Re: [PATCH v3 1/2] x86: Optimize strchr-avx2.S

["H.J. Lu" <hjl.tools@gmail.com>]

On Fri, Apr 23, 2021 at 12:56 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> On Fri, Apr 23, 2021 at 12:56 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> >
> > On Thu, Apr 22, 2021 at 02:04:02PM -0400, Noah Goldstein wrote:
> > > No bug. This commit optimizes strchr-avx2.S. The optimizations are all
> > > small things such as save an ALU in the alignment process, saving a
> > > few instructions in the loop return, saving some bytes in the main
> > > loop, and increasing the ILP in the return cases. test-strchr,
> > > test-strchrnul, test-wcschr, and test-wcschrnul are all passing.
> > >
> > > Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
> > > ---
> > >  sysdeps/x86_64/multiarch/strchr-avx2.S | 294 +++++++++++++++----------
> > >  1 file changed, 173 insertions(+), 121 deletions(-)
> > >
> > > diff --git a/sysdeps/x86_64/multiarch/strchr-avx2.S b/sysdeps/x86_64/multiarch/strchr-avx2.S
> > > index 25bec38b5d..220165d2ba 100644
> > > --- a/sysdeps/x86_64/multiarch/strchr-avx2.S
> > > +++ b/sysdeps/x86_64/multiarch/strchr-avx2.S
> > > @@ -49,132 +49,144 @@
> > >
> > >       .section SECTION(.text),"ax",@progbits
> > >  ENTRY (STRCHR)
> > > -     movl    %edi, %ecx
> > > -# ifndef USE_AS_STRCHRNUL
> > > -     xorl    %edx, %edx
> > > -# endif
> > > -
> > >       /* Broadcast CHAR to YMM0.      */
> > >       vmovd   %esi, %xmm0
> > > +     movl    %edi, %eax
> > > +     andl    $(PAGE_SIZE - 1), %eax
> > > +     VPBROADCAST     %xmm0, %ymm0
> > >       vpxor   %xmm9, %xmm9, %xmm9
> > > -     VPBROADCAST %xmm0, %ymm0
> > >
> > >       /* Check if we cross page boundary with one vector load.  */
> > > -     andl    $(PAGE_SIZE - 1), %ecx
> > > -     cmpl    $(PAGE_SIZE - VEC_SIZE), %ecx
> > > -     ja  L(cross_page_boundary)
> > > +     cmpl    $(PAGE_SIZE - VEC_SIZE), %eax
> > > +     ja      L(cross_page_boundary)
> > >
> > >       /* Check the first VEC_SIZE bytes.      Search for both CHAR and the
> > >          null byte.  */
> > >       vmovdqu (%rdi), %ymm8
> > > -     VPCMPEQ %ymm8, %ymm0, %ymm1
> > > -     VPCMPEQ %ymm8, %ymm9, %ymm2
> > > +     VPCMPEQ %ymm8, %ymm0, %ymm1
> > > +     VPCMPEQ %ymm8, %ymm9, %ymm2
> > >       vpor    %ymm1, %ymm2, %ymm1
> > > -     vpmovmskb %ymm1, %eax
> > > +     vpmovmskb       %ymm1, %eax
> >
> > This change isn't needed.
>
> Fixed. For the future what is the rule for when to have a tab after
> the instructions vs just a space?

