[v1,2/2] x86: Optimize strlen-avx2.S

  No bug. This commit optimizes strlen-avx2.S. The optimizations are
mostly small things but they add up to roughly 10-30% performance
improvement for strlen. The results for strnlen are bit more
ambiguous. test-strlen, test-strnlen, test-wcslen, and test-wcsnlen
are all passing.

Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
---
 sysdeps/x86_64/multiarch/strlen-avx2-rtm.S |   2 +-
 sysdeps/x86_64/multiarch/strlen-avx2.S     | 519 ++++++++++++---------
 2 files changed, 311 insertions(+), 210 deletions(-)
  

On Fri, Apr 16, 2021 at 7:53 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> No bug. This commit optimizes strlen-avx2.S. The optimizations are
> mostly small things but they add up to roughly 10-30% performance
> improvement for strlen. The results for strnlen are bit more
> ambiguous. test-strlen, test-strnlen, test-wcslen, and test-wcsnlen
> are all passing.
>
> Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
> ---
>  sysdeps/x86_64/multiarch/strlen-avx2-rtm.S |   2 +-
>  sysdeps/x86_64/multiarch/strlen-avx2.S     | 519 ++++++++++++---------
>  2 files changed, 311 insertions(+), 210 deletions(-)
>
> diff --git a/sysdeps/x86_64/multiarch/strlen-avx2-rtm.S b/sysdeps/x86_64/multiarch/strlen-avx2-rtm.S
> index 75b4b7612c..50d40da0fb 100644
> --- a/sysdeps/x86_64/multiarch/strlen-avx2-rtm.S
> +++ b/sysdeps/x86_64/multiarch/strlen-avx2-rtm.S
> @@ -6,7 +6,7 @@
>    ZERO_UPPER_VEC_REGISTERS_RETURN_XTEST
>
>  #define VZEROUPPER_RETURN jmp   L(return_vzeroupper)
> -
> +#define USE_IN_RTM 1

No need for this change.

>  #define SECTION(p) p##.avx.rtm
>
>  #include "strlen-avx2.S"
> diff --git a/sysdeps/x86_64/multiarch/strlen-avx2.S b/sysdeps/x86_64/multiarch/strlen-avx2.S
> index 1caae9e6bc..7d76f4ed71 100644
> --- a/sysdeps/x86_64/multiarch/strlen-avx2.S
> +++ b/sysdeps/x86_64/multiarch/strlen-avx2.S
> @@ -27,9 +27,11 @@
>  # ifdef USE_AS_WCSLEN
>  #  define VPCMPEQ      vpcmpeqd
>  #  define VPMINU       vpminud
> +#  define CHAR_SIZE    4
>  # else
>  #  define VPCMPEQ      vpcmpeqb
>  #  define VPMINU       vpminub
> +#  define CHAR_SIZE    1
>  # endif
>
>  # ifndef VZEROUPPER
> @@ -41,349 +43,448 @@
>  # endif
>
>  # define VEC_SIZE 32
> +# define PAGE_SIZE 4096
>
>         .section SECTION(.text),"ax",@progbits
>  ENTRY (STRLEN)
>  # ifdef USE_AS_STRNLEN
> -       /* Check for zero length.  */
> +       /* Check zero length.  */
>         test    %RSI_LP, %RSI_LP
>         jz      L(zero)
> +       mov     %RSI_LP, %R8_LP

Please add a comment to explain this change.

>  #  ifdef USE_AS_WCSLEN
>         shl     $2, %RSI_LP
>  #  elif defined __ILP32__
>         /* Clear the upper 32 bits.  */
>         movl    %esi, %esi
>  #  endif
> -       mov     %RSI_LP, %R8_LP
>  # endif
> -       movl    %edi, %ecx
> +       movl    %edi, %eax
>         movq    %rdi, %rdx
> +       sall    $20, %eax

Please add a comment to explain this change.

>         vpxor   %xmm0, %xmm0, %xmm0
> -
>         /* Check if we may cross page boundary with one vector load.  */
> -       andl    $(2 * VEC_SIZE - 1), %ecx
> -       cmpl    $VEC_SIZE, %ecx
> -       ja      L(cros_page_boundary)
> +       cmpl    $((PAGE_SIZE - VEC_SIZE) << 20), %eax

Please add a comment to explain this change and add comments
to all changes which are 100% obvious.

