diff mbox series

[v1,2/3] x86: Optimize memchr-avx2.S

Message ID 20210503084435.160548-2-goldstein.w.n@gmail.com
State Superseded
Headers show
Series [v1,1/3] Bench: Expand bench-memchr.c | expand

Commit Message

Noah Goldstein May 3, 2021, 8:44 a.m. UTC
No bug. This commit optimizes memchr-avx2.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,
asaving a few instructions the in loop return 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-avx2.S | 446 +++++++++++++++----------
 1 file changed, 262 insertions(+), 184 deletions(-)

Comments

H.J. Lu May 3, 2021, 6:50 p.m. UTC | #1
On Mon, May 03, 2021 at 04:44:36AM -0400, Noah Goldstein wrote:
> No bug. This commit optimizes memchr-avx2.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,
> asaving a few instructions the in loop return 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-avx2.S | 446 +++++++++++++++----------
>  1 file changed, 262 insertions(+), 184 deletions(-)
> 
> diff --git a/sysdeps/x86_64/multiarch/memchr-avx2.S b/sysdeps/x86_64/multiarch/memchr-avx2.S
> index 1fcb1c350f..8368fcd1e1 100644
> --- a/sysdeps/x86_64/multiarch/memchr-avx2.S
> +++ b/sysdeps/x86_64/multiarch/memchr-avx2.S
> @@ -26,8 +26,22 @@
>  
>  # ifdef USE_AS_WMEMCHR
>  #  define VPCMPEQ	vpcmpeqd
> +#  define VPBROADCAST	vpbroadcastd
> +#  define CHAR_SIZE	4
>  # else
>  #  define VPCMPEQ	vpcmpeqb
> +#  define VPBROADCAST	vpbroadcastb
> +#  define CHAR_SIZE	1
> +# endif
> +
> +# ifdef USE_AS_RAWMEMCHR
> +#  define ERAW_PTR_REG	ecx
> +#  define RRAW_PTR_REG	rcx
> +#  define ALGN_PTR_REG	rdi
> +# else
> +#  define ERAW_PTR_REG	edi
> +#  define RRAW_PTR_REG	rdi
> +#  define ALGN_PTR_REG	rcx
>  # endif
>  
>  # ifndef VZEROUPPER
> @@ -39,303 +53,367 @@
>  # endif
>  
>  # define VEC_SIZE 32
> +# define PAGE_SIZE 4096
> +

Remove the extra line here.

>  
>  	.section SECTION(.text),"ax",@progbits
> -ENTRY (MEMCHR)
> +ENTRY(MEMCHR)

No need for this change.

>  # ifndef USE_AS_RAWMEMCHR
>  	/* Check for zero length.  */
>  	test	%RDX_LP, %RDX_LP
>  	jz	L(null)
>  # endif
> -	movl	%edi, %ecx
> -	/* Broadcast CHAR to YMM0.  */
> -	vmovd	%esi, %xmm0
>  # ifdef USE_AS_WMEMCHR
>  	shl	$2, %RDX_LP
> -	vpbroadcastd %xmm0, %ymm0
>  # else
>  #  ifdef __ILP32__
>  	/* Clear the upper 32 bits.  */
>  	movl	%edx, %edx
>  #  endif
> -	vpbroadcastb %xmm0, %ymm0
>  # endif
> -	/* 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)
> +	/* Broadcast CHAR to YMMMATCH.  */
> +	vmovd	%esi, %xmm0
> +	VPBROADCAST %xmm0, %ymm0
> +	/* Check if we may cross page boundary with one
> +	   vector load.  */
> +	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.  */
> -	VPCMPEQ (%rdi), %ymm0, %ymm1
> +	VPCMPEQ	(%rdi), %ymm0, %ymm1
>  	vpmovmskb %ymm1, %eax
> -	testl	%eax, %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)
> -# else
> -	jnz	L(first_vec_x0)
> +	/* If length < CHAR_PER_VEC handle special.  */
> +	cmpq	$VEC_SIZE, %rdx
> +	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
> +	addq	%rdi, %rax
> +	VZEROUPPER_RETURN
>  
>  # ifndef USE_AS_RAWMEMCHR
> -	/* Adjust length.  */
> -	addq	%rcx, %rdx
> -
> -	subq	$(VEC_SIZE * 4), %rdx
> -	jbe	L(last_4x_vec_or_less)
> +	.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), %rax
> +	cmovle	%rcx, %rax
> +	VZEROUPPER_RETURN
> +L(null):
> +	xorl	%eax, %eax
> +	ret
>  # 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
> +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

Fit comments to 72 columns.

> +	   memchr.  */
> +	movq	%rdi, %rcx
> +	/* Align data to VEC_SIZE - 1. ALGN_PTR_REG is
> +	   rcx for memchr and rdi for rawmemchr.  */
> +	orq	$(VEC_SIZE - 1), %ALGN_PTR_REG
> +	VPCMPEQ	-(VEC_SIZE - 1)(%ALGN_PTR_REG), %ymm0, %ymm1
>  	vpmovmskb %ymm1, %eax
> +# ifndef USE_AS_RAWMEMCHR
> +	/* Calculate length until end of page (length
> +	   checked for a match).  */
> +	leaq	1(%ALGN_PTR_REG), %rsi
> +	subq	%RRAW_PTR_REG, %rsi
> +# endif
>  	/* Remove the leading bytes.  */
> -	sarl	%cl, %eax
> -	testl	%eax, %eax
> -	jz	L(aligned_more)
> -	tzcntl	%eax, %eax
> +	sarxl	%ERAW_PTR_REG, %eax, %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
> -	addq	%rdi, %rax
> -	addq	%rcx, %rax
> +	testl	%eax, %eax
> +	jz	L(cross_page_continue)
> +	tzcntl	%eax, %eax
> +	addq	%RRAW_PTR_REG, %rax
>  L(return_vzeroupper):
>  	ZERO_UPPER_VEC_REGISTERS_RETURN
>  
>  	.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
> +	incq	%rdi
> +	addq	%rdi, %rax
> +	VZEROUPPER_RETURN
>  
> -	/* Check the end of data.  */
> -	subq	%rcx, %rdx
> -	jbe	L(zero)
> -# endif
> +	.p2align 4
> +L(first_vec_x2):
> +	tzcntl	%eax, %eax
> +	addq	$(VEC_SIZE + 1), %rdi
> +	addq	%rdi, %rax
> +	VZEROUPPER_RETURN
>  
> -	addq	$VEC_SIZE, %rdi
> +	.p2align 4
> +L(first_vec_x3):
> +	tzcntl	%eax, %eax
> +	addq	$(VEC_SIZE * 2 + 1), %rdi
> +	addq	%rdi, %rax
> +	VZEROUPPER_RETURN
>  
> -# ifndef USE_AS_RAWMEMCHR
> -	subq	$(VEC_SIZE * 4), %rdx
> -	jbe	L(last_4x_vec_or_less)
> -# endif
>  
> -L(more_4x_vec):
> -	/* 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)
> +	.p2align 4
> +L(first_vec_x4):
> +	tzcntl	%eax, %eax
> +	addq	$(VEC_SIZE * 3 + 1), %rdi
> +	addq	%rdi, %rax
> +	VZEROUPPER_RETURN
>  
> -	VPCMPEQ VEC_SIZE(%rdi), %ymm0, %ymm1
> +	.p2align 4
> +L(aligned_more):
> +	/* Check the first 4 * VEC_SIZE.  Only one
> +	   VEC_SIZE at a time since data is only aligned to
> +	   VEC_SIZE.  */

Fit comments to 72 columns.

