[v3,3/3] x86: Optimize memchr-evex.S

  No bug. This commit optimizes memchr-evex.S. The optimizations include
replacing some branches with cmovcc, avoiding some branches entirely
in the less_4x_vec case, making the page cross logic less strict,
saving some ALU in the alignment process, and most importantly
increasing ILP in the 4x loop. test-memchr, test-rawmemchr, and
test-wmemchr are all passing.

Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
---
 sysdeps/x86_64/multiarch/memchr-evex.S | 547 +++++++++++++++----------
 1 file changed, 322 insertions(+), 225 deletions(-)
  

On Mon, May 3, 2021 at 6:58 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> No bug. This commit optimizes memchr-evex.S. The optimizations include
> replacing some branches with cmovcc, avoiding some branches entirely
> in the less_4x_vec case, making the page cross logic less strict,
> saving some ALU in the alignment process, and most importantly
> increasing ILP in the 4x loop. test-memchr, test-rawmemchr, and
> test-wmemchr are all passing.
>
> Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
> ---
>  sysdeps/x86_64/multiarch/memchr-evex.S | 547 +++++++++++++++----------
>  1 file changed, 322 insertions(+), 225 deletions(-)
>
> diff --git a/sysdeps/x86_64/multiarch/memchr-evex.S b/sysdeps/x86_64/multiarch/memchr-evex.S
> index 6dd5d67b90..81d5cd6486 100644
> --- a/sysdeps/x86_64/multiarch/memchr-evex.S
> +++ b/sysdeps/x86_64/multiarch/memchr-evex.S
> @@ -26,14 +26,28 @@
>
>  # ifdef USE_AS_WMEMCHR
>  #  define VPBROADCAST  vpbroadcastd
> -#  define VPCMP                vpcmpd
> -#  define SHIFT_REG    r8d
> +#  define VPMINU       vpminud
> +#  define VPCMP        vpcmpd
> +#  define VPCMPEQ      vpcmpeqd
> +#  define CHAR_SIZE    4
>  # else
>  #  define VPBROADCAST  vpbroadcastb
> -#  define VPCMP                vpcmpb
> -#  define SHIFT_REG    ecx
> +#  define VPMINU       vpminub
> +#  define VPCMP        vpcmpb
> +#  define VPCMPEQ      vpcmpeqb
> +#  define CHAR_SIZE    1
>  # endif
>
> +# ifdef USE_AS_RAWMEMCHR
> +#  define RAW_PTR_REG  rcx
> +#  define ALGN_PTR_REG rdi
> +# else
> +#  define RAW_PTR_REG  rdi
> +#  define ALGN_PTR_REG rcx
> +# endif
> +
> +# define XMMZERO       xmm23
> +# define YMMZERO       ymm23
>  # define XMMMATCH      xmm16
>  # define YMMMATCH      ymm16
>  # define YMM1          ymm17
> @@ -44,6 +58,8 @@
>  # define YMM6          ymm22
>
>  # define VEC_SIZE 32
> +# define CHAR_PER_VEC (VEC_SIZE / CHAR_SIZE)
> +# define PAGE_SIZE 4096
>
>         .section .text.evex,"ax",@progbits
>  ENTRY (MEMCHR)
> @@ -51,11 +67,7 @@ ENTRY (MEMCHR)
>         /* Check for zero length.  */
>         test    %RDX_LP, %RDX_LP
>         jz      L(zero)
> -# endif
> -       movl    %edi, %ecx
> -# ifdef USE_AS_WMEMCHR
> -       shl     $2, %RDX_LP
> -# else
> +
>  #  ifdef __ILP32__
>         /* Clear the upper 32 bits.  */
>         movl    %edx, %edx
> @@ -64,318 +76,403 @@ ENTRY (MEMCHR)
>         /* Broadcast CHAR to YMMMATCH.  */
>         VPBROADCAST %esi, %YMMMATCH
>         /* 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)
> +       movl    %edi, %eax
> +       andl    $(PAGE_SIZE - 1), %eax
> +       cmpl    $(PAGE_SIZE - VEC_SIZE), %eax
