[Bug target/110457] New: Unnecessary movsx eax, dil

[antoshkka at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110457

            Bug ID: 110457
           Summary: Unnecessary movsx   eax, dil
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: antoshkka at gmail dot com
  Target Milestone: ---

For the following code

int sample1(char c) {
  return (c << 4) + (c << 8) + (c << 16) + c;
}


GCC-14 with -O2 generates the assembly:

sample1(char):
 movsx  eax,dil
 imul   eax,eax,0x10111
 ret


However, it could be shortened to just:

sample1(char):
 imul   eax,edi,0x10111


Godbolt playground: https://godbolt.org/z/7GGdedEY8