> +       ja      L(cross_page_boundary)
>
>         /* Check the first VEC_SIZE bytes.  */
> -       VPCMPEQ (%rdi), %ymm0, %ymm1
> -       vpmovmskb %ymm1, %eax
> -       testl   %eax, %eax
> -
> +       VPCMPEQ (%rdi), %ymm0, %ymm1
> +       vpmovmskb       %ymm1, %eax
>  # ifdef USE_AS_STRNLEN
> -       jnz     L(first_vec_x0_check)
> -       /* Adjust length and check the end of data.  */
> -       subq    $VEC_SIZE, %rsi
> -       jbe     L(max)
> -# else
> -       jnz     L(first_vec_x0)
> +       /* If length < VEC_SIZE handle special.  */
> +       cmpq    $VEC_SIZE, %rsi
> +       jbe     L(first_vec_x0)
>  # endif
> -
> -       /* Align data for aligned loads in the loop.  */
> -       addq    $VEC_SIZE, %rdi
> -       andl    $(VEC_SIZE - 1), %ecx
> -       andq    $-VEC_SIZE, %rdi
> +       testl   %eax, %eax
> +       jz      L(aligned_more)
> +       tzcntl  %eax, %eax
> +# ifdef USE_AS_WCSLEN
> +       shrl    $2, %eax
> +# endif
> +       VZEROUPPER_RETURN
>
>  # ifdef USE_AS_STRNLEN
> -       /* Adjust length.  */
> -       addq    %rcx, %rsi
> +L(zero):
> +       xorl    %eax, %eax
> +       ret
>
> -       subq    $(VEC_SIZE * 4), %rsi
> -       jbe     L(last_4x_vec_or_less)
> +       .p2align 4
> +L(first_vec_x0):
> +       /* Select min of length and position of first null.  */
> +       btsq    %rsi, %rax
> +       tzcntl  %eax, %eax
> +#  ifdef USE_AS_WCSLEN
> +       shrl    $2, %eax
> +#  endif
> +       VZEROUPPER_RETURN
>  # endif
> -       jmp     L(more_4x_vec)
>
>         .p2align 4
> -L(cros_page_boundary):
> -       andl    $(VEC_SIZE - 1), %ecx
> -       andq    $-VEC_SIZE, %rdi
> -       VPCMPEQ (%rdi), %ymm0, %ymm1
> -       vpmovmskb %ymm1, %eax
> -       /* Remove the leading bytes.  */
> -       sarl    %cl, %eax
> -       testl   %eax, %eax
> -       jz      L(aligned_more)
> +L(first_vec_x1):
>         tzcntl  %eax, %eax
> +       /* Safe to use 32 bit instructions as these are only called for
> +          size = [1, 159].  */
>  # ifdef USE_AS_STRNLEN
> -       /* Check the end of data.  */
> -       cmpq    %rax, %rsi
> -       jbe     L(max)
> +       /* Use ecx which was computed earlier to compute correct value.
> +       */
> +       subl    $(VEC_SIZE * 4 + 1), %ecx
> +       addl    %ecx, %eax
> +# else
> +       subl    %edx, %edi
> +       incl    %edi
> +       addl    %edi, %eax
>  # endif
> -       addq    %rdi, %rax
> -       addq    %rcx, %rax
> -       subq    %rdx, %rax
>  # ifdef USE_AS_WCSLEN
> -       shrq    $2, %rax
> +       shrl    $2, %eax
>  # endif
> -L(return_vzeroupper):
> -       ZERO_UPPER_VEC_REGISTERS_RETURN
> +       VZEROUPPER_RETURN
>
>         .p2align 4
> -L(aligned_more):
> +L(first_vec_x2):
> +       tzcntl  %eax, %eax
> +       /* Safe to use 32 bit instructions as these are only called for
> +          size = [1, 159].  */
>  # ifdef USE_AS_STRNLEN
> -        /* "rcx" is less than VEC_SIZE.  Calculate "rdx + rcx - VEC_SIZE"
> -           with "rdx - (VEC_SIZE - rcx)" instead of "(rdx + rcx) - VEC_SIZE"
