed int vec_xor (vector signed int, vector signed int);
vector unsigned int vec_xor (vector bool int, vector unsigned int);
vector unsigned int vec_xor (vector unsigned int, vector bool int);
vector unsigned int vec_xor (vector unsigned int, vector unsigned int);
vector bool short vec_xor (vector bool short, vector bool short);
vector signed short vec_xor (vector bool short, vector signed short);
vector signed short vec_xor (vector signed short, vector bool short);
vector signed short vec_xor (vector signed short, vector signed short);
vector unsigned short vec_xor (vector bool short,
                               vector unsigned short);
vector unsigned short vec_xor (vector unsigned short,
                               vector bool short);
vector unsigned short vec_xor (vector unsigned short,
                               vector unsigned short);
vector signed char vec_xor (vector bool char, vector signed char);
vector bool char vec_xor (vector bool char, vector bool char);
vector signed char vec_xor (vector signed char, vector bool char);
vector signed char vec_xor (vector signed char, vector signed char);
vector unsigned char vec_xor (vector bool char, vector unsigned char);
vector unsigned char vec_xor (vector unsigned char, vector bool char);
vector unsigned char vec_xor (vector unsigned char,
                              vector unsigned char);

int vec_all_eq (vector signed char, vector bool char);
int vec_all_eq (vector signed char, vector signed char);
int vec_all_eq (vector unsigned char, vector bool char);
int vec_all_eq (vector unsigned char, vector unsigned char);
int vec_all_eq (vector bool char, vector bool char);
int vec_all_eq (vector bool char, vector unsigned char);
int vec_all_eq (vector bool char, vector signed char);
int vec_all_eq (vector signed short, vector bool short);
int vec_all_eq (vector signed short, vector signed short);
int vec_all_eq (vector unsigned short, vector bool short);
int vec_all_eq (vector unsigned short, vector unsigned short);
int vec_all_eq (vector bool short, vector bool short);
int vec_all_eq (vector bool short, vector unsigned short);
int vec_all_eq (vector bool short, vector signed short);
int vec_all_eq (vector pixel, vector pixel);
int vec_all_eq (vector signed int, vector bool int);
int vec_all_eq (vector signed int, vector signed int);
int vec_all_eq (vector unsigned int, vector bool int);
int vec_all_eq (vector unsigned int, vector unsigned int);
int vec_all_eq (vector bool int, vector bool int);
int vec_all_eq (vector bool int, vector unsigned int);
int vec_all_eq (vector bool int, vector signed int);
int vec_all_eq (vector float, vector float);

int vec_all_ge (vector bool char, vector unsigned char);
int vec_all_ge (vector unsigned char, vector bool char);
int vec_all_ge (vector unsigned char, vector unsigned char);
int vec_all_ge (vector bool char, vector signed char);
int vec_all_ge (vector signed char, vector bool char);
int vec_all_ge (vector signed char, vector signed char);
int vec_all_ge (vector bool short, vector unsigned short);
int vec_all_ge (vector unsigned short, vector bool short);
int vec_all_ge (vector unsigned short, vector unsigned short);
int vec_all_ge (vector signed short, vector signed short);
int vec_all_ge (vector bool short, vector signed short);
int vec_all_ge (vector signed short, vector bool short);
int vec_all_ge (vector bool int, vector unsigned int);
int vec_all_ge (vector unsigned int, vector bool int);
int vec_all_ge (vector unsigned int, vector unsigned int);
int vec_all_ge (vector bool int, vector signed int);
int vec_all_ge (vector signed int, vector bool int);
int vec_all_ge (vector signed int, vector signed int);
int vec_all_ge (vector float, vector float);

int vec_all_gt (vector bool char, vector unsigned char);
int vec_all_gt (vector unsigned char, vector bool char);
int vec_all_gt (vector unsigned char, vector unsigned char);
int vec_all_gt (vector bool char, vector signed char);
int vec_all_gt (vector signed char, vector bool char);
int vec_all_gt (vector signed char, vector signed char);
int vec_all_gt (vector bool short, vector unsigned short);
int vec_all_gt (vector unsigned short, vector bool short);
int vec_all_gt (vector unsigned short, vector unsigned short);
int vec_all_gt (vector bool short, vector signed short);
int vec_all_gt (vector signed short, vector bool short);
int vec_all_gt (vector signed short, vector signed short);
int vec_all_gt (vector bool int, vector unsigned int);
int vec_all_gt (vector unsigned int, vector bool int);
int vec_all_gt (vector unsigned int, vector unsigned int);
int vec_all_gt (vector bool int, vector signed int);
int vec_all_gt (vector signed int, vector bool int);
int vec_all_gt (vector signed int, vector signed int);
int vec_all_gt (vector float, vector float);

int vec_all_in (vector float, vector float);

int vec_all_le (vector bool char, vector unsigned char);
int vec_all_le (vector unsigned char, vector bool char);
int vec_all_le (vector unsigned char, vector unsigned char);
int vec_all_le (vector bool char, vector signed char);
int vec_all_le (vector signed char, vector bool char);
int vec_all_le (vector signed char, vector signed char);
int vec_all_le (vector bool short, vector unsigned short);
int vec_all_le (vector unsigned short, vector bool short);
int vec_all_le (vector unsigned short, vector unsigned short);
int vec_all_le (vector bool short, vector signed short);
int vec_all_le (vector signed short, vector bool short);
int vec_all_le (vector signed short, vector signed short);
int vec_all_le (vector bool int, vector unsigned int);
int vec_all_le (vector unsigned int, vector bool int);
int vec_all_le (vector unsigned int, vector unsigned int);
int vec_all_le (vector bool int, vector signed int);
int vec_all_le (vector signed int, vector bool int);
int vec_all_le (vector signed int, vector signed int);
int vec_all_le (vector float, vector float);

int vec_all_lt (vector bool char, vector unsigned char);
int vec_all_lt (vector unsigned char, vector bool char);
int vec_all_lt (vector unsigned char, vector unsigned char);
int vec_all_lt (vector bool char, vector signed char);
int vec_all_lt (vector signed char, vector bool char);
int vec_all_lt (vector signed char, vector signed char);
int vec_all_lt (vector bool short, vector unsigned short);
int vec_all_lt (vector unsigned short, vector bool short);
int vec_all_lt (vector unsigned short, vector unsigned short);
int vec_all_lt (vector bool short, vector signed short);
int vec_all_lt (vector signed short, vector bool short);
int vec_all_lt (vector signed short, vector signed short);
int vec_all_lt (vector bool int, vector unsigned int);
int vec_all_lt (vector unsigned int, vector bool int);
int vec_all_lt (vector unsigned int, vector unsigned int);
int vec_all_lt (vector bool int, vector signed int);
int vec_all_lt (vector signed int, vector bool int);
int vec_all_lt (vector signed int, vector signed int);
int vec_all_lt (vector float, vector float);

int vec_all_nan (vector float);

int vec_all_ne (vector signed char, vector bool char);
int vec_all_ne (vector signed char, vector signed char);
int vec_all_ne (vector unsigned char, vector bool char);
int vec_all_ne (vector unsigned char, vector unsigned char);
int vec_all_ne (vector bool char, vector bool char);
int vec_all_ne (vector bool char, vector unsigned char);
int vec_all_ne (vector bool char, vector signed char);
int vec_all_ne (vector signed short, vector bool short);
int vec_all_ne (vector signed short, vector signed short);
int vec_all_ne (vector unsigned short, vector bool short);
int vec_all_ne (vector unsigned short, vector unsigned short);
int vec_all_ne (vector bool short, vector bool short);
int vec_all_ne (vector bool short, vector unsigned short);
int vec_all_ne (vector bool short, vector signed short);
int vec_all_ne (vector pixel, vector pixel);
int vec_all_ne (vector signed int, vector bool int);
int vec_all_ne (vector signed int, vector signed int);
int vec_all_ne (vector unsigned int, vector bool int);
int vec_all_ne (vector unsigned int, vector unsigned int);
int vec_all_ne (vector bool int, vector bool int);
int vec_all_ne (vector bool int, vector unsigned int);
int vec_all_ne (vector bool int, vector signed int);
int vec_all_ne (vector float, vector float);

