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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/110485] New: vectorizing simd clone calls
 without loop masking applied
Date: Thu, 29 Jun 2023 12:21:21 +0000
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X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110485

            Bug ID: 110485
           Summary: vectorizing simd clone calls without loop masking
                    applied
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

#include <math.h>

double a[1024];
double b[1024];

void foo (int n)
{
  for (int i =3D 0; i < n; ++i)
    a[i] =3D pow (b[i], 71.2);
}

with -Ofast -march=3Dznver4 --param vect-partial-vector-usage=3D1 gets us
the following OK main loop

.L4:
        vmovapd b(%rbx), %zmm0
        vmovapd -112(%rbp), %zmm1
        addq    $64, %rbx
        call    _ZGVeN8vv_pow
        vmovapd %zmm0, a-64(%rbx)
        cmpq    %r13, %rbx
        jne     .L4

but the following vectorized masked epilogue:

        movl    %r12d, %eax
        andl    $-8, %eax
        testb   $7, %r12b
        je      .L13
.L3:
        subl    %eax, %r12d
        movl    %eax, %edx
        vmovapd -112(%rbp), %zmm1
        vpbroadcastw    %r12d, %xmm0
        leaq    0(,%rdx,8), %rbx
        vpcmpuw $6, .LC2(%rip), %xmm0, %k1
        vmovapd b(,%rdx,8), %zmm0{%k1}{z}
        kmovb   %k1, -113(%rbp)
        call    _ZGVeN8vv_pow
        kmovb   -113(%rbp), %k1
        vmovapd %zmm0, a(%rbx){%k1}

so we simply call _ZGVeN8vv_pow without any masking applied.  That's
possibly OK since we use zero-masking and thus actual masked argument
lanes are zero but it seems this isn't the expected behavior for
vectorizable_simd_clone_call.  Instead it should probably unconditionally
set LOOP_VINFO_CAN_USE_PARTIAL_VECTORS_P (loop_vinfo) to false?

Is there a way to query which SIMD clone is "happy" with zero arguments
and thus for example with -ffast-math would be OK to run unmasked?=