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From: "crazylht at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/109038] New: Miss optimization to simplify bit_and +
 rotate to shift
Date: Mon, 06 Mar 2023 09:55:49 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: middle-end
X-Bugzilla-Version: 13.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109038

            Bug ID: 109038
           Summary: Miss optimization to simplify bit_and + rotate to
                    shift
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: crazylht at gmail dot com
  Target Milestone: ---
            Target: x86_64-*-* i?86-*-*

unsigned
foo (unsigned int a)
{
  unsigned int b =3D a & 0x00FFFFFF;
  unsigned int c =3D ((b & 0x000000FF) << 8
                    | (b & 0x0000FF00) << 8
                    | (b & 0x00FF0000) << 8
                    | (b & 0xFF000000) >> 24);
  return c;
}

gcc generates

foo:
        mov     eax, edi
        and     eax, 16777215
        rol     eax, 8
        ret

But it can be optimized as below

foo:                                    # @foo
        mov     eax, edi
        shl     eax, 8
        ret=