[Bug tree-optimization/78821] GCC7: Copying whole 32 bits structure field by field not optimised into copying whole 32 bits at once

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78821

--- Comment #8 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to rguenther@suse.de from comment #6)

> > In addition to a merge opportunity, there is a redundant move [*], that results
> > in redundant operation [**]. The whole function could be just:
> > 
> >         movw    %dx, -4(%rdi,%rsi)
> >         notl    %edx
> >         movw    %dx, -2(%rdi,%rsi)
> 
> or
> 
>           xorl    $0xffff0000, %edx
>           movl    %edx, -4(%rdi,%rsi)
> 
> ?

Yes, even this. It looks that store merging opens many optimization
opportunities.