> +       ja      L(cross_page_boundary)
>
>         /* Check the first VEC_SIZE bytes.  */
> -       VPCMP   $0, (%rdi), %YMMMATCH, %k1
> -       kmovd   %k1, %eax
> -       testl   %eax, %eax
> -
> +       VPCMP   $0, (%rdi), %YMMMATCH, %k0
> +       kmovd   %k0, %eax
>  # ifndef USE_AS_RAWMEMCHR
> -       jnz     L(first_vec_x0_check)
> -       /* Adjust length and check the end of data.  */
> -       subq    $VEC_SIZE, %rdx
> -       jbe     L(zero)
> +       /* If length < CHAR_PER_VEC handle special.  */
> +       cmpq    $CHAR_PER_VEC, %rdx
> +       jbe     L(first_vec_x0)
> +# endif
> +       testl   %eax, %eax
> +       jz      L(aligned_more)
> +       tzcntl  %eax, %eax
> +# ifdef USE_AS_WMEMCHR
> +       /* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count.  */
> +       leaq    (%rdi, %rax, CHAR_SIZE), %rax
>  # else
> -       jnz     L(first_vec_x0)
> +       addq    %rdi, %rax
>  # endif
> -
> -       /* Align data for aligned loads in the loop.  */
> -       addq    $VEC_SIZE, %rdi
> -       andl    $(VEC_SIZE - 1), %ecx
> -       andq    $-VEC_SIZE, %rdi
> +       ret
>
>  # ifndef USE_AS_RAWMEMCHR
> -       /* Adjust length.  */
> -       addq    %rcx, %rdx
> -
> -       subq    $(VEC_SIZE * 4), %rdx
> -       jbe     L(last_4x_vec_or_less)
> -# endif
> -       jmp     L(more_4x_vec)
> +L(zero):
> +       xorl    %eax, %eax
> +       ret
>
> +       .p2align 5
> +L(first_vec_x0):
> +       /* Check if first match was before length.  */
> +       tzcntl  %eax, %eax
> +       xorl    %ecx, %ecx
> +       cmpl    %eax, %edx
> +       leaq    (%rdi, %rax, CHAR_SIZE), %rax
> +       cmovle  %rcx, %rax
> +       ret
> +# else
> +       /* NB: first_vec_x0 is 17 bytes which will leave
> +          cross_page_boundary (which is relatively cold) close enough
> +          to ideal alignment. So only realign L(cross_page_boundary) if
> +          rawmemchr.  */
>         .p2align 4
> -L(cros_page_boundary):
> -       andl    $(VEC_SIZE - 1), %ecx
> +# endif
> +L(cross_page_boundary):
> +       /* Save pointer before aligning as its original value is
> +          necessary for computer return address if byte is found or
> +          adjusting length if it is not and this is memchr.  */
> +       movq    %rdi, %rcx
> +       /* Align data to VEC_SIZE. ALGN_PTR_REG is rcx for memchr and rdi
> +          for rawmemchr.  */
> +       andq    $-VEC_SIZE, %ALGN_PTR_REG
> +       VPCMP   $0, (%ALGN_PTR_REG), %YMMMATCH, %k0
> +       kmovd   %k0, %r8d
>  # ifdef USE_AS_WMEMCHR
> -       /* NB: Divide shift count by 4 since each bit in K1 represent 4
> +       /* NB: Divide shift count by 4 since each bit in K0 represent 4
>            bytes.  */
> -       movl    %ecx, %SHIFT_REG
> -       sarl    $2, %SHIFT_REG
> +       sarl    $2, %eax
> +# endif
> +# ifndef USE_AS_RAWMEMCHR
> +       movl    $(PAGE_SIZE / CHAR_SIZE), %esi
> +       subl    %eax, %esi
>  # endif
> -       andq    $-VEC_SIZE, %rdi
> -       VPCMP   $0, (%rdi), %YMMMATCH, %k1
> -       kmovd   %k1, %eax
> -       /* Remove the leading bytes.  */
> -       sarxl   %SHIFT_REG, %eax, %eax
> -       testl   %eax, %eax
> -       jz      L(aligned_more)
> -       tzcntl  %eax, %eax
>  # ifdef USE_AS_WMEMCHR
