[PATCH] x86_64: Improved V1TImode rotations by non-constant amounts.

Uros Bizjak ubizjak@gmail.com
Sun Nov 28 19:15:57 GMT 2021


On Sun, Nov 28, 2021 at 3:02 PM Roger Sayle <roger@nextmovesoftware.com> wrote:
>
>
> This patch builds on the recent improvements to TImode rotations (and
> Jakub's fixes to shldq/shrdq patterns).  Now that expanding a TImode
> rotation can never fail, it is safe to allow general_operand constraints
> on the QImode shift amounts in rotlv1ti3 and rotrv1ti3 patterns.
> I've also made an additional tweak to ix86_expand_v1ti_to_ti to use
> vec_extract via V2DImode, which avoid using memory and takes advantage
> vpextrq on recent hardware.
>
> For the following test case:
>
> typedef unsigned __int128 uv1ti __attribute__ ((__vector_size__ (16)));
> uv1ti rotr(uv1ti x, unsigned int i) { return (x >> i) | (x << (128-i)); }
>
> GCC with -O2 -mavx2 would previously generate:
>
> rotr:   vmovdqa %xmm0, -24(%rsp)
>         movq    -16(%rsp), %rdx
>         movl    %edi, %ecx
>         xorl    %esi, %esi
>         movq    -24(%rsp), %rax
>         shrdq   %rdx, %rax
>         shrq    %cl, %rdx
>         testb   $64, %dil
>         cmovne  %rdx, %rax
>         cmovne  %rsi, %rdx
>         negl    %ecx
>         xorl    %edi, %edi
>         andl    $127, %ecx
>         vmovq   %rax, %xmm2
>         movq    -24(%rsp), %rax
>         vpinsrq $1, %rdx, %xmm2, %xmm1
>         movq    -16(%rsp), %rdx
>         shldq   %rax, %rdx
>         salq    %cl, %rax
>         testb   $64, %cl
>         cmovne  %rax, %rdx
>         cmovne  %rdi, %rax
>         vmovq   %rax, %xmm3
>         vpinsrq $1, %rdx, %xmm3, %xmm0
>         vpor    %xmm1, %xmm0, %xmm0
>         ret
>
> with this patch, we now generate:
>
> rotr:   movl    %edi, %ecx
>         vpextrq $1, %xmm0, %rax
>         vmovq   %xmm0, %rdx
>         shrdq   %rax, %rdx
>         vmovq   %xmm0, %rsi
>         shrdq   %rsi, %rax
>         andl    $64, %ecx
>         movq    %rdx, %rsi
>         cmovne  %rax, %rsi
>         cmove   %rax, %rdx
>         vmovq   %rsi, %xmm0
>         vpinsrq $1, %rdx, %xmm0, %xmm0
>         ret
>
>
> This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
> and make -k check with no new failures.  Ok for mainline?
>
>
> 2021-11-28  Roger Sayle  <roger@nextmovesoftware.com>
>
> gcc/ChangeLog
>         * config/i386/i386-expand.c (ix86_expand_v1ti_to_ti): Perform the
>         conversion via V2DImode using vec_extractv2didi on TARGET_SSE2.
>         * config/i386/sse.md (rotlv1ti3, rotrv1ti3): Change constraint
>         on QImode shift amounts from const_int_operand to general_operand.
>
> gcc/testsuite/ChangeLog
>         * gcc.target/i386/sse2-v1ti-rotate.c: New test case.

OK.

Thanks,
Uros.

>
>
> Thanks in advance,
> Roger
> --
>


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