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From: "ktkachov at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/102066] New: aarch64: Suboptimal addressing modes for
 SVE LD1W, ST1W
Date: Wed, 25 Aug 2021 14:46:53 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102066

            Bug ID: 102066
           Summary: aarch64: Suboptimal addressing modes for SVE LD1W,
                    ST1W
           Product: gcc
           Version: 12.0
            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
                CC: rsandifo at gcc dot gnu.org
  Target Milestone: ---
            Target: aarch64

For the code:
#include <arm_sve.h>

void foo(int n, float *x, float *y) {
    for (unsigned i=3D0; i<n; i+=3Dsvcntw()) {
        svfloat32_t val =3D svld1_f32(svptrue_b8(), &x[i]);
        svst1_f32(svptrue_b8(), &y[i], val);
    }
}

at -O3 -march=3Darmv8.2-a+sve GCC generates:
foo:
        cbz     w0, .L1
        mov     w4, 0
        cntw    x6
        ptrue   p0.b, all
.L3:
        ubfiz   x3, x4, 2, 32
        add     w4, w4, w6
        add     x5, x1, x3
        add     x3, x2, x3
        ld1w    z0.s, p0/z, [x5]
        st1w    z0.s, p0, [x3]
        cmp     w4, w0
        bcc     .L3
.L1:
        ret

but it could be making better use of the addressing modes:
foo:                                    // @foo
        cbz     w0, .LBB0_3
        mov     w8, wzr
        ptrue   p0.b
        cntw    x9
.LBB0_2:                                // %for.body
        mov     w10, w8
        ld1w    { z0.s }, p0/z, [x1, x10, lsl #2]
        add     w8, w8, w9
        cmp     w8, w0
        st1w    { z0.s }, p0, [x2, x10, lsl #2]
        b.lo    .LBB0_2
.LBB0_3:                                // %for.cond.cleanup
        ret

I guess the predicates and constraints in @aarch64_pred_mov<mode> in
aarch64-sve.md should allow for the scaled address modes=