> -       /* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> -       sall    $2, %eax
> +       andl    $(CHAR_PER_VEC - 1), %eax
>  # endif
> +       /* Remove the leading bytes.  */
> +       sarxl   %eax, %r8d, %eax
>  # ifndef USE_AS_RAWMEMCHR
>         /* Check the end of data.  */
> -       cmpq    %rax, %rdx
> -       jbe     L(zero)
> +       cmpq    %rsi, %rdx
> +       jbe     L(first_vec_x0)
> +# endif
> +       testl   %eax, %eax
> +       jz      L(cross_page_continue)
> +       tzcntl  %eax, %eax
> +# ifdef USE_AS_WMEMCHR
> +       /* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count.  */
> +       leaq    (%RAW_PTR_REG, %rax, CHAR_SIZE), %rax
> +# else
> +       addq    %RAW_PTR_REG, %rax
>  # endif
> -       addq    %rdi, %rax
> -       addq    %rcx, %rax
>         ret
>
>         .p2align 4
> -L(aligned_more):
> -# ifndef USE_AS_RAWMEMCHR
> -        /* 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
> +L(first_vec_x1):
> +       tzcntl  %eax, %eax
> +       leaq    VEC_SIZE(%rdi, %rax, CHAR_SIZE), %rax
> +       ret
>
> -       /* Check the end of data.  */
> -       subq    %rcx, %rdx
> -       jbe     L(zero)
> -# endif
> +       .p2align 4
> +L(first_vec_x2):
> +       tzcntl  %eax, %eax
> +       leaq    (VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %rax
> +       ret
>
> -       addq    $VEC_SIZE, %rdi
> +       .p2align 4
> +L(first_vec_x3):
> +       tzcntl  %eax, %eax
> +       leaq    (VEC_SIZE * 3)(%rdi, %rax, CHAR_SIZE), %rax
> +       ret
>
> -# ifndef USE_AS_RAWMEMCHR
> -       subq    $(VEC_SIZE * 4), %rdx
> -       jbe     L(last_4x_vec_or_less)
> -# endif
> +       .p2align 4
> +L(first_vec_x4):
> +       tzcntl  %eax, %eax
> +       leaq    (VEC_SIZE * 4)(%rdi, %rax, CHAR_SIZE), %rax
> +       ret
>
> -L(more_4x_vec):
> +       .p2align 5
> +L(aligned_more):
>         /* Check the first 4 * VEC_SIZE.  Only one VEC_SIZE at a time
>            since data is only aligned to VEC_SIZE.  */
> -       VPCMP   $0, (%rdi), %YMMMATCH, %k1
> -       kmovd   %k1, %eax
> -       testl   %eax, %eax
> -       jnz     L(first_vec_x0)
>
> -       VPCMP   $0, VEC_SIZE(%rdi), %YMMMATCH, %k1
> -       kmovd   %k1, %eax
> +# ifndef USE_AS_RAWMEMCHR
> +       /* Align data to VEC_SIZE.  */
> +L(cross_page_continue):
> +       xorl    %ecx, %ecx
> +       subl    %edi, %ecx
> +       andq    $-VEC_SIZE, %rdi
> +       /* esi is for adjusting length to see if near the end.  */
> +       leal    (VEC_SIZE * 5)(%rdi, %rcx), %esi
> +#  ifdef USE_AS_WMEMCHR
> +       /* NB: Divide bytes by 4 to get the wchar_t count.  */
> +       sarl    $2, %esi
> +#  endif
> +# else
> +       andq    $-VEC_SIZE, %rdi
> +L(cross_page_continue):
> +# endif
> +       /* Load first VEC regardless.  */
> +       VPCMP   $0, (VEC_SIZE)(%rdi), %YMMMATCH, %k0
> +       kmovd   %k0, %eax
> +# ifndef USE_AS_RAWMEMCHR
> +       /* Adjust length. If near end handle specially.  */
> +       subq    %rsi, %rdx
> +       jbe     L(last_4x_vec_or_less)
> +# endif
>         testl   %eax, %eax
>         jnz     L(first_vec_x1)
>
> -       VPCMP   $0, (VEC_SIZE * 2)(%rdi), %YMMMATCH, %k1
> -       kmovd   %k1, %eax
> +       VPCMP   $0, (VEC_SIZE * 2)(%rdi), %YMMMATCH, %k0