int vec_all_nge (vector float, vector float);

int vec_all_ngt (vector float, vector float);

int vec_all_nle (vector float, vector float);

int vec_all_nlt (vector float, vector float);

int vec_all_numeric (vector float);

int vec_any_eq (vector signed char, vector bool char);
int vec_any_eq (vector signed char, vector signed char);
int vec_any_eq (vector unsigned char, vector bool char);
int vec_any_eq (vector unsigned char, vector unsigned char);
int vec_any_eq (vector bool char, vector bool char);
int vec_any_eq (vector bool char, vector unsigned char);
int vec_any_eq (vector bool char, vector signed char);
int vec_any_eq (vector signed short, vector bool short);
int vec_any_eq (vector signed short, vector signed short);
int vec_any_eq (vector unsigned short, vector bool short);
int vec_any_eq (vector unsigned short, vector unsigned short);
int vec_any_eq (vector bool short, vector bool short);
int vec_any_eq (vector bool short, vector unsigned short);
int vec_any_eq (vector bool short, vector signed short);
int vec_any_eq (vector pixel, vector pixel);
int vec_any_eq (vector signed int, vector bool int);
int vec_any_eq (vector signed int, vector signed int);
int vec_any_eq (vector unsigned int, vector bool int);
int vec_any_eq (vector unsigned int, vector unsigned int);
int vec_any_eq (vector bool int, vector bool int);
int vec_any_eq (vector bool int, vector unsigned int);
int vec_any_eq (vector bool int, vector signed int);
int vec_any_eq (vector float, vector float);

int vec_any_ge (vector signed char, vector bool char);
int vec_any_ge (vector unsigned char, vector bool char);
int vec_any_ge (vector unsigned char, vector unsigned char);
int vec_any_ge (vector signed char, vector signed char);
int vec_any_ge (vector bool char, vector unsigned char);
int vec_any_ge (vector bool char, vector signed char);
int vec_any_ge (vector unsigned short, vector bool short);
int vec_any_ge (vector unsigned short, vector unsigned short);
int vec_any_ge (vector signed short, vector signed short);
int vec_any_ge (vector signed short, vector bool short);
int vec_any_ge (vector bool short, vector unsigned short);
int vec_any_ge (vector bool short, vector signed short);
int vec_any_ge (vector signed int, vector bool int);
int vec_any_ge (vector unsigned int, vector bool int);
int vec_any_ge (vector unsigned int, vector unsigned int);
int vec_any_ge (vector signed int, vector signed int);
int vec_any_ge (vector bool int, vector unsigned int);
int vec_any_ge (vector bool int, vector signed int);
int vec_any_ge (vector float, vector float);

int vec_any_gt (vector bool char, vector unsigned char);
int vec_any_gt (vector unsigned char, vector bool char);
int vec_any_gt (vector unsigned char, vector unsigned char);
int vec_any_gt (vector bool char, vector signed char);
int vec_any_gt (vector signed char, vector bool char);
int vec_any_gt (vector signed char, vector signed char);
int vec_any_gt (vector bool short, vector unsigned short);
int vec_any_gt (vector unsigned short, vector bool short);
int vec_any_gt (vector unsigned short, vector unsigned short);
int vec_any_gt (vector bool short, vector signed short);
int vec_any_gt (vector signed short, vector bool short);
int vec_any_gt (vector signed short, vector signed short);
int vec_any_gt (vector bool int, vector unsigned int);
int vec_any_gt (vector unsigned int, vector bool int);
int vec_any_gt (vector unsigned int, vector unsigned int);
int vec_any_gt (vector bool int, vector signed int);
int vec_any_gt (vector signed int, vector bool int);
int vec_any_gt (vector signed int, vector signed int);
int vec_any_gt (vector float, vector float);

int vec_any_le (vector bool char, vector unsigned char);
int vec_any_le (vector unsigned char, vector bool char);
int vec_any_le (vector unsigned char, vector unsigned char);
int vec_any_le (vector bool char, vector signed char);
int vec_any_le (vector signed char, vector bool char);
int vec_any_le (vector signed char, vector signed char);
int vec_any_le (vector bool short, vector unsigned short);
int vec_any_le (vector unsigned short, vector bool short);
int vec_any_le (vector unsigned short, vector unsigned short);
int vec_any_le (vector bool short, vector signed short);
int vec_any_le (vector signed short, vector bool short);
int vec_any_le (vector signed short, vector signed short);
int vec_any_le (vector bool int, vector unsigned int);
int vec_any_le (vector unsigned int, vector bool int);
int vec_any_le (vector unsigned int, vector unsigned int);
int vec_any_le (vector bool int, vector signed int);
int vec_any_le (vector signed int, vector bool int);
int vec_any_le (vector signed int, vector signed int);
int vec_any_le (vector float, vector float);

int vec_any_lt (vector bool char, vector unsigned char);
int vec_any_lt (vector unsigned char, vector bool char);
int vec_any_lt (vector unsigned char, vector unsigned char);
int vec_any_lt (vector bool char, vector signed char);
int vec_any_lt (vector signed char, vector bool char);
int vec_any_lt (vector signed char, vector signed char);
int vec_any_lt (vector bool short, vector unsigned short);
int vec_any_lt (vector unsigned short, vector bool short);
int vec_any_lt (vector unsigned short, vector unsigned short);
int vec_any_lt (vector bool short, vector signed short);
int vec_any_lt (vector signed short, vector bool short);
int vec_any_lt (vector signed short, vector signed short);
int vec_any_lt (vector bool int, vector unsigned int);
int vec_any_lt (vector unsigned int, vector bool int);
int vec_any_lt (vector unsigned int, vector unsigned int);
int vec_any_lt (vector bool int, vector signed int);
int vec_any_lt (vector signed int, vector bool int);
int vec_any_lt (vector signed int, vector signed int);
int vec_any_lt (vector float, vector float);

int vec_any_nan (vector float);

int vec_any_ne (vector signed char, vector bool char);
int vec_any_ne (vector signed char, vector signed char);
int vec_any_ne (vector unsigned char, vector bool char);
int vec_any_ne (vector unsigned char, vector unsigned char);
int vec_any_ne (vector bool char, vector bool char);
int vec_any_ne (vector bool char, vector unsigned char);
int vec_any_ne (vector bool char, vector signed char);
int vec_any_ne (vector signed short, vector bool short);
int vec_any_ne (vector signed short, vector signed short);
int vec_any_ne (vector unsigned short, vector bool short);
int vec_any_ne (vector unsigned short, vector unsigned short);
int vec_any_ne (vector bool short, vector bool short);
int vec_any_ne (vector bool short, vector unsigned short);
int vec_any_ne (vector bool short, vector signed short);
int vec_any_ne (vector pixel, vector pixel);
int vec_any_ne (vector signed int, vector bool int);
int vec_any_ne (vector signed int, vector signed int);
int vec_any_ne (vector unsigned int, vector bool int);
int vec_any_ne (vector unsigned int, vector unsigned int);
int vec_any_ne (vector bool int, vector bool int);
int vec_any_ne (vector bool int, vector unsigned int);
int vec_any_ne (vector bool int, vector signed int);
int vec_any_ne (vector float, vector float);

int vec_any_nge (vector float, vector float);

int vec_any_ngt (vector float, vector float);

int vec_any_nle (vector float, vector float);

int vec_any_nlt (vector float, vector float);

int vec_any_numeric (vector float);

int vec_any_out (vector float, vector float);
@end smallexample

@node SPARC VIS Built-in Functions
@subsection SPARC VIS Built-in Functions

GCC supports SIMD operations on the SPARC using both the generic vector
extensions (@pxref{Vector Extensions}) as well as built-in functions for
the SPARC Visual Instruction Set (VIS).  When you use the @option{-mvis}
switch, the VIS extension is exposed as the following built-in functions:

