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From: "antoshkka at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/110457] New: Unnecessary movsx   eax, dil
Date: Wed, 28 Jun 2023 15:05:52 +0000
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X-Bugzilla-Keywords: missed-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110457

            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=