> +       kmovd   %k0, %eax
>         testl   %eax, %eax
>         jnz     L(first_vec_x2)
>
> -       VPCMP   $0, (VEC_SIZE * 3)(%rdi), %YMMMATCH, %k1
> -       kmovd   %k1, %eax
> +       VPCMP   $0, (VEC_SIZE * 3)(%rdi), %YMMMATCH, %k0
> +       kmovd   %k0, %eax
>         testl   %eax, %eax
>         jnz     L(first_vec_x3)
>
> -       addq    $(VEC_SIZE * 4), %rdi
> +       VPCMP   $0, (VEC_SIZE * 4)(%rdi), %YMMMATCH, %k0
> +       kmovd   %k0, %eax
> +       testl   %eax, %eax
> +       jnz     L(first_vec_x4)
> +
>
>  # ifndef USE_AS_RAWMEMCHR
> -       subq    $(VEC_SIZE * 4), %rdx
> -       jbe     L(last_4x_vec_or_less)
> -# endif
> +       /* Check if at last CHAR_PER_VEC * 4 length.  */
> +       subq    $(CHAR_PER_VEC * 4), %rdx
> +       jbe     L(last_4x_vec_or_less_cmpeq)
> +       addq    $VEC_SIZE, %rdi
>
> -       /* Align data to 4 * VEC_SIZE.  */
> -       movq    %rdi, %rcx
> -       andl    $(4 * VEC_SIZE - 1), %ecx
> +       /* Align data to VEC_SIZE * 4 for the loop and readjust length.
> +        */
> +#  ifdef USE_AS_WMEMCHR
> +       movl    %edi, %ecx
>         andq    $-(4 * VEC_SIZE), %rdi
> -
> -# ifndef USE_AS_RAWMEMCHR
> -       /* Adjust length.  */
> +       andl    $(VEC_SIZE * 4 - 1), %ecx
> +       /* NB: Divide bytes by 4 to get the wchar_t count.  */
> +       sarl    $2, %ecx
>         addq    %rcx, %rdx
> +#  else
> +       addq    %rdi, %rdx
> +       andq    $-(4 * VEC_SIZE), %rdi
> +       subq    %rdi, %rdx
> +#  endif
> +# else
> +       addq    $VEC_SIZE, %rdi
> +       andq    $-(4 * VEC_SIZE), %rdi
>  # endif
>
> +       vpxorq  %XMMZERO, %XMMZERO, %XMMZERO
> +
> +       /* Compare 4 * VEC at a time forward.  */
>         .p2align 4
>  L(loop_4x_vec):
> -       /* Compare 4 * VEC at a time forward.  */
> -       VPCMP   $0, (%rdi), %YMMMATCH, %k1
> -       VPCMP   $0, VEC_SIZE(%rdi), %YMMMATCH, %k2
> -       kord    %k1, %k2, %k5
> -       VPCMP   $0, (VEC_SIZE * 2)(%rdi), %YMMMATCH, %k3
> -       VPCMP   $0, (VEC_SIZE * 3)(%rdi), %YMMMATCH, %k4
> -
> -       kord    %k3, %k4, %k6
> -       kortestd %k5, %k6
> -       jnz     L(4x_vec_end)
> -
> -       addq    $(VEC_SIZE * 4), %rdi
> -
> +       /* It would be possible to save some instructions using 4x VPCMP
> +          but bottleneck on port 5 makes it not woth it.  */
> +       VPCMP   $4, (VEC_SIZE * 4)(%rdi), %YMMMATCH, %k1
> +       /* xor will set bytes match esi to zero.  */
> +       vpxorq  (VEC_SIZE * 5)(%rdi), %YMMMATCH, %YMM2
> +       vpxorq  (VEC_SIZE * 6)(%rdi), %YMMMATCH, %YMM3
> +       VPCMP   $0, (VEC_SIZE * 7)(%rdi), %YMMMATCH, %k3
> +       /* Reduce VEC2 / VEC3 with min and VEC1 with zero mask.  */
> +       VPMINU  %YMM2, %YMM3, %YMM3 {%k1} {z}
> +       VPCMP   $0, %YMM3, %YMMZERO, %k2
>  # ifdef USE_AS_RAWMEMCHR
> -       jmp     L(loop_4x_vec)
> +       subq    $-(VEC_SIZE * 4), %rdi
> +       kortestd %k2, %k3
> +       jz      L(loop_4x_vec)
>  # else
> -       subq    $(VEC_SIZE * 4), %rdx
> +       kortestd %k2, %k3
> +       jnz     L(loop_4x_vec_end)
> +
> +       subq    $-(VEC_SIZE * 4), %rdi
> +
> +       subq    $(CHAR_PER_VEC * 4), %rdx
>         ja      L(loop_4x_vec)
>
> +       /* Fall through into less than 4 remaining vectors of length case.
