initial import of GCC 12.3.0.

major changes in GCC 11 included:

- The default mode for C++ is now -std=gnu++17 instead of -std=gnu++14.
- When building GCC itself, the host compiler must now support C++11,
rather than C++98.
- Some short options of the gcov tool have been renamed: -i to -j and
-j to -H.
- ThreadSanitizer improvements.
- Introduce Hardware-assisted AddressSanitizer support.
- For targets that produce DWARF debugging information GCC now defaults
to DWARF version 5. This can produce up to 25% more compact debug
information compared to earlier versions.
- Many optimisations.
- The existing malloc attribute has been extended so that it can be
used to identify allocator/deallocator API pairs. A pair of new
-Wmismatched-dealloc and -Wmismatched-new-delete warnings are added.
- Other new warnings:
-Wsizeof-array-div, enabled by -Wall, warns about divisions of two
sizeof operators when the first one is applied to an array and the
divisor does not equal the size of the array element.
-Wstringop-overread, enabled by default, warns about calls to string
functions reading past the end of the arrays passed to them as
arguments.
-Wtsan, enabled by default, warns about unsupported features in
ThreadSanitizer (currently std::atomic_thread_fence).
- Enchanced warnings:
-Wfree-nonheap-object detects many more instances of calls to
deallocation functions with pointers not returned from a dynamic
memory allocation function.
-Wmaybe-uninitialized diagnoses passing pointers or references to
uninitialized memory to functions taking const-qualified arguments.
-Wuninitialized detects reads from uninitialized dynamically
allocated memory.
-Warray-parameter warns about functions with inconsistent array forms.
-Wvla-parameter warns about functions with inconsistent VLA forms.
- Several new features from the upcoming C2X revision of the ISO C
standard are supported with -std=c2x and -std=gnu2x.
- Several C++20 features have been implemented.
- The C++ front end has experimental support for some of the upcoming
C++23 draft.
- Several new C++ warnings.
- Enhanced Arm, AArch64, x86, and RISC-V CPU support.
- The implementation of how program state is tracked within
-fanalyzer has been completely rewritten with many enhancements.

see https://gcc.gnu.org/gcc-11/changes.html for a full list.

major changes in GCC 12 include:

- An ABI incompatibility between C and C++ when passing or returning
by value certain aggregates containing zero width bit-fields has
been discovered on various targets. x86-64, ARM and AArch64
will always ignore them (so there is a C ABI incompatibility
between GCC 11 and earlier with GCC 12 or later), PowerPC64 ELFv2
always take them into account (so there is a C++ ABI
incompatibility, GCC 4.4 and earlier compatible with GCC 12 or
later, incompatible with GCC 4.5 through GCC 11). RISC-V has
changed the handling of these already starting with GCC 10. As
the ABI requires, MIPS takes them into account handling function
return values so there is a C++ ABI incompatibility with GCC 4.5
through 11.
- STABS: Support for emitting the STABS debugging format is
deprecated and will be removed in the next release. All ports now
default to emit DWARF (version 2 or later) debugging info or are
obsoleted.
- Vectorization is enabled at -O2 which is now equivalent to the
original -O2 -ftree-vectorize -fvect-cost-model=very-cheap.
- GCC now supports the ShadowCallStack sanitizer.
- Support for __builtin_shufflevector compatible with the clang
language extension was added.
- Support for attribute unavailable was added.
- Support for __builtin_dynamic_object_size compatible with the
clang language extension was added.
- New warnings:
-Wbidi-chars warns about potentially misleading UTF-8
bidirectional control characters.
-Warray-compare warns about comparisons between two operands of
array type.
- Some new features from the upcoming C2X revision of the ISO C
standard are supported with -std=c2x and -std=gnu2x.
- Several C++23 features have been implemented.
- Many C++ enhancements across warnings and -f options.

see https://gcc.gnu.org/gcc-12/changes.html for a full list.

initial import of GCC 9.3.0. changes include:

- live patching support
- shell completion help
- generally better diagnostic output (less verbose/more useful)
- diagnostics and optimisation choices can be emitted in json
- asan memory usage reduction
- many general, and specific to switch, inter-procedure,
profile and link-time optimisations. from the release notes:
"Overall compile time of Firefox 66 and LibreOffice 6.2.3 on
an 8-core machine was reduced by about 5% compared to GCC 8.3"
- OpenMP 5.0 support
- better spell-guesser
- partial experimental support for c2x and c++2a
- c++17 is no longer experimental
- arm AAPCS GCC 6-8 structure passing bug fixed, may cause
incompatibility (restored compat with GCC 5 and earlier.)
- openrisc support

import GCC 6.4.0. see this url for details which are too large to
include here:

http://gcc.gnu.org/gcc-6/changes.html

the main visible changes appear to be:

- The default mode for C++ is now -std=gnu++14 instead of -std=gnu++98.
- The C and C++ compilers now support attributes on enumerators.
- Diagnostics can now contain "fix-it hints"
- more warnings (some added to -Wall)

import GCC 5.3.0. see these urls for details which are too large to
include here:

http://gcc.gnu.org/gcc-4.9/changes.html
http://gcc.gnu.org/gcc-5/changes.html

(note that GCC 5.x is a release stream like GCC 4.9.x, 4.8.x, etc.)


the main issues we will have are:

The default mode for C is now -std=gnu11 instead of -std=gnu89.

