[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 #22 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Jakub Jelinek from comment #21)
> Created attachment 42660 [details]
> gcc8-pr78821-i386.patch
> 
> Untested patch for the -mmovbe movbew loads/stores.  Note, is there any
> particular reason why we don't use for AT&T syntax w/l/q suffixes for movbe?
> At least looking at binutils testsuite, it covers both movbe without suffix
> and movbe[wlq].  On the other side, for bswap insn there are no suffixes.

No particular reason - we should add suffixes.

OTOH, proposed patch should use enabled attribute to enable xchg, and split the
pattern after reload to lose FLAGS_REG clobber for xchg and movbe
aliternatives.