> -           to void possible addition overflow.  */
> -       negq    %rcx
> -       addq    $VEC_SIZE, %rcx
> -
> -       /* Check the end of data.  */
> -       subq    %rcx, %rsi
> -       jbe     L(max)
> +       /* Use ecx which was computed earlier to compute correct value.
> +       */
> +       subl    $(VEC_SIZE * 3 + 1), %ecx
> +       addl    %ecx, %eax
> +# else
> +       subl    %edx, %edi
> +       addl    $(VEC_SIZE + 1), %edi
> +       addl    %edi, %eax
>  # endif
> +# ifdef USE_AS_WCSLEN
> +       shrl    $2, %eax
> +# endif
> +       VZEROUPPER_RETURN
>
> -       addq    $VEC_SIZE, %rdi
> +       .p2align 4
> +L(first_vec_x3):
> +       tzcntl  %eax, %eax
> +       /* Safe to use 32 bit instructions as these are only called for
> +          size = [1, 159].  */
> +# ifdef USE_AS_STRNLEN
> +       /* Use ecx which was computed earlier to compute correct value.
> +       */
> +       subl    $(VEC_SIZE * 2 + 1), %ecx
> +       addl    %ecx, %eax
> +# else
> +       subl    %edx, %edi
> +       addl    $(VEC_SIZE * 2 + 1), %edi
> +       addl    %edi, %eax
> +# endif
> +# ifdef USE_AS_WCSLEN
> +       shrl    $2, %eax
> +# endif
> +       VZEROUPPER_RETURN
>
> +       .p2align 4
> +L(first_vec_x4):
> +       tzcntl  %eax, %eax
> +       /* Safe to use 32 bit instructions as these are only called for
> +          size = [1, 159].  */
>  # ifdef USE_AS_STRNLEN
> -       subq    $(VEC_SIZE * 4), %rsi
> -       jbe     L(last_4x_vec_or_less)
> +       /* Use ecx which was computed earlier to compute correct value.
> +       */
> +       subl    $(VEC_SIZE + 1), %ecx
> +       addl    %ecx, %eax
> +# else
> +       subl    %edx, %edi
> +       addl    $(VEC_SIZE * 3 + 1), %edi
> +       addl    %edi, %eax
>  # endif
> +# ifdef USE_AS_WCSLEN
> +       shrl    $2, %eax
> +# endif
> +       VZEROUPPER_RETURN
>
> -L(more_4x_vec):
> +       .p2align 5
> +L(aligned_more):
> +       /* Align data to VEC_SIZE - 1.  */
> +       orq     $(VEC_SIZE - 1), %rdi
> +L(cross_page_continue):
>         /* Check the first 4 * VEC_SIZE.  Only one VEC_SIZE at a time
>            since data is only aligned to VEC_SIZE.  */
> -       VPCMPEQ (%rdi), %ymm0, %ymm1
> -       vpmovmskb %ymm1, %eax
> -       testl   %eax, %eax
> -       jnz     L(first_vec_x0)
> -
> -       VPCMPEQ VEC_SIZE(%rdi), %ymm0, %ymm1
> -       vpmovmskb %ymm1, %eax
> +# ifdef USE_AS_STRNLEN
> +       /* + 1 because rdi is aligned to VEC_SIZE - 1. + CHAR_SIZE because
> +          it simplies the logic in last_4x_vec_or_less.  */
> +       leaq    (VEC_SIZE * 4 + CHAR_SIZE + 1)(%rdi), %rcx
> +       subq    %rdx, %rcx
> +# endif
> +       /* Load first VEC regardless.  */
> +       VPCMPEQ 1(%rdi), %ymm0, %ymm1
> +# ifdef USE_AS_STRNLEN
> +       /* Adjust length. If near end handle specially.  */
> +       subq    %rcx, %rsi
> +       jb      L(last_4x_vec_or_less)
> +# endif
> +       vpmovmskb       %ymm1, %eax
>         testl   %eax, %eax
>         jnz     L(first_vec_x1)
>
> -       VPCMPEQ (VEC_SIZE * 2)(%rdi), %ymm0, %ymm1