> +        */
> +       VPCMP   $0, (VEC_SIZE * 4)(%rdi), %YMMMATCH, %k0
> +       kmovd   %k0, %eax
> +       addq    $(VEC_SIZE * 3), %rdi
> +       .p2align 4
>  L(last_4x_vec_or_less):
> -       /* Less than 4 * VEC and aligned to VEC_SIZE.  */
> -       addl    $(VEC_SIZE * 2), %edx
> -       jle     L(last_2x_vec)
> -
> -       VPCMP   $0, (%rdi), %YMMMATCH, %k1
> -       kmovd   %k1, %eax
> +       /* Check if first VEC contained match.  */
>         testl   %eax, %eax
> -       jnz     L(first_vec_x0)
> +       jnz     L(first_vec_x1_check)
>
> -       VPCMP   $0, VEC_SIZE(%rdi), %YMMMATCH, %k1
> -       kmovd   %k1, %eax
> -       testl   %eax, %eax
> -       jnz     L(first_vec_x1)
> +       /* If remaining length > CHAR_PER_VEC * 2.  */
> +       addl    $(CHAR_PER_VEC * 2), %edx
> +       jg      L(last_4x_vec)
>
> -       VPCMP   $0, (VEC_SIZE * 2)(%rdi), %YMMMATCH, %k1
> -       kmovd   %k1, %eax
> -       testl   %eax, %eax
> +L(last_2x_vec):
> +       /* If remaining length < CHAR_PER_VEC.  */
> +       addl    $CHAR_PER_VEC, %edx
> +       jle     L(zero_end)
>
> -       jnz     L(first_vec_x2_check)
> -       subl    $VEC_SIZE, %edx
> -       jle     L(zero)
> +       /* Check VEC2 and compare any match with remaining length.  */
> +       VPCMP   $0, (VEC_SIZE * 2)(%rdi), %YMMMATCH, %k0
> +       kmovd   %k0, %eax
> +       tzcntl  %eax, %eax
> +       cmpl    %eax, %edx
> +       jbe     L(set_zero_end)
> +       leaq    (VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %rax
> +L(zero_end):
> +       ret
>
> -       VPCMP   $0, (VEC_SIZE * 3)(%rdi), %YMMMATCH, %k1
> -       kmovd   %k1, %eax
> -       testl   %eax, %eax
>
> -       jnz     L(first_vec_x3_check)
> +       .p2align 4
> +L(first_vec_x1_check):
> +       tzcntl  %eax, %eax
> +       /* Adjust length.  */
> +       subl    $-(CHAR_PER_VEC * 4), %edx
> +       /* Check if match within remaining length.  */
> +       cmpl    %eax, %edx
> +       jbe     L(set_zero_end)
> +       /* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count.  */
> +       leaq    VEC_SIZE(%rdi, %rax, CHAR_SIZE), %rax
> +       ret
> +L(set_zero_end):
>         xorl    %eax, %eax
>         ret
>
>         .p2align 4
> -L(last_2x_vec):
> -       addl    $(VEC_SIZE * 2), %edx
> -       VPCMP   $0, (%rdi), %YMMMATCH, %k1
> +L(loop_4x_vec_end):
> +# endif
> +       /* rawmemchr will fall through into this if match was found in
> +          loop.  */
> +
> +       /* k1 has not of matches with VEC1.  */
>         kmovd   %k1, %eax
> -       testl   %eax, %eax
> +# ifdef USE_AS_WMEMCHR
> +       subl    $((1 << CHAR_PER_VEC) - 1), %eax
> +# else
> +       incl    %eax
> +# endif
> +       jnz     L(last_vec_x1_return)
>
> -       jnz     L(first_vec_x0_check)
> -       subl    $VEC_SIZE, %edx
> -       jle     L(zero)
> +       VPCMP   $0, %YMM2, %YMMZERO, %k0
> +       kmovd   %k0, %eax
> +       testl   %eax, %eax
> +       jnz     L(last_vec_x2_return)
>
> -       VPCMP   $0, VEC_SIZE(%rdi), %YMMMATCH, %k1
> -       kmovd   %k1, %eax
> +       kmovd   %k2, %eax
>         testl   %eax, %eax
> -       jnz     L(first_vec_x1_check)
> -       xorl    %eax, %eax
> -       ret
> +       jnz     L(last_vec_x3_return)
