gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated2.C

   1 // P0595R1
   2 // { dg-do run { target c++14 } }
   3
   4 constexpr inline bool
   5 is_constant_evaluated () noexcept
   6 {
   7   return __builtin_is_constant_evaluated ();
   8 }
   9
  10 template<int N> struct X { int v = N; };
  11 X<is_constant_evaluated ()> x; // type X<true>
  12 int y = 4;
  13 int a = is_constant_evaluated () ? y : 1; // initializes a to 1
  14 int b = is_constant_evaluated () ? 2 : y; // initializes b to 2
  15 int c = y + (is_constant_evaluated () ? 2 : y); // initializes c to 2*y
  16 int d = is_constant_evaluated (); // initializes d to 1
  17 int e = d + is_constant_evaluated (); // initializes e to 1 + 0
  18
  19 struct false_type { static constexpr bool value = false; };
  20 struct true_type { static constexpr bool value = true; };
  21 template<class T, class U>
  22 struct is_same : false_type {};
  23 template<class T>
  24 struct is_same<T, T> : true_type {};
  25
  26 constexpr int
  27 foo (int x)
  28 {
  29   const int n = is_constant_evaluated () ? 13 : 17; // n == 13
  30   int m = is_constant_evaluated () ? 13 : 17; // m might be 13 or 17 (see below)
  31   char arr[n] = {}; // char[13]
  32   return m + sizeof (arr) + x;
  33 }
  34
  35 constexpr int
  36 bar ()
  37 {
  38   const int n = is_constant_evaluated() ? 13 : 17;
  39   X<n> x1;
  40   X<is_constant_evaluated() ? 13 : 17> x2;
  41   static_assert (is_same<decltype (x1), decltype (x2)>::value, "x1/x2's type");
  42   return x1.v + x2.v;
  43 }
  44
  45 int p = foo (0); // m == 13; initialized to 26
  46 int q = p + foo (0); // m == 17 for this call; initialized to 56
  47 static_assert (bar () == 26, "bar");
  48
  49 struct S { int a, b; };
  50
  51 S s = { is_constant_evaluated () ? 2 : 3, y };
  52 S t = { is_constant_evaluated () ? 2 : 3, 4 };
  53
  54 static_assert (is_same<decltype (x), X<true> >::value, "x's type");
  55
  56 int
  57 main ()
  58 {
  59   if (a != 1 || b != 2 || c != 8 || d != 1 || e != 1 || p != 26 || q != 56)
  60     __builtin_abort ();
  61   if (s.a != 3 || s.b != 4 || t.a != 2 || t.b != 4)
  62     __builtin_abort ();
  63   if (foo (y) != 34)
  64     __builtin_abort ();
  65 #if __cplusplus >= 201703L
  66   if constexpr (foo (0) != 26)
  67     __builtin_abort ();
  68 #endif
  69   constexpr int w = foo (0);
  70   if (w != 26)
  71     __builtin_abort ();
  72 }