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// Workaround for compilers that do not support builtin detection.
17// FIXME: This is only required for the GPU portion which should be moved.
18#ifndef __has_builtin
19#define __has_builtin(b) 0
20#endif
21
22// Compiler feature-detection.
23// clang.llvm.org/docs/LanguageExtensions.html#has-feature-and-has-extension
24#ifdef __has_feature
25#define LIBC_HAS_FEATURE(f) __has_feature(f)
26#else
27#define LIBC_HAS_FEATURE(f) 0
28#endif
29
30#ifdef __clang__
31// Declare a LIBC_NAMESPACE with hidden visibility. `namespace
32// LIBC_NAMESPACE_DECL {` should be used around all declarations and definitions
33// for libc internals as opposed to just `namespace LIBC_NAMESPACE {`. This
34// ensures that all declarations within this namespace have hidden
35// visibility, which optimizes codegen for uses of symbols defined in other
36// translation units in ways that can be necessary for correctness by avoiding
37// dynamic relocations. This does not affect the public C symbols which are
38// controlled independently via `LLVM_LIBC_FUNCTION_ATTR`.
39#define LIBC_NAMESPACE_DECL [[gnu::visibility("hidden")]] LIBC_NAMESPACE
40#else
41// TODO(#98548): GCC emits a warning when using the visibility attribute which
42// needs to be diagnosed and addressed.
43#define LIBC_NAMESPACE_DECL LIBC_NAMESPACE
44#endif
45
46#endif // LLVM_LIBC_SRC___SUPPORT_MACROS_CONFIG_H
47