> +
> +# ifndef USE_AS_RAWMEMCHR
> +L(cross_page_continue):
> +	/* Align data to VEC_SIZE - 1.  */
> +	xorl	%ecx, %ecx
> +	subl	%edi, %ecx
> +	orq	$(VEC_SIZE - 1), %rdi
> +	/* esi is for adjusting length to see if near the
> +	   end.  */

Fit comments to 72 columns.

> +	leal	(VEC_SIZE * 4 + 1)(%rdi, %rcx), %esi
> +# else
> +	orq	$(VEC_SIZE - 1), %rdi
> +L(cross_page_continue):
> +# endif
> +	/* Load first VEC regardless.  */
> +	VPCMPEQ	1(%rdi), %ymm0, %ymm1
>  	vpmovmskb %ymm1, %eax
> +# ifndef USE_AS_RAWMEMCHR
> +	/* Adjust length. If near end handle specially.
> +	 */

Put the comments on one line.

> +	subq	%rsi, %rdx
> +	jbe	L(last_4x_vec_or_less)
> +# endif
>  	testl	%eax, %eax
>  	jnz	L(first_vec_x1)
>  
> -	VPCMPEQ (VEC_SIZE * 2)(%rdi), %ymm0, %ymm1
> +	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
> +	VPCMPEQ	(VEC_SIZE * 2 + 1)(%rdi), %ymm0, %ymm1
>  	vpmovmskb %ymm1, %eax
>  	testl	%eax, %eax
>  	jnz	L(first_vec_x3)
>  
> -	addq	$(VEC_SIZE * 4), %rdi
> +	VPCMPEQ	(VEC_SIZE * 3 + 1)(%rdi), %ymm0, %ymm1
> +	vpmovmskb %ymm1, %eax
> +	testl	%eax, %eax
> +	jnz	L(first_vec_x4)
>  
>  # ifndef USE_AS_RAWMEMCHR
> +	/* Check if at last VEC_SIZE * 4 length.  */
>  	subq	$(VEC_SIZE * 4), %rdx
> -	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
> -
> -# ifndef USE_AS_RAWMEMCHR
> -	/* Adjust length.  */
> +	jbe	L(last_4x_vec_or_less_cmpeq)
> +	/* Align data to VEC_SIZE * 4 - 1 for the  loop
> +	   and readjust length.  */
> +	incq	%rdi
> +	movl	%edi, %ecx
> +	orq	$(VEC_SIZE * 4 - 1), %rdi
> +	andl	$(VEC_SIZE * 4 - 1), %ecx
>  	addq	%rcx, %rdx
> +# else
> +	/* Align data to VEC_SIZE * 4 - 1 for loop.  */
> +	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.  */
> -	VPCMPEQ (%rdi), %ymm0, %ymm1
> -	VPCMPEQ VEC_SIZE(%rdi), %ymm0, %ymm2
> -	VPCMPEQ (VEC_SIZE * 2)(%rdi), %ymm0, %ymm3
> -	VPCMPEQ (VEC_SIZE * 3)(%rdi), %ymm0, %ymm4
> -
> +	VPCMPEQ	1(%rdi), %ymm0, %ymm1
> +	VPCMPEQ	(VEC_SIZE + 1)(%rdi), %ymm0, %ymm2
> +	VPCMPEQ	(VEC_SIZE * 2 + 1)(%rdi), %ymm0, %ymm3
> +	VPCMPEQ	(VEC_SIZE * 3 + 1)(%rdi), %ymm0, %ymm4
>  	vpor	%ymm1, %ymm2, %ymm5
>  	vpor	%ymm3, %ymm4, %ymm6
>  	vpor	%ymm5, %ymm6, %ymm5
>  
> -	vpmovmskb %ymm5, %eax
> -	testl	%eax, %eax
> -	jnz	L(4x_vec_end)
> -
> -	addq	$(VEC_SIZE * 4), %rdi
> -
> +	vpmovmskb %ymm5, %ecx
>  # ifdef USE_AS_RAWMEMCHR
> -	jmp	L(loop_4x_vec)
> +	subq	$-(VEC_SIZE * 4), %rdi
> +	testl	%ecx, %ecx
> +	jz	L(loop_4x_vec)
>  # else
> -	subq	$(VEC_SIZE * 4), %rdx
> -	ja	L(loop_4x_vec)
> +	testl	%ecx, %ecx
> +	jnz	L(loop_4x_vec_end)
>  
> -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)
> +	subq	$-(VEC_SIZE * 4), %rdi
>  
> -	VPCMPEQ (%rdi), %ymm0, %ymm1
> -	vpmovmskb %ymm1, %eax
> -	testl	%eax, %eax
> -	jnz	L(first_vec_x0)
> +	subq	$(VEC_SIZE * 4), %rdx
> +	ja	L(loop_4x_vec)
>  
> -	VPCMPEQ VEC_SIZE(%rdi), %ymm0, %ymm1
> +	/* Fall through into less than 4 remaining
> +	   vectors of length case.  */

Fit comments to 72 columns.

> +	VPCMPEQ	(VEC_SIZE * 0 + 1)(%rdi), %ymm0, %ymm1
>  	vpmovmskb %ymm1, %eax
> +	.p2align 4
> +L(last_4x_vec_or_less):
> +	/* Check if first VEC contained match.  */
>  	testl	%eax, %eax
> -	jnz	L(first_vec_x1)
> +	jnz	L(first_vec_x1_check)
>  
> -	VPCMPEQ (VEC_SIZE * 2)(%rdi), %ymm0, %ymm1
> -	vpmovmskb %ymm1, %eax
> -	testl	%eax, %eax
> +	/* If remaining length > VEC_SIZE * 2.  */
> +	addl	$(VEC_SIZE * 2), %edx
> +	jg	L(last_4x_vec)
>  
> -	jnz	L(first_vec_x2_check)
> -	subl	$VEC_SIZE, %edx
> -	jle	L(zero)
> +L(last_2x_vec):
> +	/* If remaining length < VEC_SIZE.  */
> +	addl	$VEC_SIZE, %edx
> +	jle	L(zero_end)
>  
> -	VPCMPEQ (VEC_SIZE * 3)(%rdi), %ymm0, %ymm1
> +	/* Check VEC2 and compare any match with
> +	   remaining length.  */

Fit comments to 72 columns.