@smallexample
typedef int v2si __attribute__ ((vector_size (8)));
typedef short v4hi __attribute__ ((vector_size (8)));
typedef short v2hi __attribute__ ((vector_size (4)));
typedef char v8qi __attribute__ ((vector_size (8)));
typedef char v4qi __attribute__ ((vector_size (4)));

void * __builtin_vis_alignaddr (void *, long);
int64_t __builtin_vis_faligndatadi (int64_t, int64_t);
v2si __builtin_vis_faligndatav2si (v2si, v2si);
v4hi __builtin_vis_faligndatav4hi (v4si, v4si);
v8qi __builtin_vis_faligndatav8qi (v8qi, v8qi);

v4hi __builtin_vis_fexpand (v4qi);

v4hi __builtin_vis_fmul8x16 (v4qi, v4hi);
v4hi __builtin_vis_fmul8x16au (v4qi, v4hi);
v4hi __builtin_vis_fmul8x16al (v4qi, v4hi);
v4hi __builtin_vis_fmul8sux16 (v8qi, v4hi);
v4hi __builtin_vis_fmul8ulx16 (v8qi, v4hi);
v2si __builtin_vis_fmuld8sux16 (v4qi, v2hi);
v2si __builtin_vis_fmuld8ulx16 (v4qi, v2hi);

v4qi __builtin_vis_fpack16 (v4hi);
v8qi __builtin_vis_fpack32 (v2si, v2si);
v2hi __builtin_vis_fpackfix (v2si);
v8qi __builtin_vis_fpmerge (v4qi, v4qi);

int64_t __builtin_vis_pdist (v8qi, v8qi, int64_t);
@end smallexample

@node Target Format Checks
@section Format Checks Specific to Particular Target Machines

For some target machines, GCC supports additional options to the
format attribute
(@pxref{Function Attributes,,Declaring Attributes of Functions}).

@menu
* Solaris Format Checks::
@end menu

@node Solaris Format Checks
@subsection Solaris Format Checks

Solaris targets support the @code{cmn_err} (or @code{__cmn_err__}) format
check.  @code{cmn_err} accepts a subset of the standard @code{printf}
conversions, and the two-argument @code{%b} conversion for displaying
bit-fields.  See the Solaris man page for @code{cmn_err} for more information.

@node Pragmas
@section Pragmas Accepted by GCC
@cindex pragmas
@cindex #pragma

GCC supports several types of pragmas, primarily in order to compile
code originally written for other compilers.  Note that in general
we do not recommend the use of pragmas; @xref{Function Attributes},
for further explanation.

@menu
* ARM Pragmas::
* M32C Pragmas::
* RS/6000 and PowerPC Pragmas::
* Darwin Pragmas::
* Solaris Pragmas::
* Symbol-Renaming Pragmas::
* Structure-Packing Pragmas::
* Weak Pragmas::
* Diagnostic Pragmas::
* Visibility Pragmas::
@end menu

@node ARM Pragmas
@subsection ARM Pragmas

The ARM target defines pragmas for controlling the default addition of
@code{long_call} and @code{short_call} attributes to functions.
@xref{Function Attributes}, for information about the effects of these
attributes.

@table @code
@item long_calls
@cindex pragma, long_calls
Set all subsequent functions to have the @code{long_call} attribute.

@item no_long_calls
@cindex pragma, no_long_calls
Set all subsequent functions to have the @code{short_call} attribute.

@item long_calls_off
@cindex pragma, long_calls_off
Do not affect the @code{long_call} or @code{short_call} attributes of
subsequent functions.
@end table

@node M32C Pragmas
@subsection M32C Pragmas

@table @code
@item memregs @var{number}
@cindex pragma, memregs
Overrides the command line option @code{-memregs=} for the current
file.  Use with care!  This pragma must be before any function in the
file, and mixing different memregs values in different objects may
make them incompatible.  This pragma is useful when a
performance-critical function uses a memreg for temporary values,
as it may allow you to reduce the number of memregs used.

@end table

@node RS/6000 and PowerPC Pragmas
@subsection RS/6000 and PowerPC Pragmas

The RS/6000 and PowerPC targets define one pragma for controlling
whether or not the @code{longcall} attribute is added to function
declarations by default.  This pragma overrides the @option{-mlongcall}
option, but not the @code{longcall} and @code{shortcall} attributes.
@xref{RS/6000 and PowerPC Options}, for more information about when long
calls are and are not necessary.

@table @code
@item longcall (1)
@cindex pragma, longcall
Apply the @code{longcall} attribute to all subsequent function
declarations.

@item longcall (0)
Do not apply the @code{longcall} attribute to subsequent function
declarations.
@end table

@c Describe c4x pragmas here.
@c Describe h8300 pragmas here.
@c Describe sh pragmas here.
@c Describe v850 pragmas here.

@node Darwin Pragmas
@subsection Darwin Pragmas

The following pragmas are available for all architectures running the
Darwin operating system.  These are useful for compatibility with other
Mac OS compilers.

@table @code
@item mark @var{tokens}@dots{}
@cindex pragma, mark
This pragma is accepted, but has no effect.

@item options align=@var{alignment}
@cindex pragma, options align
This pragma sets the alignment of fields in structures.  The values of
@var{alignment} may be @code{mac68k}, to emulate m68k alignment, or
@code{power}, to emulate PowerPC alignment.  Uses of this pragma nest
properly; to restore the previous setting, use @code{reset} for the
@var{alignment}.

@item segment @var{tokens}@dots{}
@cindex pragma, segment
This pragma is accepted, but has no effect.

@item unused (@var{var} [, @var{var}]@dots{})
@cindex pragma, unused
This pragma declares variables to be possibly unused.  GCC will not
produce warnings for the listed variables.  The effect is similar to
that of the @code{unused} attribute, except that this pragma may appear
anywhere within the variables' scopes.
@end table

@node Solaris Pragmas
@subsection Solaris Pragmas

The Solaris target supports @code{#pragma redefine_extname}
(@pxref{Symbol-Renaming Pragmas}).  It also supports additional
@code{#pragma} directives for compatibility with the system compiler.

@table @code
@item align @var{alignment} (@var{variable} [, @var{variable}]...)
@cindex pragma, align

Increase the minimum alignment of each @var{variable} to @var{alignment}.
This is the same as GCC's @code{aligned} attribute @pxref{Variable
Attributes}).  Macro expansion occurs on the arguments to this pragma
when compiling C and Objective-C.  It does not currently occur when
compiling C++, but this is a bug which may be fixed in a future
release.

@item fini (@var{function} [, @var{function}]...)
@cindex pragma, fini

This pragma causes each listed @var{function} to be called after
main, or during shared module unloading, by adding a call to the
@code{.fini} section.

@item init (@var{function} [, @var{function}]...)
@cindex pragma, init

This pragma causes each listed @var{function} to be called during
initialization (before @code{main}) or during shared module loading, by
adding a call to the @code{.init} section.

@end table

@node Symbol-Renaming Pragmas
@subsection Symbol-Renaming Pragmas

For compatibility with the Solaris and Tru64 UNIX system headers, GCC
supports two @code{#pragma} directives which change the name used in
assembly for a given declaration.  These pragmas are only available on
platforms whose system headers need them.  To get this effect on all
platforms supported by GCC, use the asm labels extension (@pxref{Asm
Labels}).

@table @code
@item redefine_extname @var{oldname} @var{newname}
@cindex pragma, redefine_extname

This pragma gives the C function @var{oldname} the assembly symbol
@var{newname}.  The preprocessor macro @code{__PRAGMA_REDEFINE_EXTNAME}
will be defined if this pragma is available (currently only on
Solaris).