I prefer if the length of <INSN> is less than a tab,

<TAB><INSN><TAB><OPERANDS>

Otherwise

<TAB><INSN><SPACE><OPERANDS>

> >
> > >       testl   %eax, %eax
> > > -     jz      L(more_vecs)
> > > +     jz      L(aligned_more)
> > >       tzcntl  %eax, %eax
> > > -     /* Found CHAR or the null byte.  */
> > > -     addq    %rdi, %rax
> > >  # ifndef USE_AS_STRCHRNUL
> > > -     cmp (%rax), %CHAR_REG
> > > -     cmovne  %rdx, %rax
> > > +     /* Found CHAR or the null byte.  */
> > > +     cmp     (%rdi, %rax), %CHAR_REG
> > > +     jne     L(zero)
> > >  # endif
> > > -L(return_vzeroupper):
> > > -     ZERO_UPPER_VEC_REGISTERS_RETURN
> > > -
> > > -     .p2align 4
> > > -L(more_vecs):
> > > -     /* Align data for aligned loads in the loop.  */
> > > -     andq    $-VEC_SIZE, %rdi
> > > -L(aligned_more):
> > > -
> > > -     /* Check the next 4 * VEC_SIZE.  Only one VEC_SIZE at a time
> > > -        since data is only aligned to VEC_SIZE.      */
> > > -     vmovdqa VEC_SIZE(%rdi), %ymm8
> > > -     addq    $VEC_SIZE, %rdi
> > > -     VPCMPEQ %ymm8, %ymm0, %ymm1
> > > -     VPCMPEQ %ymm8, %ymm9, %ymm2
> > > -     vpor    %ymm1, %ymm2, %ymm1
> > > -     vpmovmskb %ymm1, %eax
> > > -     testl   %eax, %eax
> > > -     jnz     L(first_vec_x0)
> > > -
> > > -     vmovdqa VEC_SIZE(%rdi), %ymm8
> > > -     VPCMPEQ %ymm8, %ymm0, %ymm1
> > > -     VPCMPEQ %ymm8, %ymm9, %ymm2
> > > -     vpor    %ymm1, %ymm2, %ymm1
> > > -     vpmovmskb %ymm1, %eax
> > > -     testl   %eax, %eax
> > > -     jnz     L(first_vec_x1)
> > > -
> > > -     vmovdqa (VEC_SIZE * 2)(%rdi), %ymm8
> > > -     VPCMPEQ %ymm8, %ymm0, %ymm1
> > > -     VPCMPEQ %ymm8, %ymm9, %ymm2
> > > -     vpor    %ymm1, %ymm2, %ymm1
> > > -     vpmovmskb %ymm1, %eax
> > > -     testl   %eax, %eax
> > > -     jnz     L(first_vec_x2)
> > > -
> > > -     vmovdqa (VEC_SIZE * 3)(%rdi), %ymm8
> > > -     VPCMPEQ %ymm8, %ymm0, %ymm1
> > > -     VPCMPEQ %ymm8, %ymm9, %ymm2
> > > -     vpor    %ymm1, %ymm2, %ymm1
> > > -     vpmovmskb %ymm1, %eax
> > > -     testl   %eax, %eax
> > > -     jz      L(prep_loop_4x)
> > > +     addq    %rdi, %rax
> > > +     VZEROUPPER_RETURN
> > >
> > > +     /* .p2align 5 helps keep performance more consistent if ENTRY()
> > > +        alignment % 32 was either 16 or 0. As well this makes the
> > > +        alignment % 32 of the loop_4x_vec fixed which makes tuning it
> > > +        easier.  */
> > > +     .p2align 5
> > > +L(first_vec_x4):
> > >       tzcntl  %eax, %eax
> > > -     leaq    (VEC_SIZE * 3)(%rdi, %rax), %rax
> > > +     addq    $(VEC_SIZE * 3 + 1), %rdi
> > >  # ifndef USE_AS_STRCHRNUL
> > > -     cmp (%rax), %CHAR_REG
> > > -     cmovne  %rdx, %rax
> > > +     /* Found CHAR or the null byte.  */
> > > +     cmp     (%rdi, %rax), %CHAR_REG
> > > +     jne     L(zero)
> > >  # endif
> > > +     addq    %rdi, %rax
> > >       VZEROUPPER_RETURN
> > >
> > > -     .p2align 4
> > > -L(first_vec_x0):
> > > -     tzcntl  %eax, %eax
> > > -     /* Found CHAR or the null byte.  */
> > > -     addq    %rdi, %rax
> > >  # ifndef USE_AS_STRCHRNUL
> > > -     cmp (%rax), %CHAR_REG
> > > -     cmovne  %rdx, %rax
> > > -# endif
> > > +L(zero):
> > > +     xorl    %eax, %eax