> +	VPCMPEQ	(VEC_SIZE + 1)(%rdi), %ymm0, %ymm1
>  	vpmovmskb %ymm1, %eax
> -	testl	%eax, %eax
> -
> -	jnz	L(first_vec_x3_check)
> -	xorl	%eax, %eax
> +	tzcntl	%eax, %eax
> +	cmpl	%eax, %edx
> +	jbe	L(set_zero_end)
> +	addq	$(VEC_SIZE + 1), %rdi
> +	addq	%rdi, %rax
> +L(zero_end):
>  	VZEROUPPER_RETURN
>  
>  	.p2align 4
> -L(last_2x_vec):
> -	addl	$(VEC_SIZE * 2), %edx
> -	VPCMPEQ (%rdi), %ymm0, %ymm1
> +L(loop_4x_vec_end):
> +# endif
> +	/* rawmemchr will fall through into this if match
> +	   was found in loop.  */

Fit comments to 72 columns.

> +
>  	vpmovmskb %ymm1, %eax
>  	testl	%eax, %eax
> +	jnz	L(last_vec_x1_return)
>  
> -	jnz	L(first_vec_x0_check)
> -	subl	$VEC_SIZE, %edx
> -	jle	L(zero)
> -
> -	VPCMPEQ VEC_SIZE(%rdi), %ymm0, %ymm1
> -	vpmovmskb %ymm1, %eax
> +	vpmovmskb %ymm2, %eax
>  	testl	%eax, %eax
> -	jnz	L(first_vec_x1_check)
> -	xorl	%eax, %eax
> -	VZEROUPPER_RETURN
> +	jnz	L(last_vec_x2_return)
>  
> -	.p2align 4
> -L(first_vec_x0_check):
> -	tzcntl	%eax, %eax
> -	/* Check the end of data.  */
> -	cmpq	%rax, %rdx
> -	jbe	L(zero)
> +	vpmovmskb %ymm3, %eax
> +	/* Combine VEC3 matches (eax) with VEC4 matches
> +	   (ecx).  */

Fit comments to 72 columns.

> +	salq	$32, %rcx
> +	orq	%rcx, %rax
> +	tzcntq	%rax, %rax
> +# ifdef USE_AS_RAWMEMCHR
> +	subq	$(VEC_SIZE * 2 - 1), %rdi
> +# else
> +	subq	$-(VEC_SIZE * 2 + 1), %rdi
> +# endif
>  	addq	%rdi, %rax
>  	VZEROUPPER_RETURN
> +# ifndef USE_AS_RAWMEMCHR
>  
>  	.p2align 4
>  L(first_vec_x1_check):
>  	tzcntl	%eax, %eax
> -	/* Check the end of data.  */
> -	cmpq	%rax, %rdx
> -	jbe	L(zero)
> -	addq	$VEC_SIZE, %rax
> +	/* Adjust length.  */
> +	subl	$-(VEC_SIZE * 4), %edx
> +	/* Check if match within remaining length.  */
> +	cmpl	%eax, %edx
> +	jbe	L(set_zero_end)
> +	incq	%rdi
>  	addq	%rdi, %rax
>  	VZEROUPPER_RETURN
> +	.p2align 4
> +L(set_zero_end):
> +	xorl	%eax, %eax
> +	VZEROUPPER_RETURN
> +# endif
>  
>  	.p2align 4
> -L(first_vec_x2_check):
> +L(last_vec_x1_return):
>  	tzcntl	%eax, %eax
> -	/* Check the end of data.  */
> -	cmpq	%rax, %rdx
> -	jbe	L(zero)
> -	addq	$(VEC_SIZE * 2), %rax
> +# ifdef USE_AS_RAWMEMCHR
> +	subq	$(VEC_SIZE * 4 - 1), %rdi
> +# else
> +	incq	%rdi
> +# endif
>  	addq	%rdi, %rax
>  	VZEROUPPER_RETURN
>  
>  	.p2align 4
> -L(first_vec_x3_check):
> +L(last_vec_x2_return):
>  	tzcntl	%eax, %eax
> -	/* Check the end of data.  */
> -	cmpq	%rax, %rdx
> -	jbe	L(zero)
> -	addq	$(VEC_SIZE * 3), %rax
> +# ifdef USE_AS_RAWMEMCHR
> +	subq	$(VEC_SIZE * 3 - 1), %rdi
> +# else
> +	subq	$-(VEC_SIZE + 1), %rdi
> +# endif
>  	addq	%rdi, %rax
>  	VZEROUPPER_RETURN
>  
> +# ifndef USE_AS_RAWMEMCHR
>  	.p2align 4
> -L(zero):
> -	xorl	%eax, %eax
> -	jmp     L(return_vzeroupper)
> +L(last_4x_vec_or_less_cmpeq):
> +	VPCMPEQ	(VEC_SIZE * 4 + 1)(%rdi), %ymm0, %ymm1
> +	vpmovmskb %ymm1, %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	$(VEC_SIZE * 2), %edx
> +	jle	L(last_2x_vec)
>  	.p2align 4
> -L(null):
> -	xorl	%eax, %eax
> -	ret
> -# endif
> +L(last_4x_vec):
> +	VPCMPEQ	(VEC_SIZE + 1)(%rdi), %ymm0, %ymm1
> +	vpmovmskb %ymm1, %eax
> +	testl	%eax, %eax
> +	jnz	L(last_vec_x2_return)
>  
> -	.p2align 4
> -L(first_vec_x0):
> -	tzcntl	%eax, %eax
> -	addq	%rdi, %rax
> -	VZEROUPPER_RETURN
> +	VPCMPEQ	(VEC_SIZE * 2 + 1)(%rdi), %ymm0, %ymm1
> +	vpmovmskb %ymm1, %eax
>  
> -	.p2align 4
> -L(first_vec_x1):
> -	tzcntl	%eax, %eax
> -	addq	$VEC_SIZE, %rax
> -	addq	%rdi, %rax
> -	VZEROUPPER_RETURN
> +	/* Create mask for possible matches within
> +	   remaining length.  */

Fit comments to 72 columns.

