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From: "pan2.li at intel dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/113697] New: RISC-V: Redundant vsetvl insn in function
Date: Thu, 01 Feb 2024 01:59:35 +0000
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X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113697

            Bug ID: 113697
           Summary: RISC-V: Redundant vsetvl insn in function
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pan2.li at intel dot com
  Target Milestone: ---

Give the sample code as below, build with -march=3Drv64gcv -O3 -g0

int foo (int * __restrict a, int n)
{
    int result =3D 0;
    for (int i =3D 0; i < n; i++)
      result +=3D a[i];
    return result;
}

The asm code looks like below, we have one duplicated vsetvl insn here.

foo:
.LFB0:
        .cfi_startproc
        ble     a1,zero,.L4
        vsetvli a5,zero,e32,m1,ta,ma
        vmv.v.i v1,0
.L3:
        vsetvli a5,a1,e32,m1,tu,ma
        slli    a4,a5,2
        sub     a1,a1,a5
        vle32.v v2,0(a0)
        add     a0,a0,a4
        vadd.vv v1,v2,v1
        bne     a1,zero,.L3
        li      a5,0
        vsetivli        zero,1,e32,m1,ta,ma
        vmv.s.x v2,a5
        vsetvli a5,zero,e32,m1,ta,ma  <=3D=3D redundant vsetvl
        vredsum.vs      v1,v1,v2
        vmv.x.s a0,v1
        ret
.L4:
        li      a0,0
        ret=