> > >       VZEROUPPER_RETURN
> > > +# endif
> > > +
> > >
> > >       .p2align 4
> > >  L(first_vec_x1):
> > >       tzcntl  %eax, %eax
> > > -     leaq    VEC_SIZE(%rdi, %rax), %rax
> > > +     incq    %rdi
> > >  # ifndef USE_AS_STRCHRNUL
> > > -     cmp (%rax), %CHAR_REG
> > > -     cmovne  %rdx, %rax
> > > +     /* Found CHAR or the null byte.  */
> > > +     cmp     (%rdi, %rax), %CHAR_REG
> > > +     jne     L(zero)
> > >  # endif
> > > +     addq    %rdi, %rax
> > >       VZEROUPPER_RETURN
> > >
> > >       .p2align 4
> > >  L(first_vec_x2):
> > >       tzcntl  %eax, %eax
> > > +     addq    $(VEC_SIZE + 1), %rdi
> > > +# ifndef USE_AS_STRCHRNUL
> > >       /* Found CHAR or the null byte.  */
> > > -     leaq    (VEC_SIZE * 2)(%rdi, %rax), %rax
> > > +     cmp     (%rdi, %rax), %CHAR_REG
> > > +     jne     L(zero)
> > > +# endif
> > > +     addq    %rdi, %rax
> > > +     VZEROUPPER_RETURN
> > > +
> > > +     .p2align 4
> > > +L(first_vec_x3):
> > > +     tzcntl  %eax, %eax
> > > +     addq    $(VEC_SIZE * 2 + 1), %rdi
> > >  # ifndef USE_AS_STRCHRNUL
> > > -     cmp (%rax), %CHAR_REG
> > > -     cmovne  %rdx, %rax
> > > +     /* Found CHAR or the null byte.  */
> > > +     cmp     (%rdi, %rax), %CHAR_REG
> > > +     jne     L(zero)
> > >  # endif
> > > +     addq    %rdi, %rax
> > >       VZEROUPPER_RETURN
> > >
> > > -L(prep_loop_4x):
> > > -     /* Align data to 4 * VEC_SIZE.  */
> > > -     andq    $-(VEC_SIZE * 4), %rdi
> > > +     .p2align 4
> > > +L(aligned_more):
> > > +     /* Align data to VEC_SIZE - 1. This is the same number of
> > > +        instructions as using andq -VEC_SIZE but saves 4 bytes of code on
> > > +        x4 check.  */
> > > +     orq     $(VEC_SIZE - 1), %rdi
> > > +L(cross_page_continue):
> > > +     /* Check the next 4 * VEC_SIZE.  Only one VEC_SIZE at a time since
> > > +        data is only aligned to VEC_SIZE.  */
> > > +     vmovdqa 1(%rdi), %ymm8
> > > +     VPCMPEQ %ymm8, %ymm0, %ymm1
> > > +     VPCMPEQ %ymm8, %ymm9, %ymm2
> > > +     vpor    %ymm1, %ymm2, %ymm1
> > > +     vpmovmskb       %ymm1, %eax
> >
> > Use a space, not tab, after vpmovmskb.
>
> Fixed.
>
> >
> > > +     testl   %eax, %eax
> > > +     jnz     L(first_vec_x1)
> > >
> > > +     vmovdqa (VEC_SIZE + 1)(%rdi), %ymm8
> > > +     VPCMPEQ %ymm8, %ymm0, %ymm1
> > > +     VPCMPEQ %ymm8, %ymm9, %ymm2
> > > +     vpor    %ymm1, %ymm2, %ymm1
> > > +     vpmovmskb       %ymm1, %eax
> >
> > Use a space, not tab, after vpmovmskb.
> >
>
> Fixed.
>
> > > +     testl   %eax, %eax
> > > +     jnz     L(first_vec_x2)
> > > +
> > > +     vmovdqa (VEC_SIZE * 2 + 1)(%rdi), %ymm8
> > > +     VPCMPEQ %ymm8, %ymm0, %ymm1
> > > +     VPCMPEQ %ymm8, %ymm9, %ymm2
> > > +     vpor    %ymm1, %ymm2, %ymm1
> > > +     vpmovmskb       %ymm1, %eax
> >
> > Use a space, not tab, after vpmovmskb.
> >
>
> Fixed.
>
> > > +     testl   %eax, %eax
> > > +     jnz     L(first_vec_x3)
> > > +
> > > +     vmovdqa (VEC_SIZE * 3 + 1)(%rdi), %ymm8
> > > +     VPCMPEQ %ymm8, %ymm0, %ymm1
> > > +     VPCMPEQ %ymm8, %ymm9, %ymm2
> > > +     vpor    %ymm1, %ymm2, %ymm1
> > > +     vpmovmskb       %ymm1, %eax
> >
> > Use a space, not tab, after vpmovmskb.
> >
>
> Fixed.