>
> -       .p2align 4
> -L(first_vec_x0_check):
> +       kmovd   %k3, %eax
>         tzcntl  %eax, %eax
> -# ifdef USE_AS_WMEMCHR
> -       /* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> -       sall    $2, %eax
> +# ifdef USE_AS_RAWMEMCHR
> +       leaq    (VEC_SIZE * 3)(%rdi, %rax, CHAR_SIZE), %rax
> +# else
> +       leaq    (VEC_SIZE * 7)(%rdi, %rax, CHAR_SIZE), %rax
>  # endif
> -       /* Check the end of data.  */
> -       cmpq    %rax, %rdx
> -       jbe     L(zero)
> -       addq    %rdi, %rax
>         ret
>
>         .p2align 4
> -L(first_vec_x1_check):
> +L(last_vec_x1_return):
>         tzcntl  %eax, %eax
> -# ifdef USE_AS_WMEMCHR
> -       /* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> -       sall    $2, %eax
> -# endif
> -       /* Check the end of data.  */
> -       cmpq    %rax, %rdx
> -       jbe     L(zero)
> -       addq    $VEC_SIZE, %rax
> +# ifdef USE_AS_RAWMEMCHR
> +#  ifdef USE_AS_WMEMCHR
> +       /* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count.  */
> +       leaq    (%rdi, %rax, CHAR_SIZE), %rax
> +#  else
>         addq    %rdi, %rax
> -       ret
> -
> -       .p2align 4
> -L(first_vec_x2_check):
> -       tzcntl  %eax, %eax
> -# ifdef USE_AS_WMEMCHR
> -       /* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> -       sall    $2, %eax
> +#  endif
> +# else
> +       /* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count.  */
> +       leaq    (VEC_SIZE * 4)(%rdi, %rax, CHAR_SIZE), %rax
>  # endif
> -       /* Check the end of data.  */
> -       cmpq    %rax, %rdx
> -       jbe     L(zero)
> -       addq    $(VEC_SIZE * 2), %rax
> -       addq    %rdi, %rax
>         ret
>
>         .p2align 4
> -L(first_vec_x3_check):
> +L(last_vec_x2_return):
>         tzcntl  %eax, %eax
> -# ifdef USE_AS_WMEMCHR
> -       /* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> -       sall    $2, %eax
> +# ifdef USE_AS_RAWMEMCHR
> +       /* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count.  */
> +       leaq    VEC_SIZE(%rdi, %rax, CHAR_SIZE), %rax
> +# else
> +       /* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count.  */
> +       leaq    (VEC_SIZE * 5)(%rdi, %rax, CHAR_SIZE), %rax
>  # endif
> -       /* Check the end of data.  */
> -       cmpq    %rax, %rdx
> -       jbe     L(zero)
> -       addq    $(VEC_SIZE * 3), %rax
> -       addq    %rdi, %rax
>         ret
>
>         .p2align 4
> -L(zero):
> -       xorl    %eax, %eax
> -       ret
> -# endif
> -
> -       .p2align 4
> -L(first_vec_x0):
> +L(last_vec_x3_return):
>         tzcntl  %eax, %eax
> -# ifdef USE_AS_WMEMCHR
> -       /* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> -       leaq    (%rdi, %rax, 4), %rax
> +# ifdef USE_AS_RAWMEMCHR
> +       /* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count.  */
> +       leaq    (VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %rax
>  # else
> -       addq    %rdi, %rax
> +       /* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count.  */
> +       leaq    (VEC_SIZE * 6)(%rdi, %rax, CHAR_SIZE), %rax
>  # endif
>         ret
>
> +
> +# ifndef USE_AS_RAWMEMCHR
> +L(last_4x_vec_or_less_cmpeq):
> +       VPCMP   $0, (VEC_SIZE * 5)(%rdi), %YMMMATCH, %k0
