Viewing file:  is-constant-evaluated2.C (1.96 KB) -rw-r--r--
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// P0595R1
// { dg-do run { target c++14 } }
constexpr inline bool
is_constant_evaluated () noexcept
{
return __builtin_is_constant_evaluated ();
}
template<int N> struct X { int v = N; };
X<is_constant_evaluated ()> x; // type X<true>
int y = 4;
int a = is_constant_evaluated () ? y : 1; // initializes a to 1
int b = is_constant_evaluated () ? 2 : y; // initializes b to 2
int c = y + (is_constant_evaluated () ? 2 : y); // initializes c to 2*y
int d = is_constant_evaluated (); // initializes d to 1
int e = d + is_constant_evaluated (); // initializes e to 1 + 0
struct false_type { static constexpr bool value = false; };
struct true_type { static constexpr bool value = true; };
template<class T, class U>
struct is_same : false_type {};
template<class T>
struct is_same<T, T> : true_type {};
constexpr int
foo (int x)
{
const int n = is_constant_evaluated () ? 13 : 17; // n == 13
int m = is_constant_evaluated () ? 13 : 17; // m might be 13 or 17 (see below)
char arr[n] = {}; // char[13]
return m + sizeof (arr) + x;
}
constexpr int
bar ()
{
const int n = is_constant_evaluated() ? 13 : 17;
X<n> x1;
X<is_constant_evaluated() ? 13 : 17> x2;
static_assert (is_same<decltype (x1), decltype (x2)>::value, "x1/x2's type");
return x1.v + x2.v;
}
int p = foo (0); // m == 13; initialized to 26
int q = p + foo (0); // m == 17 for this call; initialized to 56
static_assert (bar () == 26, "bar");
struct S { int a, b; };
S s = { is_constant_evaluated () ? 2 : 3, y };
S t = { is_constant_evaluated () ? 2 : 3, 4 };
static_assert (is_same<decltype (x), X<true> >::value, "x's type");
int
main ()
{
if (a != 1 || b != 2 || c != 8 || d != 1 || e != 1 || p != 26 || q != 56)
__builtin_abort ();
if (s.a != 3 || s.b != 4 || t.a != 2 || t.b != 4)
__builtin_abort ();
if (foo (y) != 34)
__builtin_abort ();
#if __cplusplus >= 201703L
if constexpr (foo (0) != 26)
__builtin_abort ();
#endif
constexpr int w = foo (0);
if (w != 26)
__builtin_abort ();
}
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