> +	movq	$-1, %rcx
> +	bzhiq	%rdx, %rcx, %rcx
>  
> -	.p2align 4
> -L(first_vec_x2):
> +	/* Test matches in data against length match.  */
> +	andl	%ecx, %eax
> +	jnz	L(last_vec_x3)
> +
> +	/* if remaining length <= VEC_SIZE * 3 (Note this
> +	   is after remaining length was found to be > VEC_SIZE * 2.

Fit comments to 72 columns.

> +	 */
> +	subl	$VEC_SIZE, %edx
> +	jbe	L(zero_end2)
> +
> +	VPCMPEQ	(VEC_SIZE * 3 + 1)(%rdi), %ymm0, %ymm1
> +	vpmovmskb %ymm1, %eax
> +	/* Shift remaining length mask for last VEC.  */
> +	shrq	$32, %rcx
> +	andl	%ecx, %eax
> +	jz	L(zero_end2)
>  	tzcntl	%eax, %eax
> -	addq	$(VEC_SIZE * 2), %rax
> +	addq	$(VEC_SIZE * 3 + 1), %rdi
>  	addq	%rdi, %rax
> +L(zero_end2):
>  	VZEROUPPER_RETURN
>  
>  	.p2align 4
> -L(4x_vec_end):
> -	vpmovmskb %ymm1, %eax
> -	testl	%eax, %eax
> -	jnz	L(first_vec_x0)
> -	vpmovmskb %ymm2, %eax
> -	testl	%eax, %eax
> -	jnz	L(first_vec_x1)
> -	vpmovmskb %ymm3, %eax
> -	testl	%eax, %eax
> -	jnz	L(first_vec_x2)
> -	vpmovmskb %ymm4, %eax
> -	testl	%eax, %eax
> -L(first_vec_x3):
> +L(last_vec_x3):
>  	tzcntl	%eax, %eax
> -	addq	$(VEC_SIZE * 3), %rax
> +	subq	$-(VEC_SIZE * 2 + 1), %rdi
>  	addq	%rdi, %rax
>  	VZEROUPPER_RETURN
> +# endif
>  
> -END (MEMCHR)
> +END(MEMCHR)

No need for this change.

>  #endif
> -- 
> 2.29.2
> 

Thanks.

H.J.
Noah Goldstein May 3, 2021, 8:06 p.m. UTC | #2
On Mon, May 3, 2021 at 2:50 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Mon, May 03, 2021 at 04:44:36AM -0400, Noah Goldstein wrote:
> > No bug. This commit optimizes memchr-avx2.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,
> > asaving a few instructions the in loop return 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-avx2.S | 446 +++++++++++++++----------
> >  1 file changed, 262 insertions(+), 184 deletions(-)
> >
> > diff --git a/sysdeps/x86_64/multiarch/memchr-avx2.S b/sysdeps/x86_64/multiarch/memchr-avx2.S
> > index 1fcb1c350f..8368fcd1e1 100644
> > --- a/sysdeps/x86_64/multiarch/memchr-avx2.S
> > +++ b/sysdeps/x86_64/multiarch/memchr-avx2.S
> > @@ -26,8 +26,22 @@
> >
> >  # ifdef USE_AS_WMEMCHR
> >  #  define VPCMPEQ    vpcmpeqd
> > +#  define VPBROADCAST        vpbroadcastd
> > +#  define CHAR_SIZE  4
> >  # else
> >  #  define VPCMPEQ    vpcmpeqb
> > +#  define VPBROADCAST        vpbroadcastb
> > +#  define CHAR_SIZE  1
> > +# endif
> > +
> > +# ifdef USE_AS_RAWMEMCHR
> > +#  define ERAW_PTR_REG       ecx
> > +#  define RRAW_PTR_REG       rcx
> > +#  define ALGN_PTR_REG       rdi
> > +# else
> > +#  define ERAW_PTR_REG       edi
> > +#  define RRAW_PTR_REG       rdi
> > +#  define ALGN_PTR_REG       rcx
> >  # endif
> >
> >  # ifndef VZEROUPPER
> > @@ -39,303 +53,367 @@
> >  # endif
> >
> >  # define VEC_SIZE 32
> > +# define PAGE_SIZE 4096
> > +
>
> Remove the extra line here.

Done.

>
> >
> >       .section SECTION(.text),"ax",@progbits
> > -ENTRY (MEMCHR)
> > +ENTRY(MEMCHR)
>
> No need for this change.

Fixed.

>
> >  # ifndef USE_AS_RAWMEMCHR
> >       /* Check for zero length.  */
> >       test    %RDX_LP, %RDX_LP
> >       jz      L(null)
> >  # endif
> > -     movl    %edi, %ecx
> > -     /* Broadcast CHAR to YMM0.  */
> > -     vmovd   %esi, %xmm0
> >  # ifdef USE_AS_WMEMCHR
> >       shl     $2, %RDX_LP
> > -     vpbroadcastd %xmm0, %ymm0
> >  # else
> >  #  ifdef __ILP32__
> >       /* Clear the upper 32 bits.  */
> >       movl    %edx, %edx
> >  #  endif
> > -     vpbroadcastb %xmm0, %ymm0
> >  # endif
> > -     /* 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)
> > +     /* Broadcast CHAR to YMMMATCH.  */
> > +     vmovd   %esi, %xmm0
> > +     VPBROADCAST %xmm0, %ymm0
> > +     /* Check if we may cross page boundary with one
> > +        vector load.  */
> > +     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.  */
> > -     VPCMPEQ (%rdi), %ymm0, %ymm1
> > +     VPCMPEQ (%rdi), %ymm0, %ymm1
> >       vpmovmskb %ymm1, %eax
> > -     testl   %eax, %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)
> > -# else
> > -     jnz     L(first_vec_x0)
> > +     /* If length < CHAR_PER_VEC handle special.  */
> > +     cmpq    $VEC_SIZE, %rdx
> > +     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
> > +     addq    %rdi, %rax
> > +     VZEROUPPER_RETURN
> >
> >  # ifndef USE_AS_RAWMEMCHR
> > -     /* Adjust length.  */
> > -     addq    %rcx, %rdx
> > -
> > -     subq    $(VEC_SIZE * 4), %rdx
> > -     jbe     L(last_4x_vec_or_less)
> > +     .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), %rax
> > +     cmovle  %rcx, %rax
> > +     VZEROUPPER_RETURN
> > +L(null):
> > +     xorl    %eax, %eax
> > +     ret
> >  # 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
> > +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
>
> Fit comments to 72 columns.

Fixed. Still working out the kinks in my formatter.
For the 72 column fill does tab count as 1, 4, or 8 units?