> -       vpmovmskb %ymm1, %eax
> +       VPCMPEQ (VEC_SIZE + 1)(%rdi), %ymm0, %ymm1
> +       vpmovmskb       %ymm1, %eax
>         testl   %eax, %eax
>         jnz     L(first_vec_x2)
>
> -       VPCMPEQ (VEC_SIZE * 3)(%rdi), %ymm0, %ymm1
> -       vpmovmskb %ymm1, %eax
> +       VPCMPEQ (VEC_SIZE * 2 + 1)(%rdi), %ymm0, %ymm1
> +       vpmovmskb       %ymm1, %eax
>         testl   %eax, %eax
>         jnz     L(first_vec_x3)
>
> -       addq    $(VEC_SIZE * 4), %rdi
> -
> -# ifdef USE_AS_STRNLEN
> -       subq    $(VEC_SIZE * 4), %rsi
> -       jbe     L(last_4x_vec_or_less)
> -# endif
> -
> -       /* Align data to 4 * VEC_SIZE.  */
> -       movq    %rdi, %rcx
> -       andl    $(4 * VEC_SIZE - 1), %ecx
> -       andq    $-(4 * VEC_SIZE), %rdi
> +       VPCMPEQ (VEC_SIZE * 3 + 1)(%rdi), %ymm0, %ymm1
> +       vpmovmskb       %ymm1, %eax
> +       testl   %eax, %eax
> +       jnz     L(first_vec_x4)
>
> +       /* Align data to VEC_SIZE * 4 - 1.  */
>  # ifdef USE_AS_STRNLEN
> -       /* Adjust length.  */
> +       /* Before adjusting length check if at last VEC_SIZE * 4.  */
> +       cmpq    $(VEC_SIZE * 4 - 1), %rsi
> +       jbe     L(last_4x_vec_or_less_load)
> +       incq    %rdi
> +       movl    %edi, %ecx
> +       orq     $(VEC_SIZE * 4 - 1), %rdi
> +       andl    $(VEC_SIZE * 4 - 1), %ecx
> +       /* Readjust length.  */
>         addq    %rcx, %rsi
> +# else
> +       incq    %rdi
> +       orq     $(VEC_SIZE * 4 - 1), %rdi
>  # endif
> -
> +       /* Compare 4 * VEC at a time forward.  */
>         .p2align 4
>  L(loop_4x_vec):
> -       /* Compare 4 * VEC at a time forward.  */
> -       vmovdqa (%rdi), %ymm1
> -       vmovdqa VEC_SIZE(%rdi), %ymm2
> -       vmovdqa (VEC_SIZE * 2)(%rdi), %ymm3
> -       vmovdqa (VEC_SIZE * 3)(%rdi), %ymm4
> -       VPMINU  %ymm1, %ymm2, %ymm5
> -       VPMINU  %ymm3, %ymm4, %ymm6
> -       VPMINU  %ymm5, %ymm6, %ymm5
> -
> -       VPCMPEQ %ymm5, %ymm0, %ymm5
> -       vpmovmskb %ymm5, %eax
> -       testl   %eax, %eax
> -       jnz     L(4x_vec_end)
> -
> -       addq    $(VEC_SIZE * 4), %rdi
> -
> -# ifndef USE_AS_STRNLEN
> -       jmp     L(loop_4x_vec)
> -# else
> +# ifdef USE_AS_STRNLEN
> +       /* Break if at end of length.  */
>         subq    $(VEC_SIZE * 4), %rsi
> -       ja      L(loop_4x_vec)
> +       jb      L(last_4x_vec_or_less_cmpeq)
> +# endif
> +       vmovdqa 1(%rdi), %ymm1
> +       VPMINU  (VEC_SIZE + 1)(%rdi), %ymm1, %ymm2
> +       vmovdqa (VEC_SIZE * 2 + 1)(%rdi), %ymm3
> +       VPMINU  (VEC_SIZE * 3 + 1)(%rdi), %ymm3, %ymm4
>
> -L(last_4x_vec_or_less):
> -       /* Less than 4 * VEC and aligned to VEC_SIZE.  */
> -       addl    $(VEC_SIZE * 2), %esi
> -       jle     L(last_2x_vec)
> +       VPMINU  %ymm2, %ymm4, %ymm5
> +       VPCMPEQ %ymm5, %ymm0, %ymm5
> +       vpmovmskb       %ymm5, %ecx
>
> -       VPCMPEQ (%rdi), %ymm0, %ymm1
> -       vpmovmskb %ymm1, %eax
> -       testl   %eax, %eax
> -       jnz     L(first_vec_x0)
> +       subq    $-(VEC_SIZE * 4), %rdi
