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From: "tkoenig at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/110479] New: Unnecessary register move
Date: Thu, 29 Jun 2023 08:03:18 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110479

            Bug ID: 110479
           Summary: Unnecessary register move
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tkoenig at gcc dot gnu.org
  Target Milestone: ---

May be related to / a dup of PR110240.

The function

unsigned int bar(unsigned int a)
{
  return 1u << (((a >> 10) & 3) + 3);
}

is compiled, with a relatively recent trunk and -O3, to

bar:
.LFB12:
        .cfi_startproc
        shrl    $10, %edi
        movl    $1, %eax
        movl    %edi, %ecx
        andl    $3, %ecx
        addl    $3, %ecx
        sall    %cl, %eax
        ret

where the register move seems unnecessary.=