>
> > +        memchr.  */
> > +     movq    %rdi, %rcx
> > +     /* Align data to VEC_SIZE - 1. ALGN_PTR_REG is
> > +        rcx for memchr and rdi for rawmemchr.  */
> > +     orq     $(VEC_SIZE - 1), %ALGN_PTR_REG
> > +     VPCMPEQ -(VEC_SIZE - 1)(%ALGN_PTR_REG), %ymm0, %ymm1
> >       vpmovmskb %ymm1, %eax
> > +# ifndef USE_AS_RAWMEMCHR
> > +     /* Calculate length until end of page (length
> > +        checked for a match).  */
> > +     leaq    1(%ALGN_PTR_REG), %rsi
> > +     subq    %RRAW_PTR_REG, %rsi
> > +# endif
> >       /* Remove the leading bytes.  */
> > -     sarl    %cl, %eax
> > -     testl   %eax, %eax
> > -     jz      L(aligned_more)
> > -     tzcntl  %eax, %eax
> > +     sarxl   %ERAW_PTR_REG, %eax, %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
> > -     addq    %rdi, %rax
> > -     addq    %rcx, %rax
> > +     testl   %eax, %eax
> > +     jz      L(cross_page_continue)
> > +     tzcntl  %eax, %eax
> > +     addq    %RRAW_PTR_REG, %rax
> >  L(return_vzeroupper):
> >       ZERO_UPPER_VEC_REGISTERS_RETURN
> >
> >       .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
> > +     incq    %rdi
> > +     addq    %rdi, %rax
> > +     VZEROUPPER_RETURN
> >
> > -     /* Check the end of data.  */
> > -     subq    %rcx, %rdx
> > -     jbe     L(zero)
> > -# endif
> > +     .p2align 4
> > +L(first_vec_x2):
> > +     tzcntl  %eax, %eax
> > +     addq    $(VEC_SIZE + 1), %rdi
> > +     addq    %rdi, %rax
> > +     VZEROUPPER_RETURN
> >
> > -     addq    $VEC_SIZE, %rdi
> > +     .p2align 4
> > +L(first_vec_x3):
> > +     tzcntl  %eax, %eax
> > +     addq    $(VEC_SIZE * 2 + 1), %rdi
> > +     addq    %rdi, %rax
> > +     VZEROUPPER_RETURN
> >
> > -# ifndef USE_AS_RAWMEMCHR
> > -     subq    $(VEC_SIZE * 4), %rdx
> > -     jbe     L(last_4x_vec_or_less)
> > -# endif
> >
> > -L(more_4x_vec):
> > -     /* 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)
> > +     .p2align 4
> > +L(first_vec_x4):
> > +     tzcntl  %eax, %eax
> > +     addq    $(VEC_SIZE * 3 + 1), %rdi
> > +     addq    %rdi, %rax
> > +     VZEROUPPER_RETURN
> >
> > -     VPCMPEQ VEC_SIZE(%rdi), %ymm0, %ymm1
> > +     .p2align 4
> > +L(aligned_more):
> > +     /* Check the first 4 * VEC_SIZE.  Only one
> > +        VEC_SIZE at a time since data is only aligned to
> > +        VEC_SIZE.  */
>
> Fit comments to 72 columns.

Adjusted closer. Hopefully fixed.

>
> > +
> > +# ifndef USE_AS_RAWMEMCHR
> > +L(cross_page_continue):
> > +     /* Align data to VEC_SIZE - 1.  */
> > +     xorl    %ecx, %ecx
> > +     subl    %edi, %ecx
> > +     orq     $(VEC_SIZE - 1), %rdi
> > +     /* esi is for adjusting length to see if near the
> > +        end.  */
>
> Fit comments to 72 columns.

Adjusted closer. Hopefully fixed.

>
> > +     leal    (VEC_SIZE * 4 + 1)(%rdi, %rcx), %esi
> > +# else
> > +     orq     $(VEC_SIZE - 1), %rdi
> > +L(cross_page_continue):
> > +# endif
> > +     /* Load first VEC regardless.  */
> > +     VPCMPEQ 1(%rdi), %ymm0, %ymm1
> >       vpmovmskb %ymm1, %eax
> > +# ifndef USE_AS_RAWMEMCHR
> > +     /* Adjust length. If near end handle specially.
> > +      */
>
> Put the comments on one line.

Fixed.

>
> > +     subq    %rsi, %rdx
> > +     jbe     L(last_4x_vec_or_less)
> > +# endif
> >       testl   %eax, %eax
> >       jnz     L(first_vec_x1)
> >
> > -     VPCMPEQ (VEC_SIZE * 2)(%rdi), %ymm0, %ymm1
> > +     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
> > +     VPCMPEQ (VEC_SIZE * 2 + 1)(%rdi), %ymm0, %ymm1
> >       vpmovmskb %ymm1, %eax
> >       testl   %eax, %eax
> >       jnz     L(first_vec_x3)
> >
> > -     addq    $(VEC_SIZE * 4), %rdi
> > +     VPCMPEQ (VEC_SIZE * 3 + 1)(%rdi), %ymm0, %ymm1
> > +     vpmovmskb %ymm1, %eax
> > +     testl   %eax, %eax
> > +     jnz     L(first_vec_x4)
> >
> >  # ifndef USE_AS_RAWMEMCHR
> > +     /* Check if at last VEC_SIZE * 4 length.  */
> >       subq    $(VEC_SIZE * 4), %rdx
> > -     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
> > -
> > -# ifndef USE_AS_RAWMEMCHR
> > -     /* Adjust length.  */
> > +     jbe     L(last_4x_vec_or_less_cmpeq)
> > +     /* Align data to VEC_SIZE * 4 - 1 for the  loop
> > +        and readjust length.  */
> > +     incq    %rdi
> > +     movl    %edi, %ecx
> > +     orq     $(VEC_SIZE * 4 - 1), %rdi
> > +     andl    $(VEC_SIZE * 4 - 1), %ecx
> >       addq    %rcx, %rdx
> > +# else
> > +     /* Align data to VEC_SIZE * 4 - 1 for loop.  */
> > +     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.  */
> > -     VPCMPEQ (%rdi), %ymm0, %ymm1
> > -     VPCMPEQ VEC_SIZE(%rdi), %ymm0, %ymm2
> > -     VPCMPEQ (VEC_SIZE * 2)(%rdi), %ymm0, %ymm3
> > -     VPCMPEQ (VEC_SIZE * 3)(%rdi), %ymm0, %ymm4
> > -
> > +     VPCMPEQ 1(%rdi), %ymm0, %ymm1
> > +     VPCMPEQ (VEC_SIZE + 1)(%rdi), %ymm0, %ymm2
> > +     VPCMPEQ (VEC_SIZE * 2 + 1)(%rdi), %ymm0, %ymm3
> > +     VPCMPEQ (VEC_SIZE * 3 + 1)(%rdi), %ymm0, %ymm4
> >       vpor    %ymm1, %ymm2, %ymm5
> >       vpor    %ymm3, %ymm4, %ymm6
> >       vpor    %ymm5, %ymm6, %ymm5
> >
> > -     vpmovmskb %ymm5, %eax
> > -     testl   %eax, %eax
> > -     jnz     L(4x_vec_end)
> > -
> > -     addq    $(VEC_SIZE * 4), %rdi
> > -
> > +     vpmovmskb %ymm5, %ecx
> >  # ifdef USE_AS_RAWMEMCHR
> > -     jmp     L(loop_4x_vec)
> > +     subq    $-(VEC_SIZE * 4), %rdi
> > +     testl   %ecx, %ecx
> > +     jz      L(loop_4x_vec)
> >  # else
> > -     subq    $(VEC_SIZE * 4), %rdx
> > -     ja      L(loop_4x_vec)
> > +     testl   %ecx, %ecx
> > +     jnz     L(loop_4x_vec_end)
> >
> > -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)
> > +     subq    $-(VEC_SIZE * 4), %rdi
> >
> > -     VPCMPEQ (%rdi), %ymm0, %ymm1
> > -     vpmovmskb %ymm1, %eax
> > -     testl   %eax, %eax
> > -     jnz     L(first_vec_x0)
> > +     subq    $(VEC_SIZE * 4), %rdx
> > +     ja      L(loop_4x_vec)
> >
> > -     VPCMPEQ VEC_SIZE(%rdi), %ymm0, %ymm1
> > +     /* Fall through into less than 4 remaining
> > +        vectors of length case.  */
>
> Fit comments to 72 columns.

