src/__support/common.h

//===-- Common internal contructs -------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_LIBC_SUPPORT_COMMON_H
#define LLVM_LIBC_SUPPORT_COMMON_H

#include "src/__support/macros/attributes.h"
#include "src/__support/macros/properties/architectures.h"

#ifndef LLVM_LIBC_FUNCTION_ATTR
#define LLVM_LIBC_FUNCTION_ATTR
#endif

// GPU targets do not support aliasing.
#if defined(LIBC_COPT_PUBLIC_PACKAGING) && defined(LIBC_TARGET_ARCH_IS_GPU)
#define LLVM_LIBC_FUNCTION_IMPL(type, name, arglist)                           \
  LLVM_LIBC_FUNCTION_ATTR decltype(__llvm_libc::name)                          \
      __##name##_impl__ __asm__(#name);                                        \
  type __##name##_impl__ arglist
// MacOS needs to be excluded because it does not support aliasing.
#elif defined(LIBC_COPT_PUBLIC_PACKAGING) && (!defined(__APPLE__))
#define LLVM_LIBC_FUNCTION_IMPL(type, name, arglist)                           \
  LLVM_LIBC_FUNCTION_ATTR decltype(__llvm_libc::name)                          \
      __##name##_impl__ __asm__(#name);                                        \
  decltype(__llvm_libc::name) name [[gnu::alias(#name)]];                      \
  type __##name##_impl__ arglist
#else
#define LLVM_LIBC_FUNCTION_IMPL(type, name, arglist) type name arglist
#endif

// This extra layer of macro allows `name` to be a macro to rename a function.
#define LLVM_LIBC_FUNCTION(type, name, arglist)                                \
  LLVM_LIBC_FUNCTION_IMPL(type, name, arglist)

namespace __llvm_libc {
namespace internal {
constexpr bool same_string(char const *lhs, char const *rhs) {
  for (; *lhs || *rhs; ++lhs, ++rhs)
    if (*lhs != *rhs)
      return false;
  return true;
}
} // namespace internal
} // namespace __llvm_libc

// LLVM_LIBC_IS_DEFINED checks whether a particular macro is defined.
// Usage: constexpr bool kUseAvx = LLVM_LIBC_IS_DEFINED(__AVX__);
//
// This works by comparing the stringified version of the macro with and without
// evaluation. If FOO is not undefined both stringifications yield "FOO". If FOO
// is defined, one stringification yields "FOO" while the other yields its
// stringified value "1".
#define LLVM_LIBC_IS_DEFINED(macro)                                            \
  !__llvm_libc::internal::same_string(                                         \
      LLVM_LIBC_IS_DEFINED__EVAL_AND_STRINGIZE(macro), #macro)
#define LLVM_LIBC_IS_DEFINED__EVAL_AND_STRINGIZE(s) #s

#endif // LLVM_LIBC_SUPPORT_COMMON_H