https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66299
--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I'd think using a volatile var in the optimization test is highly undesirable,
that can mean stopping optimizations differently between different compilers.
But, the same thing can be reproduced with:
void
foo (signed int x)
{
unsigned int t = ((unsigned int) 1U << x);
if (t != 2U)
__builtin_abort ();
}
Perhaps we should have a match.pd simplification of (const1 << var) {==,!=}
const2, perhaps something even for {<,<=,>,>=} if they could be simplified to a
simple comparison of var and const3; supposedly guarded with single use of the
shift. What about >> ? Other arithmetics single use operations (e.g. 2U * var
== 16)? For addition of a constant apparently forwprop1 already optimizes
that.