Adjusted closer. Hopefully fixed.

>
> > +     VPCMPEQ (VEC_SIZE * 0 + 1)(%rdi), %ymm0, %ymm1
> >       vpmovmskb %ymm1, %eax
> > +     .p2align 4
> > +L(last_4x_vec_or_less):
> > +     /* Check if first VEC contained match.  */
> >       testl   %eax, %eax
> > -     jnz     L(first_vec_x1)
> > +     jnz     L(first_vec_x1_check)
> >
> > -     VPCMPEQ (VEC_SIZE * 2)(%rdi), %ymm0, %ymm1
> > -     vpmovmskb %ymm1, %eax
> > -     testl   %eax, %eax
> > +     /* If remaining length > VEC_SIZE * 2.  */
> > +     addl    $(VEC_SIZE * 2), %edx
> > +     jg      L(last_4x_vec)
> >
> > -     jnz     L(first_vec_x2_check)
> > -     subl    $VEC_SIZE, %edx
> > -     jle     L(zero)
> > +L(last_2x_vec):
> > +     /* If remaining length < VEC_SIZE.  */
> > +     addl    $VEC_SIZE, %edx
> > +     jle     L(zero_end)
> >
> > -     VPCMPEQ (VEC_SIZE * 3)(%rdi), %ymm0, %ymm1
> > +     /* Check VEC2 and compare any match with
> > +        remaining length.  */
>
> Fit comments to 72 columns.

Adjusted closer. Hopefully fixed.
>
> > +     VPCMPEQ (VEC_SIZE + 1)(%rdi), %ymm0, %ymm1
> >       vpmovmskb %ymm1, %eax
> > -     testl   %eax, %eax
> > -
> > -     jnz     L(first_vec_x3_check)
> > -     xorl    %eax, %eax
> > +     tzcntl  %eax, %eax
> > +     cmpl    %eax, %edx
> > +     jbe     L(set_zero_end)
> > +     addq    $(VEC_SIZE + 1), %rdi
> > +     addq    %rdi, %rax
> > +L(zero_end):
> >       VZEROUPPER_RETURN
> >
> >       .p2align 4
> > -L(last_2x_vec):
> > -     addl    $(VEC_SIZE * 2), %edx
> > -     VPCMPEQ (%rdi), %ymm0, %ymm1
> > +L(loop_4x_vec_end):
> > +# endif
> > +     /* rawmemchr will fall through into this if match
> > +        was found in loop.  */
>
> Fit comments to 72 columns.

Adjusted closer. Hopefully fixed.

>
> > +
> >       vpmovmskb %ymm1, %eax
> >       testl   %eax, %eax
> > +     jnz     L(last_vec_x1_return)
> >
> > -     jnz     L(first_vec_x0_check)
> > -     subl    $VEC_SIZE, %edx
> > -     jle     L(zero)
> > -
> > -     VPCMPEQ VEC_SIZE(%rdi), %ymm0, %ymm1
> > -     vpmovmskb %ymm1, %eax
> > +     vpmovmskb %ymm2, %eax
> >       testl   %eax, %eax
> > -     jnz     L(first_vec_x1_check)
> > -     xorl    %eax, %eax
> > -     VZEROUPPER_RETURN
> > +     jnz     L(last_vec_x2_return)
> >
> > -     .p2align 4
> > -L(first_vec_x0_check):
> > -     tzcntl  %eax, %eax
> > -     /* Check the end of data.  */
> > -     cmpq    %rax, %rdx
> > -     jbe     L(zero)
> > +     vpmovmskb %ymm3, %eax
> > +     /* Combine VEC3 matches (eax) with VEC4 matches
> > +        (ecx).  */
>
> Fit comments to 72 columns.

Adjusted closer. Hopefully fixed.

