From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id 5D72D3858CDB; Thu,  9 Mar 2023 10:21:10 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 5D72D3858CDB
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1678357270;
	bh=7RagV8ZmZJm7pZi1KyeH2p+0QhjIc59bxUZdu+NoaOY=;
	h=From:To:Subject:Date:From;
	b=rVIv3cMC4l+cXmPd/5sMSzCegBJpcouc0KbOcBvglvXLfWs4b/AzzlgSXWuQLvlka
	 mmLZjgxVdVu/OLN3kN1pzWHnbHYsLdROoXk0n6hFgaKqRIaRFSF9+jXq6dQEPJJVnY
	 z+8lx1/l1RWwAuMJ+0Qq6pC65mgOuTcNFbrLcD3c=
From: "dorazzsoft at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/109078] New: Missing optimization on aarch64 for types
 like `float32x4x2_t`
Date: Thu, 09 Mar 2023 10:21:09 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 12.2.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: dorazzsoft at gmail dot com
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter target_milestone
Message-ID: <bug-109078-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109078

            Bug ID: 109078
           Summary: Missing optimization on aarch64 for types like
                    `float32x4x2_t`
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dorazzsoft at gmail dot com
  Target Milestone: ---

Here is a simple code: https://godbolt.org/z/3qMTTfcfx

#include <arm_neon.h>
#include <stddef.h>
#include <stdbool.h>

void simple_gemm(
  float* restrict out,
  float const* restrict a,
  float const* restrict b,
  size_t k, bool zero_out
) {
  register float32x4x2_t o0;
  o0.val[0] =3D vdupq_n_f32(0.0f);
  o0.val[1] =3D vdupq_n_f32(0.0f);

  // begin dot
  {
    register float32x4_t a0;
    register float32x4x2_t b0;

    while (k >=3D 1) {
      b0 =3D vld1q_f32_x2(b);
      a0 =3D vdupq_n_f32(a[0]);

      o0.val[0] =3D vfmaq_f32(o0.val[0], a0, b0.val[0]);
      o0.val[1] =3D vfmaq_f32(o0.val[1], a0, b0.val[1]);

      b +=3D 8;
      a +=3D 1;
      k -=3D 1;
    }
  } // end dot

  // begin writeback
  {
    if (!zero_out) {
      register float32x4x2_t t0;
      t0 =3D vld1q_f32_x2(out);

      o0.val[0] =3D vaddq_f32(o0.val[0], t0.val[0]);
      o0.val[1] =3D vaddq_f32(o0.val[1], t0.val[1]);
    }

    // TODO: both clang and gcc generates redundant mov because of bad regi=
ster
allocation.
    vst1q_f32_x2(out, o0);
  } // end writeback
}


The assembly generated:

simple_gemm:
        movi    v3.4s, 0
        and     w4, w4, 255
        mov     v4.16b, v3.16b
        cbz     x3, .L2
.L3:
        ld1     {v0.4s - v1.4s}, [x2], 32
        subs    x3, x3, #1
        ld1r    {v2.4s}, [x1], 4
        fmla    v3.4s, v2.4s, v0.4s
        fmla    v4.4s, v2.4s, v1.4s
        bne     .L3
.L2:
        cbnz    w4, .L4
        ld1     {v0.4s - v1.4s}, [x0]
        fadd    v3.4s, v3.4s, v0.4s
        fadd    v4.4s, v4.4s, v1.4s
.L4:
        mov     v0.16b, v3.16b
        mov     v1.16b, v4.16b
        st1     {v0.4s - v1.4s}, [x0]
        ret

The two values of float32x4x2_t o0 are assigned to v3 and v4. They should be
able to be used directly as operands of st1, so the mov at L4 is redundant.=
=20=20

I also found that in some code, the register pair may not be neighboring, w=
hich
results in some redundant mov instructions.=