> +       kmovd   %k0, %eax
> +       subq    $-(VEC_SIZE * 4), %rdi
> +       /* Check first VEC regardless.  */
> +       testl   %eax, %eax
> +       jnz     L(first_vec_x1_check)
> +
> +       /* If remaining length <= CHAR_PER_VEC * 2.  */
> +       addl    $(CHAR_PER_VEC * 2), %edx
> +       jle     L(last_2x_vec)
> +
>         .p2align 4
> -L(first_vec_x1):
> +L(last_4x_vec):
> +       VPCMP   $0, (VEC_SIZE * 2)(%rdi), %YMMMATCH, %k0
> +       kmovd   %k0, %eax
> +       testl   %eax, %eax
> +       jnz     L(last_vec_x2)
> +
> +
> +       VPCMP   $0, (VEC_SIZE * 3)(%rdi), %YMMMATCH, %k0
> +       kmovd   %k0, %eax
> +       /* Create mask for possible matches within remaining length.  */
> +#  ifdef USE_AS_WMEMCHR
> +       movl    $((1 << (CHAR_PER_VEC * 2)) - 1), %ecx
> +       bzhil   %edx, %ecx, %ecx
> +#  else
> +       movq    $-1, %rcx
> +       bzhiq   %rdx, %rcx, %rcx
> +#  endif
> +       /* Test matches in data against length match.  */
> +       andl    %ecx, %eax
> +       jnz     L(last_vec_x3)
> +
> +       /* if remaining length <= CHAR_PER_VEC * 3 (Note this is after
> +          remaining length was found to be > CHAR_PER_VEC * 2.  */
> +       subl    $CHAR_PER_VEC, %edx
> +       jbe     L(zero_end2)
> +
> +
> +       VPCMP   $0, (VEC_SIZE * 4)(%rdi), %YMMMATCH, %k0
> +       kmovd   %k0, %eax
> +       /* Shift remaining length mask for last VEC.  */
> +#  ifdef USE_AS_WMEMCHR
> +       shrl    $CHAR_PER_VEC, %ecx
> +#  else
> +       shrq    $CHAR_PER_VEC, %rcx
> +#  endif
> +       andl    %ecx, %eax
> +       jz      L(zero_end2)
>         tzcntl  %eax, %eax
> -# ifdef USE_AS_WMEMCHR
> -       /* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> -       leaq    VEC_SIZE(%rdi, %rax, 4), %rax
> -# else
> -       addq    $VEC_SIZE, %rax
> -       addq    %rdi, %rax
> -# endif
> +       leaq    (VEC_SIZE * 4)(%rdi, %rax, CHAR_SIZE), %rax
> +L(zero_end2):
>         ret
>
> -       .p2align 4
> -L(first_vec_x2):
> +L(last_vec_x2):
>         tzcntl  %eax, %eax
> -# ifdef USE_AS_WMEMCHR
> -       /* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> -       leaq    (VEC_SIZE * 2)(%rdi, %rax, 4), %rax
> -# else
> -       addq    $(VEC_SIZE * 2), %rax
> -       addq    %rdi, %rax
> -# endif
> +       leaq    (VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %rax
>         ret
>
>         .p2align 4
> -L(4x_vec_end):
> -       kmovd   %k1, %eax
> -       testl   %eax, %eax
> -       jnz     L(first_vec_x0)
> -       kmovd   %k2, %eax
> -       testl   %eax, %eax
> -       jnz     L(first_vec_x1)
> -       kmovd   %k3, %eax
> -       testl   %eax, %eax
> -       jnz     L(first_vec_x2)
> -       kmovd   %k4, %eax
> -       testl   %eax, %eax
> -L(first_vec_x3):
> +L(last_vec_x3):
>         tzcntl  %eax, %eax
> -# ifdef USE_AS_WMEMCHR
> -       /* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> -       leaq    (VEC_SIZE * 3)(%rdi, %rax, 4), %rax
> -# else
> -       addq    $(VEC_SIZE * 3), %rax
> -       addq    %rdi, %rax
> -# endif
> +       leaq    (VEC_SIZE * 3)(%rdi, %rax, CHAR_SIZE), %rax
>         ret
> +# endif
>
>  END (MEMCHR)
>  #endif
> --
> 2.29.2
>

This is the patch I will push unless anyone has any objections.