>
> > > +     testl   %eax, %eax
> > > +     jnz     L(first_vec_x4)
> > > +     /* Align data to VEC_SIZE * 4 - 1.      */
> > > +     addq    $(VEC_SIZE * 4 + 1), %rdi
> > > +     andq    $-(VEC_SIZE * 4), %rdi
> > >       .p2align 4
> > >  L(loop_4x_vec):
> > >       /* Compare 4 * VEC at a time forward.  */
> > > -     vmovdqa (VEC_SIZE * 4)(%rdi), %ymm5
> > > -     vmovdqa (VEC_SIZE * 5)(%rdi), %ymm6
> > > -     vmovdqa (VEC_SIZE * 6)(%rdi), %ymm7
> > > -     vmovdqa (VEC_SIZE * 7)(%rdi), %ymm8
> > > +     vmovdqa (%rdi), %ymm5
> > > +     vmovdqa (VEC_SIZE)(%rdi), %ymm6
> > > +     vmovdqa (VEC_SIZE * 2)(%rdi), %ymm7
> > > +     vmovdqa (VEC_SIZE * 3)(%rdi), %ymm8
> > >
> > >       /* Leaves only CHARS matching esi as 0.  */
> > >       vpxor   %ymm5, %ymm0, %ymm1
> > > @@ -190,62 +202,102 @@ L(loop_4x_vec):
> > >       VPMINU  %ymm1, %ymm2, %ymm5
> > >       VPMINU  %ymm3, %ymm4, %ymm6
> > >
> > > -     VPMINU  %ymm5, %ymm6, %ymm5
> > > +     VPMINU  %ymm5, %ymm6, %ymm6
> > >
> > > -     VPCMPEQ %ymm5, %ymm9, %ymm5
> > > -     vpmovmskb %ymm5, %eax
> > > +     VPCMPEQ %ymm6, %ymm9, %ymm6
> > > +     vpmovmskb       %ymm6, %ecx
> >
> > Use a space, not tab, after vpmovmskb.
> >
>
> Fixed.
>
> > > +     subq    $-(VEC_SIZE * 4), %rdi
> > > +     testl   %ecx, %ecx
> > > +     jz      L(loop_4x_vec)
> > >
> > > -     addq    $(VEC_SIZE * 4), %rdi
> > > -     testl   %eax, %eax
> > > -     jz  L(loop_4x_vec)
> > >
> > > -     VPCMPEQ %ymm1, %ymm9, %ymm1
> > > -     vpmovmskb %ymm1, %eax
> > > +     VPCMPEQ %ymm1, %ymm9, %ymm1
> > > +     vpmovmskb       %ymm1, %eax
> >
> > Use a space, not tab, after vpmovmskb.
> >
>
> Fixed.
>
> > >       testl   %eax, %eax
> > > -     jnz     L(first_vec_x0)
> > > +     jnz     L(last_vec_x0)
> > > +
> > >
> > > -     VPCMPEQ %ymm2, %ymm9, %ymm2
> > > -     vpmovmskb %ymm2, %eax
> > > +     VPCMPEQ %ymm5, %ymm9, %ymm2
> > > +     vpmovmskb       %ymm2, %eax
> >
> > Use a space, not tab, after vpmovmskb.
> >
>
> Fixed.
