1//===-- Portable attributes -------------------------------------*- 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// This header file defines a set of macros for checking the presence of
9// important compiler and platform features. Such macros can be used to
10// produce portable code by parameterizing compilation based on the presence or
11// lack of a given feature.
12
13#ifndef LLVM_LIBC_SRC___SUPPORT_MACROS_CONFIG_H
14#define LLVM_LIBC_SRC___SUPPORT_MACROS_CONFIG_H
15
16#include "src/__support/macros/properties/architectures.h"
17#include "src/__support/macros/properties/compiler.h"
18
19#ifdef LIBC_COMPILER_IS_MSVC
20#include <intrin.h>
21#endif // LIBC_COMPILER_IS_MSVC
22
23// Workaround for compilers that do not support builtin detection.
24// FIXME: This is only required for the GPU portion which should be moved.
25#ifndef __has_builtin
26#define __has_builtin(b) 0
27#endif
28
29// Compiler feature-detection.
30// clang.llvm.org/docs/LanguageExtensions.html#has-feature-and-has-extension
31#ifdef __has_feature
32#define LIBC_HAS_FEATURE(f) __has_feature(f)
33#else
34#define LIBC_HAS_FEATURE(f) 0
35#endif
36
37#ifdef LIBC_COMPILER_IS_MSVC
38
39// __builtin_trap replacement
40#ifdef LIBC_TARGET_ARCH_IS_X86
41#define __builtin_trap __ud2
42#else // arm64
43#define __builtin_trap() __break(1)
44#endif
45
46#define __builtin_expect(value, expectation) (value)
47#define __builtin_unreachable() __assume(0)
48
49#define __builtin_prefetch(X, Y, Z)
50
51#define LIBC_HAS_BUILTIN_IS_CONSTANT_EVALUATED 1
52
53#endif // LIBC_COMPILER_IS_MSVC
54
55#ifdef __clang__
56// Declare a LIBC_NAMESPACE with hidden visibility. `namespace
57// LIBC_NAMESPACE_DECL {` should be used around all declarations and definitions
58// for libc internals as opposed to just `namespace LIBC_NAMESPACE {`. This
59// ensures that all declarations within this namespace have hidden
60// visibility, which optimizes codegen for uses of symbols defined in other
61// translation units in ways that can be necessary for correctness by avoiding
62// dynamic relocations. This does not affect the public C symbols which are
63// controlled independently via `LLVM_LIBC_FUNCTION_ATTR`.
64#define LIBC_NAMESPACE_DECL [[gnu::visibility("hidden")]] LIBC_NAMESPACE
65#else
66// TODO(#98548): GCC emits a warning when using the visibility attribute which
67// needs to be diagnosed and addressed.
68#define LIBC_NAMESPACE_DECL LIBC_NAMESPACE
69#endif
70
71// IMPORTANT (USE WITH CAUTION): This macro is intended to be used at the top of
72// the file and set to 1. It alters the signatures of some functions to have
73// constexpr qualifier and forces the use of constexpr-compatible
74// implementation, which might be a completely different code path or
75// instructions. Some of these functions exploit platform-specific non-constexpr
76// implementations to achieve certain goals, thus it is disabled by default.
77#ifndef LIBC_ENABLE_CONSTEXPR
78#define LIBC_ENABLE_CONSTEXPR 0
79#endif
80
81#endif // LLVM_LIBC_SRC___SUPPORT_MACROS_CONFIG_H
82