[Bug ipa/65478] [5 regression] crafty performance regression

["hubicka at ucw dot cz" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65478

--- Comment #17 from Jan Hubicka <hubicka at ucw dot cz> ---
>   <bb 2>:
>   x.d = arg1_3(D);
>   _5 = x.i[3];
>   if (_5 != 0)
>     goto <bb 3>;
>   else
>     goto <bb 4>;
> ...
>   <bb 4>:
>   _12 = x.i[2];
>   if (_12 != 0)
>     goto <bb 5>;
>   else
>     goto <bb 6>;
> 
> to sth like
> 
>   <bb 4>:
>   _12 = (unsigned short)(arg1_3(D) >> 32);
>   if (_12 != 0)
>     goto <bb 5>;
>   else
>     goto <bb 6>;
> 
> ?
> 
> SCCVN doesn't handle sth "fancy" for the case of union accesses with
> not matching offset/size.  We could add that, but I suppose in your
> case it's just for the sake of inliner predicates as the actual generated
> code might be worse on some targets?

Currently function have 1 store and 8 loads, with the change, it would have
4 loads that would make it cheaper (and would make predicates work indeed).
> 
>   _12 = BIT_FIELD_REF <arg1_3(D), ...>
> 
> (or REALPART/IMAGPART for special cases where that is valid).

Yeah, that would be nice!