[Bug target/85730] complex code for modifying lowest byte in a 4-byte vector

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85730

--- Comment #8 from Uroš Bizjak <ubizjak at gmail dot com> ---
Created attachment 51564
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51564&action=edit
Prototype patch

Attached patch works around reload problem and creates:

        movl    %edi, %eax
        movb    %dil, %al
        addb    %al, %al
        ret

for all cases. Please note that some follow-up pass is needed to remove
"movb %dil, %al", since preceding instruction already moves full value from
%edi to %eax, so partial move is not needed.