>
> > +     salq    $32, %rcx
> > +     orq     %rcx, %rax
> > +     tzcntq  %rax, %rax
> > +# ifdef USE_AS_RAWMEMCHR
> > +     subq    $(VEC_SIZE * 2 - 1), %rdi
> > +# else
> > +     subq    $-(VEC_SIZE * 2 + 1), %rdi
> > +# endif
> >       addq    %rdi, %rax
> >       VZEROUPPER_RETURN
> > +# ifndef USE_AS_RAWMEMCHR
> >
> >       .p2align 4
> >  L(first_vec_x1_check):
> >       tzcntl  %eax, %eax
> > -     /* Check the end of data.  */
> > -     cmpq    %rax, %rdx
> > -     jbe     L(zero)
> > -     addq    $VEC_SIZE, %rax
> > +     /* Adjust length.  */
> > +     subl    $-(VEC_SIZE * 4), %edx
> > +     /* Check if match within remaining length.  */
> > +     cmpl    %eax, %edx
> > +     jbe     L(set_zero_end)
> > +     incq    %rdi
> >       addq    %rdi, %rax
> >       VZEROUPPER_RETURN
> > +     .p2align 4
> > +L(set_zero_end):
> > +     xorl    %eax, %eax
> > +     VZEROUPPER_RETURN
> > +# endif
> >
> >       .p2align 4
> > -L(first_vec_x2_check):
> > +L(last_vec_x1_return):
> >       tzcntl  %eax, %eax
> > -     /* Check the end of data.  */
> > -     cmpq    %rax, %rdx
> > -     jbe     L(zero)
> > -     addq    $(VEC_SIZE * 2), %rax
> > +# ifdef USE_AS_RAWMEMCHR
> > +     subq    $(VEC_SIZE * 4 - 1), %rdi
> > +# else
> > +     incq    %rdi
> > +# endif
> >       addq    %rdi, %rax
> >       VZEROUPPER_RETURN
> >
> >       .p2align 4
> > -L(first_vec_x3_check):
> > +L(last_vec_x2_return):
> >       tzcntl  %eax, %eax
> > -     /* Check the end of data.  */
> > -     cmpq    %rax, %rdx
> > -     jbe     L(zero)
> > -     addq    $(VEC_SIZE * 3), %rax
> > +# ifdef USE_AS_RAWMEMCHR
> > +     subq    $(VEC_SIZE * 3 - 1), %rdi
> > +# else
> > +     subq    $-(VEC_SIZE + 1), %rdi
> > +# endif
> >       addq    %rdi, %rax
> >       VZEROUPPER_RETURN
> >
> > +# ifndef USE_AS_RAWMEMCHR
> >       .p2align 4
> > -L(zero):
> > -     xorl    %eax, %eax
> > -     jmp     L(return_vzeroupper)
> > +L(last_4x_vec_or_less_cmpeq):
> > +     VPCMPEQ (VEC_SIZE * 4 + 1)(%rdi), %ymm0, %ymm1
> > +     vpmovmskb %ymm1, %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    $(VEC_SIZE * 2), %edx
> > +     jle     L(last_2x_vec)
> >       .p2align 4
> > -L(null):
> > -     xorl    %eax, %eax
> > -     ret
> > -# endif
> > +L(last_4x_vec):
> > +     VPCMPEQ (VEC_SIZE + 1)(%rdi), %ymm0, %ymm1
> > +     vpmovmskb %ymm1, %eax
> > +     testl   %eax, %eax
> > +     jnz     L(last_vec_x2_return)
> >
> > -     .p2align 4
> > -L(first_vec_x0):
> > -     tzcntl  %eax, %eax
> > -     addq    %rdi, %rax
> > -     VZEROUPPER_RETURN
> > +     VPCMPEQ (VEC_SIZE * 2 + 1)(%rdi), %ymm0, %ymm1
> > +     vpmovmskb %ymm1, %eax
> >
> > -     .p2align 4
> > -L(first_vec_x1):
> > -     tzcntl  %eax, %eax
> > -     addq    $VEC_SIZE, %rax
> > -     addq    %rdi, %rax
> > -     VZEROUPPER_RETURN
> > +     /* Create mask for possible matches within
> > +        remaining length.  */
>
> Fit comments to 72 columns.

Adjusted closer. Hopefully fixed.

>
> > +     movq    $-1, %rcx
> > +     bzhiq   %rdx, %rcx, %rcx
> >
> > -     .p2align 4
> > -L(first_vec_x2):
> > +     /* Test matches in data against length match.  */
> > +     andl    %ecx, %eax
> > +     jnz     L(last_vec_x3)
> > +
> > +     /* if remaining length <= VEC_SIZE * 3 (Note this
> > +        is after remaining length was found to be > VEC_SIZE * 2.
>
> Fit comments to 72 columns.

Adjusted closer. Hopefully fixed.

>
> > +      */
> > +     subl    $VEC_SIZE, %edx
> > +     jbe     L(zero_end2)
> > +
> > +     VPCMPEQ (VEC_SIZE * 3 + 1)(%rdi), %ymm0, %ymm1
> > +     vpmovmskb %ymm1, %eax
> > +     /* Shift remaining length mask for last VEC.  */
> > +     shrq    $32, %rcx
> > +     andl    %ecx, %eax
> > +     jz      L(zero_end2)
> >       tzcntl  %eax, %eax
> > -     addq    $(VEC_SIZE * 2), %rax
> > +     addq    $(VEC_SIZE * 3 + 1), %rdi
> >       addq    %rdi, %rax
> > +L(zero_end2):
> >       VZEROUPPER_RETURN
> >
> >       .p2align 4
> > -L(4x_vec_end):
> > -     vpmovmskb %ymm1, %eax
> > -     testl   %eax, %eax
> > -     jnz     L(first_vec_x0)
> > -     vpmovmskb %ymm2, %eax
> > -     testl   %eax, %eax
> > -     jnz     L(first_vec_x1)
> > -     vpmovmskb %ymm3, %eax
> > -     testl   %eax, %eax
> > -     jnz     L(first_vec_x2)
> > -     vpmovmskb %ymm4, %eax
> > -     testl   %eax, %eax
> > -L(first_vec_x3):
> > +L(last_vec_x3):
> >       tzcntl  %eax, %eax
> > -     addq    $(VEC_SIZE * 3), %rax
> > +     subq    $-(VEC_SIZE * 2 + 1), %rdi
> >       addq    %rdi, %rax
> >       VZEROUPPER_RETURN
> > +# endif
> >
> > -END (MEMCHR)
> > +END(MEMCHR)
>
> No need for this change.

Fixed.

>
> >  #endif
> > --
> > 2.29.2
> >
>
> Thanks.
>
> H.J.
diff mbox series

Patch

diff --git a/sysdeps/x86_64/multiarch/memchr-avx2.S b/sysdeps/x86_64/multiarch/memchr-avx2.S
index 1fcb1c350f..8368fcd1e1 100644
--- a/sysdeps/x86_64/multiarch/memchr-avx2.S
+++ b/sysdeps/x86_64/multiarch/memchr-avx2.S
@@ -26,8 +26,22 @@ 
 
 # ifdef USE_AS_WMEMCHR
 #  define VPCMPEQ	vpcmpeqd
+#  define VPBROADCAST	vpbroadcastd
+#  define CHAR_SIZE	4
 # else
 #  define VPCMPEQ	vpcmpeqb
+#  define VPBROADCAST	vpbroadcastb
+#  define CHAR_SIZE	1
+# endif
+
+# ifdef USE_AS_RAWMEMCHR
+#  define ERAW_PTR_REG	ecx
+#  define RRAW_PTR_REG	rcx
+#  define ALGN_PTR_REG	rdi
+# else
+#  define ERAW_PTR_REG	edi
+#  define RRAW_PTR_REG	rdi
+#  define ALGN_PTR_REG	rcx
 # endif
 
