Filed as PR63401: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63401
> This is easy to see with a simple C test case:
>
> //__attribute__ ((optimize("strength-reduce")))
> int foo (float x) { return __builtin_isnan(x); }
>
> Compiled with -O3 -ffast-math, the isnan is simplified out (fast math means
> no NaNs). If you uncomment the attribute (chosen because it’s actually
> useless), and compile again with -O3 -ffast-math: the isnan test is not
> simplified any more. This is because the codepath through
> default_options_optimization() has overwritten the value of the flags handled
> in set_fast_math_flags(): flag_finite_math_only, flag_signed_zeros,
> flag_trapping_math and flag_unsafe_math_optimizations.
>
> I’m CC’ing the maintainers who added the optimize attribute in the first
> place, as they might have an idea how to fix this. This is way beyond my
> league!
>
>
> Thanks Steven for your help!
> FX
