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Add a private call '__libcpp_is_constant_evaluated' which 'works' for old language versions and w/o any compiler support. 'Working', in this case, means that it returns false in those cases.

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git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@364873 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Marshall Clow 2019-07-01 23:16:46 +00:00
parent 268aced50d
commit e380104a43
2 changed files with 40 additions and 1 deletions
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7
include/type_traits
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@ -3999,13 +3999,18 @@ enum class endian
};
#endif
#if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
#ifndef _LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED
#if _LIBCPP_STD_VER > 17
_LIBCPP_INLINE_VISIBILITY
inline constexpr bool is_constant_evaluated() noexcept {
return __builtin_is_constant_evaluated();
}
#endif
_LIBCPP_CONSTEXPR bool __libcpp_is_constant_evaluated() _NOEXCEPT { return __builtin_is_constant_evaluated(); }
#else
_LIBCPP_CONSTEXPR bool __libcpp_is_constant_evaluated() _NOEXCEPT { return false; }
#endif
template <class _CharT>
using _IsCharLikeType = _And<is_standard_layout<_CharT>, is_trivial<_CharT> >;

34
test/libcxx/type_traits/is_constant_evaluated.pass.cpp Normal file
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@ -0,0 +1,34 @@
//===----------------------------------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// <type_traits>
// __libcpp_is_constant_evaluated()
// returns false when there's no constant evaluation support from the compiler.
// as well as when called not in a constexpr context
#include <type_traits>
#include <cassert>
#include "test_macros.h"
int main (int, char**) {
ASSERT_SAME_TYPE(decltype(std::__libcpp_is_constant_evaluated()), bool);
ASSERT_NOEXCEPT(std::__libcpp_is_constant_evaluated());
#if !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED) && !defined(_LIBCPP_CXX03_LANG)
static_assert(std::__libcpp_is_constant_evaluated(), "");
#endif
bool p = std::__libcpp_is_constant_evaluated();
assert(!p);
return 0;
}