ARM:
The deprecated option -mwords-little-endian has been removed.
The options -mapcs, -mapcs-frame, -mtpcs-frame and -mtpcs-leaf-frame
which are only applicable to the old ABI have been deprecated.

MIPS:
The o32 ABI has been modified and extended. The o32 64-bit
floating-point register support is now obsolete and has been removed.
It has been replaced by three ABI extensions FPXX, FP64A, and FP64.
The meaning of the -mfp64 command-line option has changed. It is now
used to enable the FP64A and FP64 ABI extensions.

initial import of GCC 9.3.0. changes include:

- live patching support
- shell completion help
- generally better diagnostic output (less verbose/more useful)
- diagnostics and optimisation choices can be emitted in json
- asan memory usage reduction
- many general, and specific to switch, inter-procedure,
profile and link-time optimisations. from the release notes:
"Overall compile time of Firefox 66 and LibreOffice 6.2.3 on
an 8-core machine was reduced by about 5% compared to GCC 8.3"
- OpenMP 5.0 support
- better spell-guesser
- partial experimental support for c2x and c++2a
- c++17 is no longer experimental
- arm AAPCS GCC 6-8 structure passing bug fixed, may cause
incompatibility (restored compat with GCC 5 and earlier.)
- openrisc support

import GCC 6.4.0. see this url for details which are too large to
include here:

http://gcc.gnu.org/gcc-6/changes.html

the main visible changes appear to be:

- The default mode for C++ is now -std=gnu++14 instead of -std=gnu++98.
- The C and C++ compilers now support attributes on enumerators.
- Diagnostics can now contain "fix-it hints"
- more warnings (some added to -Wall)

import GCC 5.3.0. see these urls for details which are too large to
include here:

http://gcc.gnu.org/gcc-4.9/changes.html
http://gcc.gnu.org/gcc-5/changes.html

(note that GCC 5.x is a release stream like GCC 4.9.x, 4.8.x, etc.)


the main issues we will have are:

The default mode for C is now -std=gnu11 instead of -std=gnu89.

ARM:
The deprecated option -mwords-little-endian has been removed.
The options -mapcs, -mapcs-frame, -mtpcs-frame and -mtpcs-leaf-frame
which are only applicable to the old ABI have been deprecated.

MIPS:
The o32 ABI has been modified and extended. The o32 64-bit
floating-point register support is now obsolete and has been removed.
It has been replaced by three ABI extensions FPXX, FP64A, and FP64.
The meaning of the -mfp64 command-line option has changed. It is now
used to enable the FP64A and FP64 ABI extensions.

import GCC 6.4.0. see this url for details which are too large to
include here:

http://gcc.gnu.org/gcc-6/changes.html

the main visible changes appear to be:

- The default mode for C++ is now -std=gnu++14 instead of -std=gnu++98.
- The C and C++ compilers now support attributes on enumerators.
- Diagnostics can now contain "fix-it hints"
- more warnings (some added to -Wall)

import GCC 5.3.0. see these urls for details which are too large to
include here:

http://gcc.gnu.org/gcc-4.9/changes.html
http://gcc.gnu.org/gcc-5/changes.html

(note that GCC 5.x is a release stream like GCC 4.9.x, 4.8.x, etc.)


the main issues we will have are:

The default mode for C is now -std=gnu11 instead of -std=gnu89.

ARM:
The deprecated option -mwords-little-endian has been removed.
The options -mapcs, -mapcs-frame, -mtpcs-frame and -mtpcs-leaf-frame
which are only applicable to the old ABI have been deprecated.

MIPS:
The o32 ABI has been modified and extended. The o32 64-bit
floating-point register support is now obsolete and has been removed.
It has been replaced by three ABI extensions FPXX, FP64A, and FP64.
The meaning of the -mfp64 command-line option has changed. It is now
used to enable the FP64A and FP64 ABI extensions.

import GCC 5.3.0. see these urls for details which are too large to
include here:

http://gcc.gnu.org/gcc-4.9/changes.html
http://gcc.gnu.org/gcc-5/changes.html

(note that GCC 5.x is a release stream like GCC 4.9.x, 4.8.x, etc.)


the main issues we will have are:

The default mode for C is now -std=gnu11 instead of -std=gnu89.

ARM:
The deprecated option -mwords-little-endian has been removed.
The options -mapcs, -mapcs-frame, -mtpcs-frame and -mtpcs-leaf-frame
which are only applicable to the old ABI have been deprecated.

MIPS:
The o32 ABI has been modified and extended. The o32 64-bit
floating-point register support is now obsolete and has been removed.
It has been replaced by three ABI extensions FPXX, FP64A, and FP64.
The meaning of the -mfp64 command-line option has changed. It is now
used to enable the FP64A and FP64 ABI extensions.