On Mon, 2022-06-06 at 20:31 -0400, Michael Meissner wrote:
> Optimize vec_splats of constant vec_extract for V2DI/V2DF, PR target
> 99293.
>
> This is version 3 of the patch. The original patch was:
>
> > Date: Mon, 28 Mar 2022 12:26:02 -0400
> > Subject: [PATCH 1/4] Optimize vec_splats of constant vec_extract
> > for V2DI/V2DF, PR target 99293.
> > Message-ID:
> > https://gcc.gnu.org/pipermail/gcc-patches/2022-March/592420.html
>
> Version 2 of the patch was:
>
> > Date: Fri, 13 May 2022 10:49:26 -0400
> > Subject: [PATCH] Optimize vec_splats of constant V2DI/V2DF
> > vec_extract, PR target/99293
> > Message-ID:
> > https://gcc.gnu.org/pipermail/gcc-patches/2022-May/594797.html
>
> The differences between version 2 and version 3 was to clean up the
> description
> of what the patch does, and to make the example test case clear.
>
> In PR target/99293, it was pointed out that doing:
>
> vector long long dest0, dest1, src;
> /* ... */
> dest0 = vec_splats (vec_extract (src, 0));
> dest1 = vec_splats (vec_extract (src, 1));
>
> would generate slower code.
>
> It generates the following code on power8:
>
> ;; vec_splats (vec_extract (src, 0))
> xxpermdi 0,34,34,3
> xxpermdi 34,0,0,0
>
> ;; vec_splats (vec_extract (src, 1))
> xxlor 0,34,34
> xxpermdi 34,0,0,0
>
> However on power9 and power10 it generates:
>
> ;; vec_splats (vec_extract (src, 0))
> mfvsld 3,34
> mtvsrdd 34,9,9
>
> ;; vec_splats (vec_extract (src, 1))
> mfvsrd 9,34
> mtvsrdd 34,9,9
>
> This is due to the power9 having the mfvsrld instruction which can
> extract
> either 64-bit element into a GPR. While there are alternatives for
> both
> vector registers and GPR registers, the register allocator prefers to
> put
> DImode into GPR registers.
>
> In this case, it is better to have a single combiner pattern that can
> generate
> a single xxpermdi, instead of 2 insnsns (the extract and then the
> concat).
> This is true if the two operations are move from vector register and
> move to
> vector register. As Segher pointed out in a previous version of the
> patch, the
> combiner already tries doing creating a (vec_duplicate (vec_select
> ...))
> pattern, but we didn't provide one.
>
> This patch reworks vsx_xxspltd_ for V2DImode and V2DFmode so
> that it now
> uses VEC_DUPLICATE, which the combiner checks for.
Ok.
>
> I have built Spec 2017 with this patch installed, and the cam4_r
> benchmark
> is the only benchmark that generated different code (3
> mfvsrld/mtvsrdd
> pairs of instructions were replaced with xxpermdi).
>
> I have built bootstrap versions on the following systems and I have
> run
> the regression tests. There were no regressions in the runs:
>
> Power9 little endian, --with-cpu=power9
> Power10 little endian, --with-cpu=power10
> Power8 big endian, --with-cpu=power8 (both 32-bit & 64-bit
> tests)
Ok.
>
> Can I install this into the trunk? After a burn-in period, can I
> backport
> and install this into GCC 11 and GCC 10 branches?
>
> 2022-06-06 Michael Meissner
>
> gcc/
> PR target/99293
> * config/rs6000/rs6000-p8swap.cc (rtx_is_swappable_p): Remove
> UNSPEC_VSX_XXSPLTD case.
> * config/rs6000/vsx.md (UNSPEC_VSX_XXSPLTD): Delete.
> (vsx_xxspltd_): Rewrite to use VEC_DUPLICATE.
>
> gcc/testsuite:
> PR target/99293
> * gcc.target/powerpc/builtins-1.c: Update insn count.
> * gcc.target/powerpc/pr99293.c: New test.
> ---
> gcc/config/rs6000/rs6000-p8swap.cc| 1 -
> gcc/config/rs6000/vsx.md | 19 +++
> gcc/testsuite/gcc.target/powerpc/builtins-1.c | 2 +-
> gcc/testsuite/gcc.target/powerpc/pr99293.c| 51
> +++
> 4 files changed, 62 insertions(+), 11 deletions(-)
> create mode 100644 gcc/testsuite/gcc.target/powerpc/pr99293.c
>
> diff --git a/gcc/config/rs6000/rs6000-p8swap.cc
> b/gcc/config/rs6000/rs6000-p8swap.cc
> index 275702fee1b..3160fcbdeca 100644
> --- a/gcc/config/rs6000/rs6000-p8swap.cc
> +++ b/gcc/config/rs6000/rs6000-p8swap.cc
> @@ -807,7 +807,6 @@ rtx_is_swappable_p (rtx op, unsigned int
> *special)
> case UNSPEC_VUPKLU_V4SF:
> return 0;
> case UNSPEC_VSPLT_DIRECT:
> - case UNSPEC_VSX_XXSPLTD:
> *special = SH_SPLAT;
> return 1;
> case UNSPEC_REDUC_PLUS:
> diff --git a/gcc/config/rs6000/vsx.md b/gcc/config/rs6000/vsx.md
> index 1b75538f42f..a1a1ce95195 100644
> --- a/gcc/config/rs6000/vsx.md
> +++ b/gcc/config/rs6000/vsx.md
> @@ -296,7 +296,6 @@ (define_c_enum "unspec"
> UNSPEC_VSX_XXPERM
>
> UNSPEC_VSX_XXSPLTW
> - UNSPEC_VSX_XXSPLTD
> UNSPEC_VSX_DIVSD
> UNSPEC_VSX_DIVUD
> UNSPEC_VSX_DIVSQ
Ok.
> @@ -4673,16 +4672,18 @@ (define_insn "vsx_vsplt_di"
> ;; V2DF/V2DI splat for use by vec_splat builtin
> (define_insn "vsx_xxspltd_"
>[(set (match_operand:VSX_D 0 "vsx_register_operand" "
