libstdc++-v3/testsuite/20_util/is_constant_evaluated/1.cc

   1 // Copyright (C) 2018-2023 Free Software Foundation, Inc.
   2 //
   3 // This file is part of the GNU ISO C++ Library.  This library is free
   4 // software; you can redistribute it and/or modify it under the
   5 // terms of the GNU General Public License as published by the
   6 // Free Software Foundation; either version 3, or (at your option)
   7 // any later version.
   8
   9 // This library is distributed in the hope that it will be useful,
  10 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 // GNU General Public License for more details.
  13
  14 // You should have received a copy of the GNU General Public License along
  15 // with this library; see the file COPYING3.  If not see
  16 // <http://www.gnu.org/licenses/>.
  17
  18 // { dg-options "-std=gnu++2a" }
  19 // { dg-do run { target c++2a } }
  20
  21 #include <type_traits>
  22 #include <testsuite_hooks.h>
  23
  24 template<int N>
  25 struct X { int v = N; };
  26 X<std::is_constant_evaluated()> x; // type X<true>
  27 int y = 4;
  28 int a = std::is_constant_evaluated() ? y : 1; // initializes a to 1
  29 int b = std::is_constant_evaluated() ? 2 : y; // initializes b to 2
  30 int c = y + (std::is_constant_evaluated() ? 2 : y); // initializes c to 2*y
  31 int d = std::is_constant_evaluated(); // initializes d to 1
  32 int e = d + std::is_constant_evaluated(); // initializes e to 1 + 0
  33
  34 constexpr int
  35 foo(int x)
  36 {
  37   const int n = std::is_constant_evaluated() ? 13 : 17; // n == 13
  38   int m = std::is_constant_evaluated() ? 13 : 17; // m might be 13 or 17 (see below)
  39   char arr[n] = {}; // char[13]
  40   return m + sizeof (arr) + x;
  41 }
  42
  43 constexpr int
  44 bar()
  45 {
  46   const int n = std::is_constant_evaluated() ? 13 : 17;
  47   X<n> x1;
  48   X<std::is_constant_evaluated() ? 13 : 17> x2;
  49   static_assert(std::is_same<decltype(x1), decltype(x2)>::value,
  50                 "x1/x2's type");
  51   return x1.v + x2.v;
  52 }
  53
  54 int p = foo(0); // m == 13; initialized to 26
  55 int q = p + foo(0); // m == 17 for this call; initialized to 56
  56 static_assert(bar() == 26, "bar");
  57
  58 struct S { int a, b; };
  59
  60 S s = { std::is_constant_evaluated() ? 2 : 3, y };
  61 S t = { std::is_constant_evaluated() ? 2 : 3, 4 };
  62
  63 static_assert(std::is_same<decltype(x), X<true> >::value, "x's type");
  64
  65 void
  66 test01()
  67 {
  68   VERIFY( a == 1 && b == 2 && c == 8 && d == 1 && e == 1 && p == 26 );
  69   VERIFY( q == 56 && s.a == 3 && s.b == 4 && t.a == 2 && t.b == 4 );
  70   VERIFY( foo (y) == 34 );
  71   if constexpr (foo (0) != 26)
  72     VERIFY( 0 );
  73   constexpr int w = foo (0);
  74   VERIFY( w == 26 );
  75 }
  76
  77 int main()
  78 {
  79   test01();
  80 }