[Bug target/109406] New: Missing use of aarch64 SVE2 unpredicated integer multiply

[ktkachov at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109406

            Bug ID: 109406
           Summary: Missing use of aarch64 SVE2 unpredicated integer
                    multiply
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ktkachov at gcc dot gnu.org
  Target Milestone: ---
            Target: aarch64

For the testcase
#define N 1024

long long res[N];
long long in1[N];
long long in2[N];

void
mult (void)
{
  for (int i = 0; i < N; i++)
    res[i] = in1[i] * in2[i];
}

With -O3 -march=armv8.5-a+sve2 we generate the loop:
        ptrue   p1.b, all
        whilelo p0.d, wzr, w2
.L2:
        ld1d    z0.d, p0/z, [x4, x0, lsl 3]
        ld1d    z1.d, p0/z, [x3, x0, lsl 3]
        mul     z0.d, p1/m, z0.d, z1.d
        st1d    z0.d, p0, [x1, x0, lsl 3]
        incd    x0
        whilelo p0.d, w0, w2
        b.any   .L2
        ret

SVE2 supports the MUL (vectors, unpredicated) instruction that would allow us
to  eliminate the use of p1. Clang manages to do this (though it has other
inefficiencies) in https://godbolt.org/z/7xj6xEchx