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From: "guihaoc at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/111449] New: memcmp (p,q,16) == 0 can be optimized
 better on ppc64 with vector comparison instructions
Date: Mon, 18 Sep 2023 02:37:19 +0000
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X-Bugzilla-Component: target
X-Bugzilla-Version: 13.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111449

            Bug ID: 111449
           Summary: memcmp (p,q,16) =3D=3D 0 can be optimized better on ppc=
64
                    with vector comparison instructions
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: guihaoc at gcc dot gnu.org
  Target Milestone: ---

int compare (const char* s1, const char* s2)
{
  return __builtin_memcmp (s1, s2, 16) =3D=3D 0;
}


trunk outputs
        ld 10,0(3)
        ld 9,0(4)
        cmpd 0,10,9
        beq 0,.L6
.L2:
        li 3,1
        cntlzw 3,3
        srwi 3,3,5
        blr
        .p2align 4,,15
.L6:
        ld 10,8(3)
        ld 9,8(4)
        li 3,0
        cmpd 0,10,9
        bne 0,.L2
        cntlzw 3,3
        srwi 3,3,5
        blr

Expect to use vector comparison to eliminate branches.
        lxv 32,0(3)
        lxv 33,0(4)
        vcmpequb. 0,0,1
        mfcr 3,2
        rlwinm 3,3,25,1
        blr=