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Add std::is_constant_evaluated.

Browse Source 
Clang recently added __builtin_is_constant_evaluated() and GCC 9.0
has it as well.

This patch adds support for it in libc++.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@359119 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eric Fiselier 2019-04-24 17:54:25 +00:00
parent ef08906314
commit 250205c9d2
10 changed files with 103 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
docs/FeatureTestMacroTable.rst
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@ -188,7 +188,7 @@ Status
------------------------------------------------- -----------------
``__cpp_lib_generic_unordered_lookup`` *unimplemented*
------------------------------------------------- -----------------
``__cpp_lib_is_constant_evaluated`` *unimplemented*
``__cpp_lib_is_constant_evaluated`` ``201811L``
------------------------------------------------- -----------------
``__cpp_lib_list_remove_return_type`` *unimplemented*
------------------------------------------------- -----------------

4
include/__config
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@ -1257,6 +1257,10 @@ _LIBCPP_FUNC_VIS extern "C" void __sanitizer_annotate_contiguous_container(
#define _LIBCPP_HAS_NO_BUILTIN_ADDRESSOF
#endif
#if !__has_builtin(__builtin_is_constant_evaluated) && _GNUC_VER < 900
#define _LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED
#endif
#if !defined(_LIBCPP_HAS_NO_OFF_T_FUNCTIONS)
# if defined(_LIBCPP_MSVCRT) || defined(_NEWLIB_VERSION)
# define _LIBCPP_HAS_NO_OFF_T_FUNCTIONS

7
include/type_traits
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@ -4876,6 +4876,13 @@ enum class endian
};
#endif
#if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
_LIBCPP_INLINE_VISIBILITY
inline constexpr bool is_constant_evaluated() noexcept {
return __builtin_is_constant_evaluated();
}
#endif
_LIBCPP_END_NAMESPACE_STD
#if _LIBCPP_STD_VER > 14

4
include/version
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@ -222,7 +222,9 @@ __cpp_lib_void_t 201411L <type_traits>
// # define __cpp_lib_destroying_delete 201806L
# define __cpp_lib_erase_if 201811L
// # define __cpp_lib_generic_unordered_lookup 201811L
// # define __cpp_lib_is_constant_evaluated 201811L
# if !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
# define __cpp_lib_is_constant_evaluated 201811L
# endif
// # define __cpp_lib_list_remove_return_type 201806L
// # define __cpp_lib_ranges 201811L
// # define __cpp_lib_three_way_comparison 201711L

6
test/std/language.support/support.limits/support.limits.general/type_traits.version.pass.cpp
View File

@ -315,16 +315,16 @@
# endif
# endif
# if !defined(_LIBCPP_VERSION)
# if TEST_HAS_BUILTIN(__builtin_is_constant_evaluated) || TEST_GCC_VER >= 900
# ifndef __cpp_lib_is_constant_evaluated
# error "__cpp_lib_is_constant_evaluated should be defined in c++2a"
# endif
# if __cpp_lib_is_constant_evaluated != 201811L
# error "__cpp_lib_is_constant_evaluated should have the value 201811L in c++2a"
# endif
# else // _LIBCPP_VERSION
# else
# ifdef __cpp_lib_is_constant_evaluated
# error "__cpp_lib_is_constant_evaluated should not be defined because it is unimplemented in libc++!"
# error "__cpp_lib_is_constant_evaluated should not be defined when TEST_HAS_BUILTIN(__builtin_is_constant_evaluated) || TEST_GCC_VER >= 900 is not defined!"
# endif
# endif

6
test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp
View File

@ -1798,16 +1798,16 @@
# endif
# endif
# if !defined(_LIBCPP_VERSION)
# if TEST_HAS_BUILTIN(__builtin_is_constant_evaluated) || TEST_GCC_VER >= 900
# ifndef __cpp_lib_is_constant_evaluated
# error "__cpp_lib_is_constant_evaluated should be defined in c++2a"
# endif
# if __cpp_lib_is_constant_evaluated != 201811L
# error "__cpp_lib_is_constant_evaluated should have the value 201811L in c++2a"
# endif
# else // _LIBCPP_VERSION
# else
# ifdef __cpp_lib_is_constant_evaluated
# error "__cpp_lib_is_constant_evaluated should not be defined because it is unimplemented in libc++!"
# error "__cpp_lib_is_constant_evaluated should not be defined when TEST_HAS_BUILTIN(__builtin_is_constant_evaluated) || TEST_GCC_VER >= 900 is not defined!"
# endif
# endif