@item extern_prefix @var{string}
@cindex pragma, extern_prefix

This pragma causes all subsequent external function and variable
declarations to have @var{string} prepended to their assembly symbols.
This effect may be terminated with another @code{extern_prefix} pragma
whose argument is an empty string.  The preprocessor macro
@code{__PRAGMA_EXTERN_PREFIX} will be defined if this pragma is
available (currently only on Tru64 UNIX)@.
@end table

These pragmas and the asm labels extension interact in a complicated
manner.  Here are some corner cases you may want to be aware of.

@enumerate
@item Both pragmas silently apply only to declarations with external
linkage.  Asm labels do not have this restriction.

@item In C++, both pragmas silently apply only to declarations with
``C'' linkage.  Again, asm labels do not have this restriction.

@item If any of the three ways of changing the assembly name of a
declaration is applied to a declaration whose assembly name has
already been determined (either by a previous use of one of these
features, or because the compiler needed the assembly name in order to
generate code), and the new name is different, a warning issues and
the name does not change.

@item The @var{oldname} used by @code{#pragma redefine_extname} is
always the C-language name.

@item If @code{#pragma extern_prefix} is in effect, and a declaration
occurs with an asm label attached, the prefix is silently ignored for
that declaration.

@item If @code{#pragma extern_prefix} and @code{#pragma redefine_extname}
apply to the same declaration, whichever triggered first wins, and a
warning issues if they contradict each other.  (We would like to have
@code{#pragma redefine_extname} always win, for consistency with asm
labels, but if @code{#pragma extern_prefix} triggers first we have no
way of knowing that that happened.)
@end enumerate

@node Structure-Packing Pragmas
@subsection Structure-Packing Pragmas

For compatibility with Win32, GCC supports a set of @code{#pragma}
directives which change the maximum alignment of members of structures
(other than zero-width bitfields), unions, and classes subsequently
defined.  The @var{n} value below always is required to be a small power
of two and specifies the new alignment in bytes.

@enumerate
@item @code{#pragma pack(@var{n})} simply sets the new alignment.
@item @code{#pragma pack()} sets the alignment to the one that was in
effect when compilation started (see also command line option
@option{-fpack-struct[=<n>]} @pxref{Code Gen Options}).
@item @code{#pragma pack(push[,@var{n}])} pushes the current alignment
setting on an internal stack and then optionally sets the new alignment.
@item @code{#pragma pack(pop)} restores the alignment setting to the one
saved at the top of the internal stack (and removes that stack entry).
Note that @code{#pragma pack([@var{n}])} does not influence this internal
stack; thus it is possible to have @code{#pragma pack(push)} followed by
multiple @code{#pragma pack(@var{n})} instances and finalized by a single
@code{#pragma pack(pop)}.
@end enumerate

Some targets, e.g. i386 and powerpc, support the @code{ms_struct}
@code{#pragma} which lays out a structure as the documented
@code{__attribute__ ((ms_struct))}.
@enumerate
@item @code{#pragma ms_struct on} turns on the layout for structures
declared.
@item @code{#pragma ms_struct off} turns off the layout for structures
declared.
@item @code{#pragma ms_struct reset} goes back to the default layout.
@end enumerate

@node Weak Pragmas
@subsection Weak Pragmas

For compatibility with SVR4, GCC supports a set of @code{#pragma}
directives for declaring symbols to be weak, and defining weak
aliases.

@table @code
@item #pragma weak @var{symbol}
@cindex pragma, weak
This pragma declares @var{symbol} to be weak, as if the declaration
had the attribute of the same name.  The pragma may appear before
or after the declaration of @var{symbol}, but must appear before
either its first use or its definition.  It is not an error for
@var{symbol} to never be defined at all.

@item #pragma weak @var{symbol1} = @var{symbol2}
This pragma declares @var{symbol1} to be a weak alias of @var{symbol2}.
It is an error if @var{symbol2} is not defined in the current
translation unit.
@end table

@node Diagnostic Pragmas
@subsection Diagnostic Pragmas

GCC allows the user to selectively enable or disable certain types of
diagnostics, and change the kind of the diagnostic.  For example, a
project's policy might require that all sources compile with
@option{-Werror} but certain files might have exceptions allowing
specific types of warnings.  Or, a project might selectively enable
diagnostics and treat them as errors depending on which preprocessor
macros are defined.

@table @code
@item #pragma GCC diagnostic @var{kind} @var{option}
@cindex pragma, diagnostic

Modifies the disposition of a diagnostic.  Note that not all
diagnostics are modifiable; at the moment only warnings (normally
controlled by @samp{-W...}) can be controlled, and not all of them.
Use @option{-fdiagnostics-show-option} to determine which diagnostics
are controllable and which option controls them.

@var{kind} is @samp{error} to treat this diagnostic as an error,
@samp{warning} to treat it like a warning (even if @option{-Werror} is
in effect), or @samp{ignored} if the diagnostic is to be ignored.
@var{option} is a double quoted string which matches the command line
option.

@example
#pragma GCC diagnostic warning "-Wformat"
#pragma GCC diagnostic error "-Wformat"
#pragma GCC diagnostic ignored "-Wformat"
@end example

Note that these pragmas override any command line options.  Also,
while it is syntactically valid to put these pragmas anywhere in your
sources, the only supported location for them is before any data or
functions are defined.  Doing otherwise may result in unpredictable
results depending on how the optimizer manages your sources.  If the
same option is listed multiple times, the last one specified is the
one that is in effect.  This pragma is not intended to be a general
purpose replacement for command line options, but for implementing
strict control over project policies.

@end table

@node Visibility Pragmas
@subsection Visibility Pragmas

@table @code
@item #pragma GCC visibility push(@var{visibility})
@itemx #pragma GCC visibility pop
@cindex pragma, visibility

This pragma allows the user to set the visibility for multiple
declarations without having to give each a visibility attribute
@xref{Function Attributes}, for more information about visibility and
the attribute syntax.

In C++, @samp{#pragma GCC visibility} affects only namespace-scope
declarations.  Class members and template specializations are not
affected; if you want to override the visibility for a particular
member or instantiation, you must use an attribute.

@end table

@node Unnamed Fields
@section Unnamed struct/union fields within structs/unions
@cindex struct
@cindex union

For compatibility with other compilers, GCC allows you to define
a structure or union that contains, as fields, structures and unions
without names.  For example:

@smallexample
struct @{
  int a;
  union @{
    int b;
    float c;
  @};
  int d;
@} foo;
@end smallexample

In this example, the user would be able to access members of the unnamed
union with code like @samp{foo.b}.  Note that only unnamed structs and
unions are allowed, you may not have, for example, an unnamed
@code{int}.

You must never create such structures that cause ambiguous field definitions.
For example, this structure:

@smallexample
struct @{
  int a;
  struct @{
    int a;
  @};
@} foo;
@end smallexample

It is ambiguous which @code{a} is being referred to with @samp{foo.a}.
Such constructs are not supported and must be avoided.  In the future,
such constructs may be detected and treated as compilation errors.

@opindex fms-extensions
Unless @option{-fms-extensions} is used, the unnamed field must be a
structure or union definition without a tag (for example, @samp{struct
@{ int a; @};}).  If @option{-fms-extensions} is used, the field may
also be a definition with a tag such as @samp{struct foo @{ int a;
@};}, a reference to a previously defined structure or union such as
@samp{struct foo;}, or a reference to a @code{typedef} name for a
previously defined structure or union type.

@node Thread-Local
@section Thread-Local Storage
@cindex Thread-Local Storage
@cindex @acronym{TLS}
@cindex __thread

Thread-local storage (@acronym{TLS}) is a mechanism by which variables
are allocated such that there is one instance of the variable per extant
thread.  The run-time model GCC uses to implement this originates
in the IA-64 processor-specific ABI, but has since been migrated
to other processors as well.  It requires significant support from
the linker (@command{ld}), dynamic linker (@command{ld.so}), and
system libraries (@file{libc.so} and @file{libpthread.so}), so it
is not available everywhere.