> +       testl   %ecx, %ecx
> +       jz      L(loop_4x_vec)
>
> -       VPCMPEQ VEC_SIZE(%rdi), %ymm0, %ymm1
> -       vpmovmskb %ymm1, %eax
> -       testl   %eax, %eax
> -       jnz     L(first_vec_x1)
>
> -       VPCMPEQ (VEC_SIZE * 2)(%rdi), %ymm0, %ymm1
> -       vpmovmskb %ymm1, %eax
> +       VPCMPEQ %ymm1, %ymm0, %ymm1
> +       vpmovmskb       %ymm1, %eax
> +       subq    %rdx, %rdi
>         testl   %eax, %eax
> +       jnz     L(last_vec_return_x0)
>
> -       jnz     L(first_vec_x2_check)
> -       subl    $VEC_SIZE, %esi
> -       jle     L(max)
> -
> -       VPCMPEQ (VEC_SIZE * 3)(%rdi), %ymm0, %ymm1
> -       vpmovmskb %ymm1, %eax
> +       VPCMPEQ %ymm2, %ymm0, %ymm2
> +       vpmovmskb       %ymm2, %eax
>         testl   %eax, %eax
> -
> -       jnz     L(first_vec_x3_check)
> -       movq    %r8, %rax
> -#  ifdef USE_AS_WCSLEN
> +       jnz     L(last_vec_return_x1)
> +
> +       /* Combine last 2 VEC.  */
> +       VPCMPEQ %ymm3, %ymm0, %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 - 1), %rdi
> +       addq    %rdi, %rax
> +# ifdef USE_AS_WCSLEN
>         shrq    $2, %rax
> -#  endif
> +# endif
>         VZEROUPPER_RETURN
>
> +
> +# ifdef USE_AS_STRNLEN
>         .p2align 4
> -L(last_2x_vec):
> -       addl    $(VEC_SIZE * 2), %esi
> -       VPCMPEQ (%rdi), %ymm0, %ymm1
> -       vpmovmskb %ymm1, %eax
> -       testl   %eax, %eax
> +L(last_4x_vec_or_less_load):
> +       /* Depending on entry adjust rdi / prepare first VEC in ymm1.  */
> +       subq    $-(VEC_SIZE * 4), %rdi
> +L(last_4x_vec_or_less_cmpeq):
> +       VPCMPEQ 1(%rdi), %ymm0, %ymm1
> +L(last_4x_vec_or_less):
>
> -       jnz     L(first_vec_x0_check)
> -       subl    $VEC_SIZE, %esi
> -       jle     L(max)
> +       vpmovmskb       %ymm1, %eax
> +       /* If remaining length > VEC_SIZE * 2.  */
> +       testl   $(VEC_SIZE * 2), %esi
> +       jnz     L(last_4x_vec)
>
> -       VPCMPEQ VEC_SIZE(%rdi), %ymm0, %ymm1
> -       vpmovmskb %ymm1, %eax
> +       /* length may have been negative or positive depending on where
> +          this was called from. This fixes that.  */
> +       andl    $(VEC_SIZE * 4 - 1), %esi
>         testl   %eax, %eax
> -       jnz     L(first_vec_x1_check)
> -       movq    %r8, %rax
> -#  ifdef USE_AS_WCSLEN
> -       shrq    $2, %rax
> -#  endif
> -       VZEROUPPER_RETURN
> +       jnz     L(last_vec_x1_check)
>
> -       .p2align 4
> -L(first_vec_x0_check):
> +       subl    $VEC_SIZE, %esi
> +       jb      L(max)
> +
> +       VPCMPEQ (VEC_SIZE + 1)(%rdi), %ymm0, %ymm1
> +       vpmovmskb       %ymm1, %eax
>         tzcntl  %eax, %eax
>         /* Check the end of data.  */
> -       cmpq    %rax, %rsi
> -       jbe     L(max)
> +       cmpl    %eax, %esi
> +       jb      L(max)
> +       subq    %rdx, %rdi
> +       addl    $(VEC_SIZE + 1), %eax
>         addq    %rdi, %rax
> -       subq    %rdx, %rax
>  #  ifdef USE_AS_WCSLEN
>         shrq    $2, %rax
>  #  endif
>         VZEROUPPER_RETURN
> +# endif
>
>         .p2align 4
> -L(first_vec_x1_check):
