libcxx/test/std/utilities/meta/meta.const.eval/is_constant_evaluated.pass.cpp

   1 //===----------------------------------------------------------------------===//
   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
   9 // UNSUPPORTED: c++03, c++11, c++14, c++17
  10
  11 // <type_traits>
  12
  13 // constexpr bool is_constant_evaluated() noexcept; // C++20
  14
  15 #include <type_traits>
  16 #include <cassert>
  17
  18 #include "test_macros.h"
  19
  20 #ifndef __cpp_lib_is_constant_evaluated
  21 #if TEST_HAS_BUILTIN(__builtin_is_constant_evaluated)
  22 # error __cpp_lib_is_constant_evaluated should be defined
  23 #endif
  24 #endif
  25
  26 // Disable the tautological constant evaluation warnings for this test,
  27 // because it's explicitly testing those cases.
  28 TEST_CLANG_DIAGNOSTIC_IGNORED("-Wconstant-evaluated")
  29 TEST_MSVC_DIAGNOSTIC_IGNORED(5063)
  30
  31 template <bool> struct InTemplate {};
  32
  33 int main(int, char**)
  34 {
  35   // Test the signature
  36   {
  37     ASSERT_SAME_TYPE(decltype(std::is_constant_evaluated()), bool);
  38     ASSERT_NOEXCEPT(std::is_constant_evaluated());
  39     constexpr bool p = std::is_constant_evaluated();
  40     assert(p);
  41   }
  42   // Test the return value of the builtin for basic sanity only. It's the
  43   // compiler's job to test the builtin for correctness.
  44   {
  45     static_assert(std::is_constant_evaluated(), "");
  46     bool p = std::is_constant_evaluated();
  47     assert(!p);
  48     ASSERT_SAME_TYPE(InTemplate<std::is_constant_evaluated()>, InTemplate<true>);
  49     static int local_static = std::is_constant_evaluated() ? 42 : -1;
  50     assert(local_static == 42);
  51   }
  52   return 0;
  53 }