At the user level, the extension is visible with a new storage
class keyword: @code{__thread}.  For example:

@smallexample
__thread int i;
extern __thread struct state s;
static __thread char *p;
@end smallexample

The @code{__thread} specifier may be used alone, with the @code{extern}
or @code{static} specifiers, but with no other storage class specifier.
When used with @code{extern} or @code{static}, @code{__thread} must appear
immediately after the other storage class specifier.

The @code{__thread} specifier may be applied to any global, file-scoped
static, function-scoped static, or static data member of a class.  It may
not be applied to block-scoped automatic or non-static data member.

When the address-of operator is applied to a thread-local variable, it is
evaluated at run-time and returns the address of the current thread's
instance of that variable.  An address so obtained may be used by any
thread.  When a thread terminates, any pointers to thread-local variables
in that thread become invalid.

No static initialization may refer to the address of a thread-local variable.

In C++, if an initializer is present for a thread-local variable, it must
be a @var{constant-expression}, as defined in 5.19.2 of the ANSI/ISO C++
standard.

See @uref{http://people.redhat.com/drepper/tls.pdf,
ELF Handling For Thread-Local Storage} for a detailed explanation of
the four thread-local storage addressing models, and how the run-time
is expected to function.

@menu
* C99 Thread-Local Edits::
* C++98 Thread-Local Edits::
@end menu

@node C99 Thread-Local Edits
@subsection ISO/IEC 9899:1999 Edits for Thread-Local Storage

The following are a set of changes to ISO/IEC 9899:1999 (aka C99)
that document the exact semantics of the language extension.

@itemize @bullet
@item
@cite{5.1.2  Execution environments}

Add new text after paragraph 1

@quotation
Within either execution environment, a @dfn{thread} is a flow of
control within a program.  It is implementation defined whether
or not there may be more than one thread associated with a program.
It is implementation defined how threads beyond the first are
created, the name and type of the function called at thread
startup, and how threads may be terminated.  However, objects
with thread storage duration shall be initialized before thread
startup.
@end quotation

@item
@cite{6.2.4  Storage durations of objects}

Add new text before paragraph 3

@quotation
An object whose identifier is declared with the storage-class
specifier @w{@code{__thread}} has @dfn{thread storage duration}.
Its lifetime is the entire execution of the thread, and its
stored value is initialized only once, prior to thread startup.
@end quotation

@item
@cite{6.4.1  Keywords}

Add @code{__thread}.

@item
@cite{6.7.1  Storage-class specifiers}

Add @code{__thread} to the list of storage class specifiers in
paragraph 1.

Change paragraph 2 to

@quotation
With the exception of @code{__thread}, at most one storage-class
specifier may be given [@dots{}].  The @code{__thread} specifier may
be used alone, or immediately following @code{extern} or
@code{static}.
@end quotation

Add new text after paragraph 6

@quotation
The declaration of an identifier for a variable that has
block scope that specifies @code{__thread} shall also
specify either @code{extern} or @code{static}.

The @code{__thread} specifier shall be used only with
variables.
@end quotation
@end itemize

@node C++98 Thread-Local Edits
@subsection ISO/IEC 14882:1998 Edits for Thread-Local Storage

The following are a set of changes to ISO/IEC 14882:1998 (aka C++98)
that document the exact semantics of the language extension.

@itemize @bullet
@item
@b{[intro.execution]}

New text after paragraph 4

@quotation
A @dfn{thread} is a flow of control within the abstract machine.
It is implementation defined whether or not there may be more than
one thread.
@end quotation

New text after paragraph 7

@quotation
It is unspecified whether additional action must be taken to
ensure when and whether side effects are visible to other threads.
@end quotation

@item
@b{[lex.key]}

Add @code{__thread}.

@item
@b{[basic.start.main]}

Add after paragraph 5

@quotation
The thread that begins execution at the @code{main} function is called
the @dfn{main thread}.  It is implementation defined how functions
beginning threads other than the main thread are designated or typed.
A function so designated, as well as the @code{main} function, is called
a @dfn{thread startup function}.  It is implementation defined what
happens if a thread startup function returns.  It is implementation
defined what happens to other threads when any thread calls @code{exit}.
@end quotation

@item
@b{[basic.start.init]}

Add after paragraph 4

@quotation
The storage for an object of thread storage duration shall be
statically initialized before the first statement of the thread startup
function.  An object of thread storage duration shall not require
dynamic initialization.
@end quotation

@item
@b{[basic.start.term]}

Add after paragraph 3

@quotation
The type of an object with thread storage duration shall not have a
non-trivial destructor, nor shall it be an array type whose elements
(directly or indirectly) have non-trivial destructors.
@end quotation

@item
@b{[basic.stc]}

Add ``thread storage duration'' to the list in paragraph 1.

Change paragraph 2

@quotation
Thread, static, and automatic storage durations are associated with
objects introduced by declarations [@dots{}].
@end quotation

Add @code{__thread} to the list of specifiers in paragraph 3.

@item
@b{[basic.stc.thread]}

New section before @b{[basic.stc.static]}

@quotation
The keyword @code{__thread} applied to a non-local object gives the
object thread storage duration.

A local variable or class data member declared both @code{static}
and @code{__thread} gives the variable or member thread storage
duration.
@end quotation

@item
@b{[basic.stc.static]}

Change paragraph 1

@quotation
All objects which have neither thread storage duration, dynamic
storage duration nor are local [@dots{}].
@end quotation

@item
@b{[dcl.stc]}

Add @code{__thread} to the list in paragraph 1.

Change paragraph 1

@quotation
With the exception of @code{__thread}, at most one
@var{storage-class-specifier} shall appear in a given
@var{decl-specifier-seq}.  The @code{__thread} specifier may
be used alone, or immediately following the @code{extern} or
@code{static} specifiers.  [@dots{}]
@end quotation

Add after paragraph 5

@quotation
The @code{__thread} specifier can be applied only to the names of objects
and to anonymous unions.
@end quotation

@item
@b{[class.mem]}

Add after paragraph 6

@quotation
Non-@code{static} members shall not be @code{__thread}.
@end quotation
@end itemize

@node C++ Extensions
@chapter Extensions to the C++ Language
@cindex extensions, C++ language
@cindex C++ language extensions

The GNU compiler provides these extensions to the C++ language (and you
can also use most of the C language extensions in your C++ programs).  If you
want to write code that checks whether these features are available, you can
test for the GNU compiler the same way as for C programs: check for a
predefined macro @code{__GNUC__}.  You can also use @code{__GNUG__} to
test specifically for GNU C++ (@pxref{Common Predefined Macros,,
Predefined Macros,cpp,The GNU C Preprocessor}).

@menu
* Volatiles::		What constitutes an access to a volatile object.
* Restricted Pointers:: C99 restricted pointers and references.
* Vague Linkage::       Where G++ puts inlines, vtables and such.
* C++ Interface::       You can use a single C++ header file for both
                        declarations and definitions.
* Template Instantiation:: Methods for ensuring that exactly one copy of
                        each needed template instantiation is emitted.
* Bound member functions:: You can extract a function pointer to the
                        method denoted by a @samp{->*} or @samp{.*} expression.
* C++ Attributes::      Variable, function, and type attributes for C++ only.
* Namespace Association:: Strong using-directives for namespace association.
* Java Exceptions::     Tweaking exception handling to work with Java.
* Deprecated Features:: Things will disappear from g++.
* Backwards Compatibility:: Compatibilities with earlier definitions of C++.
@end menu

@node Volatiles
@section When is a Volatile Object Accessed?
@cindex accessing volatiles
@cindex volatile read
@cindex volatile write
@cindex volatile access

Both the C and C++ standard have the concept of volatile objects.  These
are normally accessed by pointers and used for accessing hardware.  The
standards encourage compilers to refrain from optimizations concerning
accesses to volatile objects.  The C standard leaves it implementation
defined  as to what constitutes a volatile access.  The C++ standard omits
to specify this, except to say that C++ should behave in a similar manner
to C with respect to volatiles, where possible.  The minimum either
standard specifies is that at a sequence point all previous accesses to
volatile objects have stabilized and no subsequent accesses have
occurred.  Thus an implementation is free to reorder and combine
volatile accesses which occur between sequence points, but cannot do so
for accesses across a sequence point.  The use of volatiles does not
allow you to violate the restriction on updating objects multiple times
within a sequence point.