> +L(last_vec_return_x0):
>         tzcntl  %eax, %eax
> -       /* Check the end of data.  */
> -       cmpq    %rax, %rsi
> -       jbe     L(max)
> -       addq    $VEC_SIZE, %rax
> +       subq    $(VEC_SIZE * 4 - 1), %rdi
>         addq    %rdi, %rax
> -       subq    %rdx, %rax
> -#  ifdef USE_AS_WCSLEN
> +# ifdef USE_AS_WCSLEN
>         shrq    $2, %rax
> -#  endif
> +# endif
>         VZEROUPPER_RETURN
>
>         .p2align 4
> -L(first_vec_x2_check):
> +L(last_vec_return_x1):
>         tzcntl  %eax, %eax
> -       /* Check the end of data.  */
> -       cmpq    %rax, %rsi
> -       jbe     L(max)
> -       addq    $(VEC_SIZE * 2), %rax
> +       subq    $(VEC_SIZE * 3 - 1), %rdi
>         addq    %rdi, %rax
> -       subq    %rdx, %rax
> -#  ifdef USE_AS_WCSLEN
> +# ifdef USE_AS_WCSLEN
>         shrq    $2, %rax
> -#  endif
> +# endif
>         VZEROUPPER_RETURN
>
> +# ifdef USE_AS_STRNLEN
>         .p2align 4
> -L(first_vec_x3_check):
> +L(last_vec_x1_check):
> +
>         tzcntl  %eax, %eax
>         /* Check the end of data.  */
> -       cmpq    %rax, %rsi
> -       jbe     L(max)
> -       addq    $(VEC_SIZE * 3), %rax
> +       cmpl    %eax, %esi
> +       jb      L(max)
> +       subq    %rdx, %rdi
> +       incl    %eax
>         addq    %rdi, %rax
> -       subq    %rdx, %rax
>  #  ifdef USE_AS_WCSLEN
>         shrq    $2, %rax
>  #  endif
>         VZEROUPPER_RETURN
>
> -       .p2align 4
>  L(max):
>         movq    %r8, %rax
> +       VZEROUPPER_RETURN
> +
> +       .p2align 4
> +L(last_4x_vec):
> +       /* Test first 2x VEC normally.  */
> +       testl   %eax, %eax
> +       jnz     L(last_vec_x1)
> +
> +       VPCMPEQ (VEC_SIZE + 1)(%rdi), %ymm0, %ymm1
> +       vpmovmskb       %ymm1, %eax
> +       testl   %eax, %eax
> +       jnz     L(last_vec_x2)
> +
> +       /* Normalize length.  */
> +       andl    $(VEC_SIZE * 4 - 1), %esi
> +       VPCMPEQ (VEC_SIZE * 2 + 1)(%rdi), %ymm0, %ymm1
> +       vpmovmskb       %ymm1, %eax
> +       testl   %eax, %eax
> +       jnz     L(last_vec_x3)
> +
> +       subl    $(VEC_SIZE * 3), %esi
> +       jb      L(max)
> +
> +       VPCMPEQ (VEC_SIZE * 3 + 1)(%rdi), %ymm0, %ymm1
> +       vpmovmskb       %ymm1, %eax
> +       tzcntl  %eax, %eax
> +       /* Check the end of data.  */
> +       cmpl    %eax, %esi
> +       jb      L(max)
> +       subq    %rdx, %rdi
> +       addl    $(VEC_SIZE * 3 + 1), %eax
> +       addq    %rdi, %rax
>  #  ifdef USE_AS_WCSLEN
>         shrq    $2, %rax
>  #  endif
>         VZEROUPPER_RETURN
>
> -       .p2align 4
> -L(zero):
> -       xorl    %eax, %eax
> -       ret
> -# endif
>
>         .p2align 4
> -L(first_vec_x0):
> +L(last_vec_x1):
> +       /* essentially duplicates of first_vec_x1 but use 64 bit
> +          instructions.  */
>         tzcntl  %eax, %eax
> +       subq    %rdx, %rdi
> +       incl    %eax
>         addq    %rdi, %rax
> -       subq    %rdx, %rax
> -# ifdef USE_AS_WCSLEN
> +#  ifdef USE_AS_WCSLEN
>         shrq    $2, %rax
> -# endif
> +#  endif
>         VZEROUPPER_RETURN
