https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96851
Bug ID: 96851
Summary: operator< on std::array<T, N> does not work in
constexpr, for sizeof(T) == 1, and N > 1
Product: gcc
Version: 10.1.0
URL: https://gcc.godbolt.org/z/vjvYE5
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: milasudril at gmail dot com
Target Milestone: ---
It appears that `operator<` on `std::array<T, N>` does not work in constexpr
context, for `sizeof(T) == 1`, and `N > 1`. I tried different `T`and `N`
combinations, and it appears that these work.
MWE:
#include <array>
#include <cstddef>
#include <cstdint>
template<class T, size_t N>
constexpr bool test(std::array<T, N> const& a, std::array<T, N> const& b)
{
return a < b;
}
using Type = int8_t;
constexpr auto Count = 2;
// Below does not compile
constexpr auto value = test(std::array<Type, Count>{}, std::array<Type,
Count>{});
The problem exists in gcc 10.1 and trunk.
/opt/compiler-explorer/gcc-trunk-20200830/include/c++/11.0.0/array:262:32:
error: '__builtin_memcmp(((std::array<signed char,
2>::const_pointer)(&<anonymous>.std::array<signed char, 2>::_M_elems)),
((std::array<signed char, 2>::const_pointer)(&<anonymous>.std::array<signed
char, 2>::_M_elems)), 2)' is not a constant expression
262 | return __builtin_memcmp(__a.data(), __b.data(), _Nm) <=> 0;
Godbolt url: https://gcc.godbolt.org/z/vjvYE5