@xref{Qualifiers implementation, , Volatile qualifier and the C compiler}.

The behavior differs slightly between C and C++ in the non-obvious cases:

@smallexample
volatile int *src = @var{somevalue};
*src;
@end smallexample

With C, such expressions are rvalues, and GCC interprets this either as a
read of the volatile object being pointed to or only as request to evaluate
the side-effects.  The C++ standard specifies that such expressions do not
undergo lvalue to rvalue conversion, and that the type of the dereferenced
object may be incomplete.  The C++ standard does not specify explicitly
that it is this lvalue to rvalue conversion which may be responsible for
causing an access.  However, there is reason to believe that it is,
because otherwise certain simple expressions become undefined.  However,
because it would surprise most programmers, G++ treats dereferencing a
pointer to volatile object of complete type when the value is unused as
GCC would do for an equivalent type in C.  When the object has incomplete
type, G++ issues a warning; if you wish to force an error, you must
force a conversion to rvalue with, for instance, a static cast.

When using a reference to volatile, G++ does not treat equivalent
expressions as accesses to volatiles, but instead issues a warning that
no volatile is accessed.  The rationale for this is that otherwise it
becomes difficult to determine where volatile access occur, and not
possible to ignore the return value from functions returning volatile
references.  Again, if you wish to force a read, cast the reference to
an rvalue.

@node Restricted Pointers
@section Restricting Pointer Aliasing
@cindex restricted pointers
@cindex restricted references
@cindex restricted this pointer

As with the C front end, G++ understands the C99 feature of restricted pointers,
specified with the @code{__restrict__}, or @code{__restrict} type
qualifier.  Because you cannot compile C++ by specifying the @option{-std=c99}
language flag, @code{restrict} is not a keyword in C++.

In addition to allowing restricted pointers, you can specify restricted
references, which indicate that the reference is not aliased in the local
context.

@smallexample
void fn (int *__restrict__ rptr, int &__restrict__ rref)
@{
  /* @r{@dots{}} */
@}
@end smallexample

@noindent
In the body of @code{fn}, @var{rptr} points to an unaliased integer and
@var{rref} refers to a (different) unaliased integer.

You may also specify whether a member function's @var{this} pointer is
unaliased by using @code{__restrict__} as a member function qualifier.

@smallexample
void T::fn () __restrict__
@{
  /* @r{@dots{}} */
@}
@end smallexample

@noindent
Within the body of @code{T::fn}, @var{this} will have the effective
definition @code{T *__restrict__ const this}.  Notice that the
interpretation of a @code{__restrict__} member function qualifier is
different to that of @code{const} or @code{volatile} qualifier, in that it
is applied to the pointer rather than the object.  This is consistent with
other compilers which implement restricted pointers.

As with all outermost parameter qualifiers, @code{__restrict__} is
ignored in function definition matching.  This means you only need to
specify @code{__restrict__} in a function definition, rather than
in a function prototype as well.

@node Vague Linkage
@section Vague Linkage
@cindex vague linkage

There are several constructs in C++ which require space in the object
file but are not clearly tied to a single translation unit.  We say that
these constructs have ``vague linkage''.  Typically such constructs are
emitted wherever they are needed, though sometimes we can be more
clever.

@table @asis
@item Inline Functions
Inline functions are typically defined in a header file which can be
included in many different compilations.  Hopefully they can usually be
inlined, but sometimes an out-of-line copy is necessary, if the address
of the function is taken or if inlining fails.  In general, we emit an
out-of-line copy in all translation units where one is needed.  As an
exception, we only emit inline virtual functions with the vtable, since
it will always require a copy.

Local static variables and string constants used in an inline function
are also considered to have vague linkage, since they must be shared
between all inlined and out-of-line instances of the function.

@item VTables
@cindex vtable
C++ virtual functions are implemented in most compilers using a lookup
table, known as a vtable.  The vtable contains pointers to the virtual
functions provided by a class, and each object of the class contains a
pointer to its vtable (or vtables, in some multiple-inheritance
situations).  If the class declares any non-inline, non-pure virtual
functions, the first one is chosen as the ``key method'' for the class,
and the vtable is only emitted in the translation unit where the key
method is defined.

@emph{Note:} If the chosen key method is later defined as inline, the
vtable will still be emitted in every translation unit which defines it.
Make sure that any inline virtuals are declared inline in the class
body, even if they are not defined there.

@item type_info objects
@cindex type_info
@cindex RTTI
C++ requires information about types to be written out in order to
implement @samp{dynamic_cast}, @samp{typeid} and exception handling.
For polymorphic classes (classes with virtual functions), the type_info
object is written out along with the vtable so that @samp{dynamic_cast}
can determine the dynamic type of a class object at runtime.  For all
other types, we write out the type_info object when it is used: when
applying @samp{typeid} to an expression, throwing an object, or
referring to a type in a catch clause or exception specification.

@item Template Instantiations
Most everything in this section also applies to template instantiations,
but there are other options as well.
@xref{Template Instantiation,,Where's the Template?}.

@end table

When used with GNU ld version 2.8 or later on an ELF system such as
GNU/Linux or Solaris 2, or on Microsoft Windows, duplicate copies of
these constructs will be discarded at link time.  This is known as
COMDAT support.

On targets that don't support COMDAT, but do support weak symbols, GCC
will use them.  This way one copy will override all the others, but
the unused copies will still take up space in the executable.

For targets which do not support either COMDAT or weak symbols,
most entities with vague linkage will be emitted as local symbols to
avoid duplicate definition errors from the linker.  This will not happen
for local statics in inlines, however, as having multiple copies will
almost certainly break things.

@xref{C++ Interface,,Declarations and Definitions in One Header}, for
another way to control placement of these constructs.

@node C++ Interface
@section #pragma interface and implementation

@cindex interface and implementation headers, C++
@cindex C++ interface and implementation headers
@cindex pragmas, interface and implementation

@code{#pragma interface} and @code{#pragma implementation} provide the
user with a way of explicitly directing the compiler to emit entities
with vague linkage (and debugging information) in a particular
translation unit.

@emph{Note:} As of GCC 2.7.2, these @code{#pragma}s are not useful in
most cases, because of COMDAT support and the ``key method'' heuristic
mentioned in @ref{Vague Linkage}.  Using them can actually cause your
program to grow due to unnecessary out-of-line copies of inline
functions.  Currently (3.4) the only benefit of these
@code{#pragma}s is reduced duplication of debugging information, and
that should be addressed soon on DWARF 2 targets with the use of
COMDAT groups.

@table @code
@item #pragma interface
@itemx #pragma interface "@var{subdir}/@var{objects}.h"
@kindex #pragma interface
Use this directive in @emph{header files} that define object classes, to save
space in most of the object files that use those classes.  Normally,
local copies of certain information (backup copies of inline member
functions, debugging information, and the internal tables that implement
virtual functions) must be kept in each object file that includes class
definitions.  You can use this pragma to avoid such duplication.  When a
header file containing @samp{#pragma interface} is included in a
compilation, this auxiliary information will not be generated (unless
the main input source file itself uses @samp{#pragma implementation}).
Instead, the object files will contain references to be resolved at link
time.

The second form of this directive is useful for the case where you have
multiple headers with the same name in different directories.  If you
use this form, you must specify the same string to @samp{#pragma
implementation}.

