Re: [PATCH] Improve QImode extraction without SSE4.1 (PR tree-optimization/91201)

[Uros Bizjak <ubizjak at gmail dot com>]

On Fri, Aug 2, 2019 at 9:54 AM Jakub Jelinek <jakub@redhat.com> wrote:
>
> Hi!
>
> As mentioned in the PR, for SSE4.1 we use pextrb for vec_extractv16qiqi,
> but at least for element 0 we store the vector into memory and load the
> single byte from there and we can just use movd instead.
>
> The following patch does that, just skips it for the case when we know we'll
> go through memory anyway.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> For the non-Os case, perhaps we could also handle other (elt & 3) == 0 cases
> which V4SImode ix86_expand_vector_extract also handles through shuffles
> (pshufd or unpck*) before the movd, just not sure if it is a win.
>
> 2019-08-01  Jakub Jelinek  <jakub@redhat.com>
>
>         PR tree-optimization/91201
>         * config/i386/i386-expand.c (ix86_expand_vector_extract): For elt == 0
>         V16QImode extraction without sse4.1 try to use V4SImode lowpart
>         extraction.
>
>         * gcc.target/i386/sse2-pr91201-3.c: New test.
>         * gcc.target/i386/sse2-pr91201-4.c: New test.
>         * gcc.target/i386/sse2-pr91201-5.c: New test.
>         * gcc.target/i386/sse2-pr91201-6.c: New test.

OK.

Thanks,
Uros.

> --- gcc/config/i386/i386-expand.c.jj    2019-07-30 09:12:34.578959902 +0200
> +++ gcc/config/i386/i386-expand.c       2019-08-01 10:41:22.545887899 +0200
> @@ -14706,6 +14706,17 @@ ix86_expand_vector_extract (bool mmx_ok,
>
>      case E_V16QImode:
>        use_vec_extr = TARGET_SSE4_1;
> +      if (!use_vec_extr
> +         && TARGET_SSE2
> +         && elt == 0
> +         && (optimize_insn_for_size_p () || TARGET_INTER_UNIT_MOVES_FROM_VEC))
> +       {
> +         tmp = gen_reg_rtx (SImode);
> +         ix86_expand_vector_extract (false, tmp, gen_lowpart (V4SImode, vec),
> +                                     0);
> +         emit_insn (gen_rtx_SET (target, gen_lowpart (QImode, tmp)));
> +         return;
> +       }
>        break;
>
>      case E_V8SFmode:
> --- gcc/testsuite/gcc.target/i386/sse2-pr91201-3.c.jj   2019-08-01 10:59:07.508887273 +0200
> +++ gcc/testsuite/gcc.target/i386/sse2-pr91201-3.c      2019-08-01 11:07:42.925165205 +0200
> @@ -0,0 +1,13 @@
> +/* PR tree-optimization/91201 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -msse2 -mno-sse3 -mtune=generic -masm=att" } */
> +/* { dg-final { scan-assembler "\tmovd\t%xmm0, %eax" } } */
> +/* { dg-final { scan-assembler-not "\\(%" } } */
> +
> +typedef unsigned char V __attribute__((vector_size (16)));
> +
> +unsigned char
> +foo (V x)
> +{
> +  return x[0];
> +}
> --- gcc/testsuite/gcc.target/i386/sse2-pr91201-4.c.jj   2019-08-01 10:59:33.539497274 +0200
> +++ gcc/testsuite/gcc.target/i386/sse2-pr91201-4.c      2019-08-01 11:07:35.304279381 +0200
> @@ -0,0 +1,13 @@
> +/* PR tree-optimization/91201 */
> +/* { dg-do compile } */
> +/* { dg-options "-Os -msse2 -mno-sse3 -mtune=generic -masm=att" } */
> +/* { dg-final { scan-assembler "\tmovd\t%xmm0, %eax" } } */
> +/* { dg-final { scan-assembler-not "\\(%" } } */
> +
> +typedef unsigned char V __attribute__((vector_size (16)));
> +
> +unsigned char
> +foo (V x)
> +{
> +  return x[0];
> +}
> --- gcc/testsuite/gcc.target/i386/sse2-pr91201-5.c.jj   2019-08-01 11:01:07.994082143 +0200
> +++ gcc/testsuite/gcc.target/i386/sse2-pr91201-5.c      2019-08-01 11:07:19.230520198 +0200
> @@ -0,0 +1,13 @@
> +/* PR tree-optimization/91201 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -msse2 -mno-sse3 -mtune=k8 -masm=att" } */
> +/* { dg-final { scan-assembler-not "\tmovd\t%xmm0, %eax" } } */
> +/* { dg-final { scan-assembler "\tmov(zbl|b)\t\[^\n\r]*\\(%" } } */
> +
> +typedef unsigned char V __attribute__((vector_size (16)));
> +
> +unsigned char
> +foo (V x)
> +{
> +  return x[0];
> +}
> --- gcc/testsuite/gcc.target/i386/sse2-pr91201-6.c.jj   2019-08-01 11:03:34.896881216 +0200
> +++ gcc/testsuite/gcc.target/i386/sse2-pr91201-6.c      2019-08-01 11:07:27.564395340 +0200
> @@ -0,0 +1,13 @@
> +/* PR tree-optimization/91201 */
> +/* { dg-do compile } */
> +/* { dg-options "-Os -msse2 -mno-sse3 -mtune=k8 -masm=att" } */
> +/* { dg-final { scan-assembler "\tmovd\t%xmm0, %eax" } } */
> +/* { dg-final { scan-assembler-not "\\(%" } } */
> +
> +typedef unsigned char V __attribute__((vector_size (16)));
> +
> +unsigned char
> +foo (V x)
> +{
> +  return x[0];
> +}
>
>         Jakub