Compiler.h revision 221345 
1//===-- llvm/Support/Compiler.h - Compiler abstraction support --*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file defines several macros, based on the current compiler.  This allows
11// use of compiler-specific features in a way that remains portable.
12//
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_SUPPORT_COMPILER_H
16#define LLVM_SUPPORT_COMPILER_H
17
18#ifndef __has_feature
19# define __has_feature(x) 0
20#endif
21
22/// LLVM_LIBRARY_VISIBILITY - If a class marked with this attribute is linked
23/// into a shared library, then the class should be private to the library and
24/// not accessible from outside it.  Can also be used to mark variables and
25/// functions, making them private to any shared library they are linked into.
26#if (__GNUC__ >= 4) && !defined(__MINGW32__) && !defined(__CYGWIN__)
27#define LLVM_LIBRARY_VISIBILITY __attribute__ ((visibility("hidden")))
28#else
29#define LLVM_LIBRARY_VISIBILITY
30#endif
31
32#if (__GNUC__ >= 4 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 1))
33#define LLVM_ATTRIBUTE_USED __attribute__((__used__))
34#else
35#define LLVM_ATTRIBUTE_USED
36#endif
37
38// Some compilers warn about unused functions. When a function is sometimes
39// used or not depending on build settings (e.g. a function only called from
40// within "assert"), this attribute can be used to suppress such warnings.
41//
42// However, it shouldn't be used for unused *variables*, as those have a much
43// more portable solution:
44//   (void)unused_var_name;
45// Prefer cast-to-void wherever it is sufficient.
46#if (__GNUC__ >= 4 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 1))
47#define LLVM_ATTRIBUTE_UNUSED __attribute__((__unused__))
48#else
49#define LLVM_ATTRIBUTE_UNUSED
50#endif
51
52#ifdef __GNUC__ // aka 'ATTRIBUTE_CONST' but following LLVM Conventions.
53#define LLVM_ATTRIBUTE_READNONE __attribute__((__const__))
54#else
55#define LLVM_ATTRIBUTE_READNONE
56#endif
57
58#ifdef __GNUC__  // aka 'ATTRIBUTE_PURE' but following LLVM Conventions.
59#define LLVM_ATTRIBUTE_READONLY __attribute__((__pure__))
60#else
61#define LLVM_ATTRIBUTE_READONLY
62#endif
63
64#if (__GNUC__ >= 4)
65#define BUILTIN_EXPECT(EXPR, VALUE) __builtin_expect((EXPR), (VALUE))
66#else
67#define BUILTIN_EXPECT(EXPR, VALUE) (EXPR)
68#endif
69
70// C++ doesn't support 'extern template' of template specializations.  GCC does,
71// but requires __extension__ before it.  In the header, use this:
72//   EXTERN_TEMPLATE_INSTANTIATION(class foo<bar>);
73// in the .cpp file, use this:
74//   TEMPLATE_INSTANTIATION(class foo<bar>);
75#ifdef __GNUC__
76#define EXTERN_TEMPLATE_INSTANTIATION(X) __extension__ extern template X
77#define TEMPLATE_INSTANTIATION(X) template X
78#else
79#define EXTERN_TEMPLATE_INSTANTIATION(X)
80#define TEMPLATE_INSTANTIATION(X)
81#endif
82
83// LLVM_ATTRIBUTE_NOINLINE - On compilers where we have a directive to do so,
84// mark a method "not for inlining".
85#if (__GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
86#define LLVM_ATTRIBUTE_NOINLINE __attribute__((noinline))
87#elif defined(_MSC_VER)
88#define LLVM_ATTRIBUTE_NOINLINE __declspec(noinline)
89#else
90#define LLVM_ATTRIBUTE_NOINLINE
91#endif
92
93// LLVM_ATTRIBUTE_ALWAYS_INLINE - On compilers where we have a directive to do
94// so, mark a method "always inline" because it is performance sensitive. GCC
95// 3.4 supported this but is buggy in various cases and produces unimplemented
96// errors, just use it in GCC 4.0 and later.
97#if __GNUC__ > 3
98#define LLVM_ATTRIBUTE_ALWAYS_INLINE __attribute__((always_inline))
99#elif defined(_MSC_VER)
100#define LLVM_ATTRIBUTE_ALWAYS_INLINE __forceinline
101#else
102#define LLVM_ATTRIBUTE_ALWAYS_INLINE
103#endif
104
105
106#ifdef __GNUC__
107#define LLVM_ATTRIBUTE_NORETURN __attribute__((noreturn))
108#elif defined(_MSC_VER)
109#define LLVM_ATTRIBUTE_NORETURN __declspec(noreturn)
110#else
111#define LLVM_ATTRIBUTE_NORETURN
112#endif
113
114// LLVM_ATTRIBUTE_DEPRECATED(decl, "message")
115#if __has_feature(attribute_deprecated_with_message)
116# define LLVM_ATTRIBUTE_DEPRECATED(decl, message) \
117  decl __attribute__((deprecated(message)))
118#elif defined(__GNUC__)
119# define LLVM_ATTRIBUTE_DEPRECATED(decl, message) \
120  decl __attribute__((deprecated))
121#elif defined(_MSC_VER)
122# define LLVM_ATTRIBUTE_DEPRECATED(decl, message) \
123  __declspec(deprecated(message)) decl
124#else
125# define LLVM_ATTRIBUTE_DEPRECATED(decl, message) \
126  decl
127#endif
128
129// LLVM_BUILTIN_UNREACHABLE - On compilers which support it, expands
130// to an expression which states that it is undefined behavior for the
131// compiler to reach this point.  Otherwise is not defined.
132#if defined(__clang__) || (__GNUC__ > 4) \
133 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 5)
134# define LLVM_BUILTIN_UNREACHABLE __builtin_unreachable()
135#endif
136
137#endif
138