https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103887
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Michal Kubecek from comment #2)
> (In reply to Andrew Pinski from comment #1)
> > The problem is rather __builtin_constant_p not resolving to a constant. This
> > is a dup of bug 79482.
>
> There is a difference: your modified testcase fails to compile regardless of
> -fsanitize=shift while mine fails only with this option and succeeds without
> it. If __builtin_constant_p(tr) not being handled as constant were the
> problem,
> the result should not depend on presence of "-fsanitize=shift".
Right, but the problem is __builtin_constant_p is not resolved to 0 forcing
what is inside the static_assert to be non-constant in both cases.
Even take a look at this:
#include <stdint.h>
#define ASSERT_ON_COMPILE_SELECTOR_SIZE(e) \
_Static_assert(((__builtin_constant_p(e) && ((e) >> 16) == 0)) || \
(sizeof(e) <= 2), "problem")
int f(uint32_t tr)
{
ASSERT_ON_COMPILE_SELECTOR_SIZE(tr);
return 0;
}
The static assert fails but fails because the expression is non-constant at -O2
and above. This is similar to your original case except without using
-fsanitize=shift even.
