[Bug middle-end/124453] suboptimal read of 64-bit bitfields

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124453

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #1)
> #ifdef dd
>     auto t = val.b;
>     if(t == 0)
> #else
>     if (val.b == 0)
> #endif
> 
> The problem is too early `optimizing` of val.b == 0.

To

  if ((BIT_FIELD_REF <val, 8, 0> & 30) == 0)

by famous premature fold-const.cc code.