>
>         .p2align 4
> -L(first_vec_x1):
> +L(last_vec_x2):
> +       /* essentially duplicates of first_vec_x1 but use 64 bit
> +          instructions.  */
>         tzcntl  %eax, %eax
> -       addq    $VEC_SIZE, %rax
> +       subq    %rdx, %rdi
> +       addl    $(VEC_SIZE + 1), %eax
>         addq    %rdi, %rax
> -       subq    %rdx, %rax
> -# ifdef USE_AS_WCSLEN
> +#  ifdef USE_AS_WCSLEN
>         shrq    $2, %rax
> -# endif
> +#  endif
>         VZEROUPPER_RETURN
>
>         .p2align 4
> -L(first_vec_x2):
> +L(last_vec_x3):
>         tzcntl  %eax, %eax
> -       addq    $(VEC_SIZE * 2), %rax
> +       subl    $(VEC_SIZE * 2), %esi
> +       /* Check the end of data.  */
> +       cmpl    %eax, %esi
> +       jb      L(max_end)
> +       subq    %rdx, %rdi
> +       addl    $(VEC_SIZE * 2 + 1), %eax
>         addq    %rdi, %rax
> -       subq    %rdx, %rax
> -# ifdef USE_AS_WCSLEN
> +#  ifdef USE_AS_WCSLEN
>         shrq    $2, %rax
> -# endif
> +#  endif
> +       VZEROUPPER_RETURN
> +L(max_end):
> +       movq    %r8, %rax
>         VZEROUPPER_RETURN
> +# endif
>
> +       /* Cold case for crossing page with first load.  */
>         .p2align 4
> -L(4x_vec_end):
> -       VPCMPEQ %ymm1, %ymm0, %ymm1
> -       vpmovmskb %ymm1, %eax
> -       testl   %eax, %eax
> -       jnz     L(first_vec_x0)
> -       VPCMPEQ %ymm2, %ymm0, %ymm2
> -       vpmovmskb %ymm2, %eax
> +L(cross_page_boundary):
> +       /* Align data to VEC_SIZE - 1.  */
> +       orq     $(VEC_SIZE - 1), %rdi
> +       VPCMPEQ -(VEC_SIZE - 1)(%rdi), %ymm0, %ymm1
> +       vpmovmskb       %ymm1, %eax
> +       /* Remove the leading bytes.  */
> +       sarxl   %edx, %eax, %eax
> +# ifdef USE_AS_STRNLEN
>         testl   %eax, %eax
> -       jnz     L(first_vec_x1)
> -       VPCMPEQ %ymm3, %ymm0, %ymm3
> -       vpmovmskb %ymm3, %eax
> +       jnz     L(cross_page_less_vec)
> +       leaq    1(%rdi), %rcx
> +       subq    %rdx, %rcx
> +       /* Check length.  */
> +       cmpq    %rsi, %rcx
> +       jb      L(cross_page_continue)
> +       movq    %r8, %rax
> +# else
>         testl   %eax, %eax
> -       jnz     L(first_vec_x2)
> -       VPCMPEQ %ymm4, %ymm0, %ymm4
> -       vpmovmskb %ymm4, %eax
> -L(first_vec_x3):
> +       jz      L(cross_page_continue)
>         tzcntl  %eax, %eax
> -       addq    $(VEC_SIZE * 3), %rax
> -       addq    %rdi, %rax
> -       subq    %rdx, %rax
> -# ifdef USE_AS_WCSLEN
> -       shrq    $2, %rax
> +#  ifdef USE_AS_WCSLEN
> +       shrl    $2, %eax
> +#  endif
>  # endif
> +# ifdef USE_IN_RTM

Remove this.

> +L(return_vzeroupper):
> +       ZERO_UPPER_VEC_REGISTERS_RETURN
> +# else
> +       VZEROUPPER_RETURN
> +# endif

Remove the 3 lines above.

> +
> +# ifdef USE_AS_STRNLEN
> +       .p2align 4
> +L(cross_page_less_vec):
> +       tzcntl  %eax, %eax
> +       cmpq    %rax, %rsi
> +       cmovb   %esi, %eax
> +#  ifdef USE_AS_WCSLEN
> +       shrl    $2, %eax
> +#  endif
>         VZEROUPPER_RETURN
> +# endif
>
>  END (STRLEN)
>  #endif
> --
> 2.29.2
>

Thanks.