>
> > >       testl   %eax, %eax
> > > -     jnz     L(first_vec_x1)
> > > +     jnz     L(last_vec_x1)
> > > +
> > > +     VPCMPEQ %ymm3, %ymm9, %ymm3
> > > +     vpmovmskb       %ymm3, %eax
> > > +     /* rcx has combined result from all 4 VEC. It will only be used if
> > > +        the first 3 other VEC all did not contain a match.  */
> > > +     salq    $32, %rcx
> > > +     orq     %rcx, %rax
> > > +     tzcntq  %rax, %rax
> > > +     subq    $(VEC_SIZE * 2), %rdi
> > > +# ifndef USE_AS_STRCHRNUL
> > > +     /* Found CHAR or the null byte.  */
> > > +     cmp     (%rdi, %rax), %CHAR_REG
> > > +     jne     L(zero_end)
> > > +# endif
> > > +     addq    %rdi, %rax
> > > +     VZEROUPPER_RETURN
> > > +
> > >
> > > -     VPCMPEQ %ymm3, %ymm9, %ymm3
> > > -     VPCMPEQ %ymm4, %ymm9, %ymm4
> > > -     vpmovmskb %ymm3, %ecx
> > > -     vpmovmskb %ymm4, %eax
> > > -     salq    $32, %rax
> > > -     orq %rcx, %rax
> > > -     tzcntq  %rax, %rax
> > > -     leaq    (VEC_SIZE * 2)(%rdi, %rax), %rax
> > > +     .p2align 4
> > > +L(last_vec_x0):
> > > +     tzcntl  %eax, %eax
> > > +     addq    $-(VEC_SIZE * 4), %rdi
> > >  # ifndef USE_AS_STRCHRNUL
> > > -     cmp (%rax), %CHAR_REG
> > > -     cmovne  %rdx, %rax
> > > +     /* Found CHAR or the null byte.  */
> > > +     cmp     (%rdi, %rax), %CHAR_REG
> > > +     jne     L(zero_end)
> > >  # endif
> > > +     addq    %rdi, %rax
> > >       VZEROUPPER_RETURN
> > >
> > > +# ifndef USE_AS_STRCHRNUL
> > > +L(zero_end):
> > > +     xorl    %eax, %eax
> > > +     VZEROUPPER_RETURN
> > > +# endif
> > > +
> > > +     .p2align 4
> > > +L(last_vec_x1):
> > > +     tzcntl  %eax, %eax
> > > +     subq    $(VEC_SIZE * 3), %rdi
> > > +# ifndef USE_AS_STRCHRNUL
> > > +     /* Found CHAR or the null byte.  */
> > > +     cmp     (%rdi, %rax), %CHAR_REG
> > > +     jne     L(zero_end)
> > > +# endif
> > > +     addq    %rdi, %rax
> > > +     VZEROUPPER_RETURN
> > > +
> > > +
> > >       /* Cold case for crossing page with first load.  */
> > >       .p2align 4
> > >  L(cross_page_boundary):
> > > -     andq    $-VEC_SIZE, %rdi
> > > -     andl    $(VEC_SIZE - 1), %ecx
> > > -
> > > -     vmovdqa (%rdi), %ymm8
> > > -     VPCMPEQ %ymm8, %ymm0, %ymm1
> > > -     VPCMPEQ %ymm8, %ymm9, %ymm2
> > > +     movq    %rdi, %rdx
> > > +     /* Align rdi to VEC_SIZE - 1.  */
> > > +     orq     $(VEC_SIZE - 1), %rdi
> > > +     vmovdqa -(VEC_SIZE - 1)(%rdi), %ymm8
> > > +     VPCMPEQ %ymm8, %ymm0, %ymm1
> > > +     VPCMPEQ %ymm8, %ymm9, %ymm2
> > >       vpor    %ymm1, %ymm2, %ymm1
> > > -     vpmovmskb %ymm1, %eax
> > > -     /* Remove the leading bits.      */
> > > -     sarxl   %ecx, %eax, %eax
> > > +     vpmovmskb       %ymm1, %eax
> > > +     /* Remove the leading bytes. sarxl only uses bits [5:0] of COUNT
> > > +        so no need to manually mod edx.  */
> > > +     sarxl   %edx, %eax, %eax
> > >       testl   %eax, %eax
> > > -     jz      L(aligned_more)
> > > +     jz      L(cross_page_continue)
> > >       tzcntl  %eax, %eax
> > > -     addq    %rcx, %rdi
> > > -     addq    %rdi, %rax
> > >  # ifndef USE_AS_STRCHRNUL
> > > -     cmp (%rax), %CHAR_REG
> > > -     cmovne  %rdx, %rax
> > > +     xorl    %ecx, %ecx
> > > +     /* Found CHAR or the null byte.  */
> > > +     cmp     (%rdx, %rax), %CHAR_REG
> > > +     leaq    (%rdx, %rax), %rax
> > > +     cmovne  %rcx, %rax
> > > +# else
> > > +     addq    %rdx, %rax
> > >  # endif
> > > -     VZEROUPPER_RETURN
> > > +L(return_vzeroupper):
> > > +     ZERO_UPPER_VEC_REGISTERS_RETURN
> > >
> > >  END (STRCHR)
> > >  # endif
> > > --
> > > 2.29.2
> > >
> >
> > Thanks.
> >
> > H.J.



-- 
H.J.