[Bug target/101579] Suboptimal codegen for __builtin_shufflevector

[crazylht at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101579

--- Comment #8 from Hongtao.liu <crazylht at gmail dot com> ---
> 
>   U u = ((union { V a; U b; }) w).b + ((union { V a; U b; }) w).b[1];
>   return u;
> 
> I means the result u only cared about the first half, we can drop the second
> half, it's redundant.

Sorry for the typo, just want to clarify

result u = ((union { V a; U b; }) w).b + ((union { V a; U b; }) w).b[1]

where "(union { V a; U b; }) w).b" only cares about the first half, so does
"((union { V a; U b; }) w).b[1]" and "u", the second half of v is never used
and can be optimized away.