[Bug c++/88445] New: noexcept(expr) should return true with -fno-exceptions

[antoshkka at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88445

            Bug ID: 88445
           Summary: noexcept(expr) should return true with -fno-exceptions
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: antoshkka at gmail dot com
  Target Milestone: ---

Consider the following example:

#include <type_traits>

struct test {
    test();
    test(test&&);
    test& operator=(test&&);
};

void test_func() {
    static_assert(noexcept(test{test()}), "");
    static_assert(std::is_nothrow_move_constructible<test>::value, "");
    static_assert(std::is_nothrow_move_assignable<test>::value, "");
}


The static assertions fail with the -fno-exceptions flag however no exception
could happen because all the exceptions are disabled.

Please adjust the noexcept(expr) logic for the -fno-exceptions flag.

Such adjustment is essential because the standard library heavily relies on the
type traits and chooses the suboptimal algorithms in -fno-exceptions
environments.