29
test/std/utilities/meta/meta.const.eval/is_constant_evaluated.fail.cpp Normal file
View File

@ -0,0 +1,29 @@
//===----------------------------------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
// UNSUPPORTED: c++98, c++03
// <type_traits>
#include <type_traits>
#include <cassert>
#include "test_macros.h"
int main(int, char**)
{
#ifndef __cpp_lib_is_constant_evaluated
// expected-error@+1 {{no member named 'is_constant_evaluated' in namespace 'std'}}
bool b = std::is_constant_evaluated();
#else
// expected-error@+1 {{static_assert failed}}
static_assert(!std::is_constant_evaluated(), "");
#endif
return 0;
}

50
test/std/utilities/meta/meta.const.eval/is_constant_evaluated.pass.cpp Normal file
View File

@ -0,0 +1,50 @@
//===----------------------------------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
// <type_traits>
// constexpr bool is_constant_evaluated() noexcept; // C++20
#include <type_traits>
#include <cassert>
#include "test_macros.h"
#ifndef __cpp_lib_is_constant_evaluated
#if TEST_HAS_BUILTIN(__builtin_is_constant_evaluated)
# error __cpp_lib_is_constant_evaluated should be defined
#endif
#endif
template <bool> struct InTemplate {};
int main(int, char**)
{
#ifdef __cpp_lib_is_constant_evaluated
// Test the signature
{
ASSERT_SAME_TYPE(decltype(std::is_constant_evaluated()), bool);
ASSERT_NOEXCEPT(std::is_constant_evaluated());
constexpr bool p = std::is_constant_evaluated();
assert(p);
}
// Test the return value of the builtin for basic sanity only. It's the
// compilers job to test tho builtin for correctness.
{
static_assert(std::is_constant_evaluated(), "");
bool p = std::is_constant_evaluated();
assert(!p);
ASSERT_SAME_TYPE(InTemplate<std::is_constant_evaluated()>, InTemplate<true>);
static int local_static = std::is_constant_evaluated() ? 42 : -1;
assert(local_static == 42);
}
#endif
return 0;
}

3
utils/generate_feature_test_macro_components.py
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@ -525,7 +525,8 @@ feature_test_macros = sorted([ add_version_header(x) for x in [
"c++2a": 201811L,
},
"headers": ["type_traits"],
"unimplemented": True,
"depends": "TEST_HAS_BUILTIN(__builtin_is_constant_evaluated) || TEST_GCC_VER >= 900",
"internal_depends": "!defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)",
},
{"name": "__cpp_lib_list_remove_return_type",
"values": {

2
www/cxx2a_status.html
View File

@ -113,7 +113,7 @@
<tr><td><a href="https://wg21.link/P0482R6">P0482R6</a></td><td>CWG</td><td>char8_t: A type for UTF-8 characters and strings</td><td>San Diego</td><td><i> </i></td><td></td></tr>
<tr><td><a href="https://wg21.link/P0487R1">P0487R1</a></td><td>LWG</td><td>Fixing operator&gt;&gt;(basic_istream&amp;, CharT*) (LWG 2499)</td><td>San Diego</td><td>Complete</td><td>8.0</td></tr>
<tr><td><a href="https://wg21.link/P0591R4">P0591R4</a></td><td>LWG</td><td>Utility functions to implement uses-allocator construction</td><td>San Diego</td><td><i> </i></td><td></td></tr>
<tr><td><a href="https://wg21.link/P0595R2">P0595R2</a></td><td>CWG</td><td>P0595R2 std::is_constant_evaluated()</td><td>San Diego</td><td><i> </i></td><td></td></tr>
<tr><td><a href="https://wg21.link/P0595R2">P0595R2</a></td><td>CWG</td><td>P0595R2 std::is_constant_evaluated()</td><td>San Diego</td><td>Complete</td><td>9.0</td></tr>
<tr><td><a href="https://wg21.link/P0602R4">P0602R4</a></td><td>LWG</td><td>variant and optional should propagate copy/move triviality</td><td>San Diego</td><td>Complete</td><td>8.0</td></tr>
<tr><td><a href="https://wg21.link/P0608R3">P0608R3</a></td><td>LWG</td><td>A sane variant converting constructor</td><td>San Diego</td><td><i> </i></td><td></td></tr>
<tr><td><a href="https://wg21.link/P0655R1">P0655R1</a></td><td>LWG</td><td>visit&lt;R&gt;: Explicit Return Type for visit</td><td>San Diego</td><td><i> </i></td><td></td></tr>