@item #pragma implementation
@itemx #pragma implementation "@var{objects}.h"
@kindex #pragma implementation
Use this pragma in a @emph{main input file}, when you want full output from
included header files to be generated (and made globally visible).  The
included header file, in turn, should use @samp{#pragma interface}.
Backup copies of inline member functions, debugging information, and the
internal tables used to implement virtual functions are all generated in
implementation files.

@cindex implied @code{#pragma implementation}
@cindex @code{#pragma implementation}, implied
@cindex naming convention, implementation headers
If you use @samp{#pragma implementation} with no argument, it applies to
an include file with the same basename@footnote{A file's @dfn{basename}
was the name stripped of all leading path information and of trailing
suffixes, such as @samp{.h} or @samp{.C} or @samp{.cc}.} as your source
file.  For example, in @file{allclass.cc}, giving just
@samp{#pragma implementation}
by itself is equivalent to @samp{#pragma implementation "allclass.h"}.

In versions of GNU C++ prior to 2.6.0 @file{allclass.h} was treated as
an implementation file whenever you would include it from
@file{allclass.cc} even if you never specified @samp{#pragma
implementation}.  This was deemed to be more trouble than it was worth,
however, and disabled.

Use the string argument if you want a single implementation file to
include code from multiple header files.  (You must also use
@samp{#include} to include the header file; @samp{#pragma
implementation} only specifies how to use the file---it doesn't actually
include it.)

There is no way to split up the contents of a single header file into
multiple implementation files.
@end table

@cindex inlining and C++ pragmas
@cindex C++ pragmas, effect on inlining
@cindex pragmas in C++, effect on inlining
@samp{#pragma implementation} and @samp{#pragma interface} also have an
effect on function inlining.

If you define a class in a header file marked with @samp{#pragma
interface}, the effect on an inline function defined in that class is
similar to an explicit @code{extern} declaration---the compiler emits
no code at all to define an independent version of the function.  Its
definition is used only for inlining with its callers.

@opindex fno-implement-inlines
Conversely, when you include the same header file in a main source file
that declares it as @samp{#pragma implementation}, the compiler emits
code for the function itself; this defines a version of the function
that can be found via pointers (or by callers compiled without
inlining).  If all calls to the function can be inlined, you can avoid
emitting the function by compiling with @option{-fno-implement-inlines}.
If any calls were not inlined, you will get linker errors.

@node Template Instantiation
@section Where's the Template?
@cindex template instantiation

C++ templates are the first language feature to require more
intelligence from the environment than one usually finds on a UNIX
system.  Somehow the compiler and linker have to make sure that each
template instance occurs exactly once in the executable if it is needed,
and not at all otherwise.  There are two basic approaches to this
problem, which are referred to as the Borland model and the Cfront model.

@table @asis
@item Borland model
Borland C++ solved the template instantiation problem by adding the code
equivalent of common blocks to their linker; the compiler emits template
instances in each translation unit that uses them, and the linker
collapses them together.  The advantage of this model is that the linker
only has to consider the object files themselves; there is no external
complexity to worry about.  This disadvantage is that compilation time
is increased because the template code is being compiled repeatedly.
Code written for this model tends to include definitions of all
templates in the header file, since they must be seen to be
instantiated.

@item Cfront model
The AT&T C++ translator, Cfront, solved the template instantiation
problem by creating the notion of a template repository, an
automatically maintained place where template instances are stored.  A
more modern version of the repository works as follows: As individual
object files are built, the compiler places any template definitions and
instantiations encountered in the repository.  At link time, the link
wrapper adds in the objects in the repository and compiles any needed
instances that were not previously emitted.  The advantages of this
model are more optimal compilation speed and the ability to use the
system linker; to implement the Borland model a compiler vendor also
needs to replace the linker.  The disadvantages are vastly increased
complexity, and thus potential for error; for some code this can be
just as transparent, but in practice it can been very difficult to build
multiple programs in one directory and one program in multiple
directories.  Code written for this model tends to separate definitions
of non-inline member templates into a separate file, which should be
compiled separately.
@end table

When used with GNU ld version 2.8 or later on an ELF system such as
GNU/Linux or Solaris 2, or on Microsoft Windows, G++ supports the
Borland model.  On other systems, G++ implements neither automatic
model.

A future version of G++ will support a hybrid model whereby the compiler
will emit any instantiations for which the template definition is
included in the compile, and store template definitions and
instantiation context information into the object file for the rest.
The link wrapper will extract that information as necessary and invoke
the compiler to produce the remaining instantiations.  The linker will
then combine duplicate instantiations.

In the mean time, you have the following options for dealing with
template instantiations:

@enumerate
@item
@opindex frepo
Compile your template-using code with @option{-frepo}.  The compiler will
generate files with the extension @samp{.rpo} listing all of the
template instantiations used in the corresponding object files which
could be instantiated there; the link wrapper, @samp{collect2}, will
then update the @samp{.rpo} files to tell the compiler where to place
those instantiations and rebuild any affected object files.  The
link-time overhead is negligible after the first pass, as the compiler
will continue to place the instantiations in the same files.

This is your best option for application code written for the Borland
model, as it will just work.  Code written for the Cfront model will
need to be modified so that the template definitions are available at
one or more points of instantiation; usually this is as simple as adding
@code{#include <tmethods.cc>} to the end of each template header.

For library code, if you want the library to provide all of the template
instantiations it needs, just try to link all of its object files
together; the link will fail, but cause the instantiations to be
generated as a side effect.  Be warned, however, that this may cause
conflicts if multiple libraries try to provide the same instantiations.
For greater control, use explicit instantiation as described in the next
option.

@item
@opindex fno-implicit-templates
Compile your code with @option{-fno-implicit-templates} to disable the
implicit generation of template instances, and explicitly instantiate
all the ones you use.  This approach requires more knowledge of exactly
which instances you need than do the others, but it's less
mysterious and allows greater control.  You can scatter the explicit
instantiations throughout your program, perhaps putting them in the
translation units where the instances are used or the translation units
that define the templates themselves; you can put all of the explicit
instantiations you need into one big file; or you can create small files
like

@smallexample
#include "Foo.h"
#include "Foo.cc"

template class Foo<int>;
template ostream& operator <<
                (ostream&, const Foo<int>&);
@end smallexample

for each of the instances you need, and create a template instantiation
library from those.

If you are using Cfront-model code, you can probably get away with not
using @option{-fno-implicit-templates} when compiling files that don't
@samp{#include} the member template definitions.

If you use one big file to do the instantiations, you may want to
compile it without @option{-fno-implicit-templates} so you get all of the
instances required by your explicit instantiations (but not by any
other files) without having to specify them as well.

G++ has extended the template instantiation syntax given in the ISO
standard to allow forward declaration of explicit instantiations
(with @code{extern}), instantiation of the compiler support data for a
template class (i.e.@: the vtable) without instantiating any of its
members (with @code{inline}), and instantiation of only the static data
members of a template class, without the support data or member
functions (with (@code{static}):

@smallexample
extern template int max (int, int);
inline template class Foo<int>;
static template class Foo<int>;
@end smallexample

@item
Do nothing.  Pretend G++ does implement automatic instantiation
management.  Code written for the Borland model will work fine, but
each translation unit will contain instances of each of the templates it
uses.  In a large program, this can lead to an unacceptable amount of code
duplication.
@end enumerate

@node Bound member functions
@section Extracting the function pointer from a bound pointer to member function
@cindex pmf
@cindex pointer to member function
@cindex bound pointer to member function

In C++, pointer to member functions (PMFs) are implemented using a wide
pointer of sorts to handle all the possible call mechanisms; the PMF
needs to store information about how to adjust the @samp{this} pointer,
and if the function pointed to is virtual, where to find the vtable, and
where in the vtable to look for the member function.  If you are using
PMFs in an inner loop, you should really reconsider that decision.  If
that is not an option, you can extract the pointer to the function that
would be called for a given object/PMF pair and call it directly inside
the inner loop, to save a bit of time.

