1 //===-- Common internal contructs -------------------------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #ifndef LLVM_LIBC_SUPPORT_COMMON_H
10 #define LLVM_LIBC_SUPPORT_COMMON_H
11 
12 #define LIBC_INLINE_ASM __asm__ __volatile__
13 
14 #ifndef likely
15 #define likely(x) __builtin_expect(!!(x), 1)
16 #endif
17 #ifndef unlikely
18 #define unlikely(x) __builtin_expect(x, 0)
19 #endif
20 #ifndef UNUSED
21 #define UNUSED __attribute__((unused))
22 #endif
23 
24 #ifndef LLVM_LIBC_FUNCTION_ATTR
25 #define LLVM_LIBC_FUNCTION_ATTR
26 #endif
27 
28 // MacOS needs to be excluded because it does not support aliasing.
29 #if defined(LLVM_LIBC_PUBLIC_PACKAGING) && (!defined(__APPLE__))
30 #define LLVM_LIBC_FUNCTION(type, name, arglist)                                \
31   LLVM_LIBC_FUNCTION_ATTR decltype(__llvm_libc::name)                          \
32       __##name##_impl__ __asm__(#name);                                        \
33   decltype(__llvm_libc::name) name [[gnu::alias(#name)]];                      \
34   type __##name##_impl__ arglist
35 #else
36 #define LLVM_LIBC_FUNCTION(type, name, arglist) type name arglist
37 #endif
38 
39 namespace __llvm_libc {
40 namespace internal {
41 constexpr bool same_string(char const *lhs, char const *rhs) {
42   for (; *lhs || *rhs; ++lhs, ++rhs)
43     if (*lhs != *rhs)
44       return false;
45   return true;
46 }
47 } // namespace internal
48 } // namespace __llvm_libc
49 
50 // LLVM_LIBC_IS_DEFINED checks whether a particular macro is defined.
51 // Usage: constexpr bool kUseAvx = LLVM_LIBC_IS_DEFINED(__AVX__);
52 //
53 // This works by comparing the stringified version of the macro with and without
54 // evaluation. If FOO is not undefined both stringifications yield "FOO". If FOO
55 // is defined, one stringification yields "FOO" while the other yields its
56 // stringified value "1".
57 #define LLVM_LIBC_IS_DEFINED(macro)                                            \
58   !__llvm_libc::internal::same_string(                                         \
59       LLVM_LIBC_IS_DEFINED__EVAL_AND_STRINGIZE(macro), #macro)
60 #define LLVM_LIBC_IS_DEFINED__EVAL_AND_STRINGIZE(s) #s
61 
62 #endif // LLVM_LIBC_SUPPORT_COMMON_H
63