https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108199
--- Comment #3 from Andreas Krebbel <krebbel at gcc dot gnu.org> ---
Moving the local definition of dst out of the function to global scope prevents
the store from getting eliminated.
union DST dst;
As expected the store is still in the FRE dump:
_1 = src_6(D)->a;
dst.val = _1; <---
_2 = BIT_FIELD_REF <dst, 8, 0>;
_3 = _2 & 64;
if (_3 != 0)
...
and the first by is accessed:
bar:
movq (%rdi), %rax
movq %rax, dst(%rip)
testb $64, %al
jne .L11