Note that you will still be paying the penalty for the call through a
function pointer; on most modern architectures, such a call defeats the
branch prediction features of the CPU@.  This is also true of normal
virtual function calls.

The syntax for this extension is

@smallexample
extern A a;
extern int (A::*fp)();
typedef int (*fptr)(A *);

fptr p = (fptr)(a.*fp);
@end smallexample

For PMF constants (i.e.@: expressions of the form @samp{&Klasse::Member}),
no object is needed to obtain the address of the function.  They can be
converted to function pointers directly:

@smallexample
fptr p1 = (fptr)(&A::foo);
@end smallexample

@opindex Wno-pmf-conversions
You must specify @option{-Wno-pmf-conversions} to use this extension.

@node C++ Attributes
@section C++-Specific Variable, Function, and Type Attributes

Some attributes only make sense for C++ programs.

@table @code
@item init_priority (@var{priority})
@cindex init_priority attribute


In Standard C++, objects defined at namespace scope are guaranteed to be
initialized in an order in strict accordance with that of their definitions
@emph{in a given translation unit}.  No guarantee is made for initializations
across translation units.  However, GNU C++ allows users to control the
order of initialization of objects defined at namespace scope with the
@code{init_priority} attribute by specifying a relative @var{priority},
a constant integral expression currently bounded between 101 and 65535
inclusive.  Lower numbers indicate a higher priority.

In the following example, @code{A} would normally be created before
@code{B}, but the @code{init_priority} attribute has reversed that order:

@smallexample
Some_Class  A  __attribute__ ((init_priority (2000)));
Some_Class  B  __attribute__ ((init_priority (543)));
@end smallexample

@noindent
Note that the particular values of @var{priority} do not matter; only their
relative ordering.

@item java_interface
@cindex java_interface attribute

This type attribute informs C++ that the class is a Java interface.  It may
only be applied to classes declared within an @code{extern "Java"} block.
Calls to methods declared in this interface will be dispatched using GCJ's
interface table mechanism, instead of regular virtual table dispatch.

@end table

See also @xref{Namespace Association}.

@node Namespace Association
@section Namespace Association

@strong{Caution:} The semantics of this extension are not fully
defined.  Users should refrain from using this extension as its
semantics may change subtly over time.  It is possible that this
extension will be removed in future versions of G++.

A using-directive with @code{__attribute ((strong))} is stronger
than a normal using-directive in two ways:

@itemize @bullet
@item
Templates from the used namespace can be specialized and explicitly
instantiated as though they were members of the using namespace.

@item
The using namespace is considered an associated namespace of all
templates in the used namespace for purposes of argument-dependent
name lookup.
@end itemize

The used namespace must be nested within the using namespace so that
normal unqualified lookup works properly.

This is useful for composing a namespace transparently from
implementation namespaces.  For example:

@smallexample
namespace std @{
  namespace debug @{
    template <class T> struct A @{ @};
  @}
  using namespace debug __attribute ((__strong__));
  template <> struct A<int> @{ @};   // @r{ok to specialize}

  template <class T> void f (A<T>);
@}

int main()
@{
  f (std::A<float>());             // @r{lookup finds} std::f
  f (std::A<int>());
@}
@end smallexample

@node Java Exceptions
@section Java Exceptions

The Java language uses a slightly different exception handling model
from C++.  Normally, GNU C++ will automatically detect when you are
writing C++ code that uses Java exceptions, and handle them
appropriately.  However, if C++ code only needs to execute destructors
when Java exceptions are thrown through it, GCC will guess incorrectly.
Sample problematic code is:

@smallexample
  struct S @{ ~S(); @};
  extern void bar();    // @r{is written in Java, and may throw exceptions}
  void foo()
  @{
    S s;
    bar();
  @}
@end smallexample

@noindent
The usual effect of an incorrect guess is a link failure, complaining of
a missing routine called @samp{__gxx_personality_v0}.

You can inform the compiler that Java exceptions are to be used in a
translation unit, irrespective of what it might think, by writing
@samp{@w{#pragma GCC java_exceptions}} at the head of the file.  This
@samp{#pragma} must appear before any functions that throw or catch
exceptions, or run destructors when exceptions are thrown through them.

You cannot mix Java and C++ exceptions in the same translation unit.  It
is believed to be safe to throw a C++ exception from one file through
another file compiled for the Java exception model, or vice versa, but
there may be bugs in this area.

@node Deprecated Features
@section Deprecated Features

In the past, the GNU C++ compiler was extended to experiment with new
features, at a time when the C++ language was still evolving.  Now that
the C++ standard is complete, some of those features are superseded by
superior alternatives.  Using the old features might cause a warning in
some cases that the feature will be dropped in the future.  In other
cases, the feature might be gone already.

While the list below is not exhaustive, it documents some of the options
that are now deprecated:

@table @code
@item -fexternal-templates
@itemx -falt-external-templates
These are two of the many ways for G++ to implement template
instantiation.  @xref{Template Instantiation}.  The C++ standard clearly
defines how template definitions have to be organized across
implementation units.  G++ has an implicit instantiation mechanism that
should work just fine for standard-conforming code.

@item -fstrict-prototype
@itemx -fno-strict-prototype
Previously it was possible to use an empty prototype parameter list to
indicate an unspecified number of parameters (like C), rather than no
parameters, as C++ demands.  This feature has been removed, except where
it is required for backwards compatibility @xref{Backwards Compatibility}.
@end table

G++ allows a virtual function returning @samp{void *} to be overridden
by one returning a different pointer type.  This extension to the
covariant return type rules is now deprecated and will be removed from a
future version.

The G++ minimum and maximum operators (@samp{<?} and @samp{>?}) and
their compound forms (@samp{<?=}) and @samp{>?=}) have been deprecated
and will be removed in a future version.  Code using these operators
should be modified to use @code{std::min} and @code{std::max} instead.

The named return value extension has been deprecated, and is now
removed from G++.

The use of initializer lists with new expressions has been deprecated,
and is now removed from G++.

Floating and complex non-type template parameters have been deprecated,
and are now removed from G++.

The implicit typename extension has been deprecated and is now
removed from G++.

The use of default arguments in function pointers, function typedefs
and other places where they are not permitted by the standard is
deprecated and will be removed from a future version of G++.

G++ allows floating-point literals to appear in integral constant expressions,
e.g. @samp{ enum E @{ e = int(2.2 * 3.7) @} }
This extension is deprecated and will be removed from a future version.

G++ allows static data members of const floating-point type to be declared
with an initializer in a class definition. The standard only allows
initializers for static members of const integral types and const
enumeration types so this extension has been deprecated and will be removed
from a future version.

@node Backwards Compatibility
@section Backwards Compatibility
@cindex Backwards Compatibility
@cindex ARM [Annotated C++ Reference Manual]

Now that there is a definitive ISO standard C++, G++ has a specification
to adhere to.  The C++ language evolved over time, and features that
used to be acceptable in previous drafts of the standard, such as the ARM
[Annotated C++ Reference Manual], are no longer accepted.  In order to allow
compilation of C++ written to such drafts, G++ contains some backwards
compatibilities.  @emph{All such backwards compatibility features are
liable to disappear in future versions of G++.} They should be considered
deprecated @xref{Deprecated Features}.

@table @code
@item For scope
If a variable is declared at for scope, it used to remain in scope until
the end of the scope which contained the for statement (rather than just
within the for scope).  G++ retains this, but issues a warning, if such a
variable is accessed outside the for scope.

@item Implicit C language
Old C system header files did not contain an @code{extern "C" @{@dots{}@}}
scope to set the language.  On such systems, all header files are
implicitly scoped inside a C language scope.  Also, an empty prototype
@code{()} will be treated as an unspecified number of arguments, rather
than no arguments, as C++ demands.
@end table