 # ifndef VZEROUPPER
@@ -39,303 +53,367 @@ 
 # endif
 
 # define VEC_SIZE 32
+# define PAGE_SIZE 4096
+
 
 	.section SECTION(.text),"ax",@progbits
-ENTRY (MEMCHR)
+ENTRY(MEMCHR)
 # ifndef USE_AS_RAWMEMCHR
 	/* Check for zero length.  */
 	test	%RDX_LP, %RDX_LP
 	jz	L(null)
 # endif
-	movl	%edi, %ecx
-	/* Broadcast CHAR to YMM0.  */
-	vmovd	%esi, %xmm0
 # ifdef USE_AS_WMEMCHR
 	shl	$2, %RDX_LP
-	vpbroadcastd %xmm0, %ymm0
 # else
 #  ifdef __ILP32__
 	/* Clear the upper 32 bits.  */
 	movl	%edx, %edx
 #  endif
-	vpbroadcastb %xmm0, %ymm0
 # endif
-	/* 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)
+	/* Broadcast CHAR to YMMMATCH.  */
+	vmovd	%esi, %xmm0
+	VPBROADCAST %xmm0, %ymm0
+	/* Check if we may cross page boundary with one
+	   vector load.  */
+	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.  */
-	VPCMPEQ (%rdi), %ymm0, %ymm1
+	VPCMPEQ	(%rdi), %ymm0, %ymm1
 	vpmovmskb %ymm1, %eax
-	testl	%eax, %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)
-# else
-	jnz	L(first_vec_x0)
+	/* If length < CHAR_PER_VEC handle special.  */
+	cmpq	$VEC_SIZE, %rdx
+	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
+	addq	%rdi, %rax
+	VZEROUPPER_RETURN
 
 # ifndef USE_AS_RAWMEMCHR
-	/* Adjust length.  */
-	addq	%rcx, %rdx
-
-	subq	$(VEC_SIZE * 4), %rdx
-	jbe	L(last_4x_vec_or_less)
+	.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), %rax
+	cmovle	%rcx, %rax
+	VZEROUPPER_RETURN
+L(null):
+	xorl	%eax, %eax
+	ret
 # 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
+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 - 1. ALGN_PTR_REG is
+	   rcx for memchr and rdi for rawmemchr.  */
+	orq	$(VEC_SIZE - 1), %ALGN_PTR_REG
+	VPCMPEQ	-(VEC_SIZE - 1)(%ALGN_PTR_REG), %ymm0, %ymm1
 	vpmovmskb %ymm1, %eax
+# ifndef USE_AS_RAWMEMCHR
+	/* Calculate length until end of page (length
+	   checked for a match).  */
+	leaq	1(%ALGN_PTR_REG), %rsi
+	subq	%RRAW_PTR_REG, %rsi
+# endif
 	/* Remove the leading bytes.  */
-	sarl	%cl, %eax
-	testl	%eax, %eax
-	jz	L(aligned_more)
-	tzcntl	%eax, %eax
+	sarxl	%ERAW_PTR_REG, %eax, %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
-	addq	%rdi, %rax
-	addq	%rcx, %rax
+	testl	%eax, %eax
+	jz	L(cross_page_continue)
+	tzcntl	%eax, %eax
+	addq	%RRAW_PTR_REG, %rax
 L(return_vzeroupper):
 	ZERO_UPPER_VEC_REGISTERS_RETURN
 
 	.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
+	incq	%rdi
+	addq	%rdi, %rax
+	VZEROUPPER_RETURN
 
-	/* Check the end of data.  */
-	subq	%rcx, %rdx
-	jbe	L(zero)
-# endif
+	.p2align 4
+L(first_vec_x2):
+	tzcntl	%eax, %eax
+	addq	$(VEC_SIZE + 1), %rdi
+	addq	%rdi, %rax
+	VZEROUPPER_RETURN
 
-	addq	$VEC_SIZE, %rdi
+	.p2align 4
+L(first_vec_x3):
+	tzcntl	%eax, %eax
+	addq	$(VEC_SIZE * 2 + 1), %rdi
+	addq	%rdi, %rax
+	VZEROUPPER_RETURN
 
-# ifndef USE_AS_RAWMEMCHR
-	subq	$(VEC_SIZE * 4), %rdx
-	jbe	L(last_4x_vec_or_less)
-# endif
 
-L(more_4x_vec):
-	/* 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)
+	.p2align 4
+L(first_vec_x4):
+	tzcntl	%eax, %eax
+	addq	$(VEC_SIZE * 3 + 1), %rdi
+	addq	%rdi, %rax
+	VZEROUPPER_RETURN
 
-	VPCMPEQ VEC_SIZE(%rdi), %ymm0, %ymm1
+	.p2align 4
+L(aligned_more):
+	/* Check the first 4 * VEC_SIZE.  Only one
+	   VEC_SIZE at a time since data is only aligned to
+	   VEC_SIZE.  */
+
+# ifndef USE_AS_RAWMEMCHR
+L(cross_page_continue):
+	/* Align data to VEC_SIZE - 1.  */
+	xorl	%ecx, %ecx
+	subl	%edi, %ecx
+	orq	$(VEC_SIZE - 1), %rdi
+	/* esi is for adjusting length to see if near the
+	   end.  */
+	leal	(VEC_SIZE * 4 + 1)(%rdi, %rcx), %esi
+# else
+	orq	$(VEC_SIZE - 1), %rdi
+L(cross_page_continue):
+# endif
+	/* Load first VEC regardless.  */
+	VPCMPEQ	1(%rdi), %ymm0, %ymm1
 	vpmovmskb %ymm1, %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)
 
-	VPCMPEQ (VEC_SIZE * 2)(%rdi), %ymm0, %ymm1
+	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
+	VPCMPEQ	(VEC_SIZE * 2 + 1)(%rdi), %ymm0, %ymm1
 	vpmovmskb %ymm1, %eax
 	testl	%eax, %eax
 	jnz	L(first_vec_x3)
 
-	addq	$(VEC_SIZE * 4), %rdi
+	VPCMPEQ	(VEC_SIZE * 3 + 1)(%rdi), %ymm0, %ymm1
+	vpmovmskb %ymm1, %eax
+	testl	%eax, %eax
+	jnz	L(first_vec_x4)
 
 # ifndef USE_AS_RAWMEMCHR
+	/* Check if at last VEC_SIZE * 4 length.  */
 	subq	$(VEC_SIZE * 4), %rdx
-	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
-
-# ifndef USE_AS_RAWMEMCHR
-	/* Adjust length.  */
+	jbe	L(last_4x_vec_or_less_cmpeq)
+	/* Align data to VEC_SIZE * 4 - 1 for the  loop
+	   and readjust length.  */
+	incq	%rdi
+	movl	%edi, %ecx
+	orq	$(VEC_SIZE * 4 - 1), %rdi
+	andl	$(VEC_SIZE * 4 - 1), %ecx
 	addq	%rcx, %rdx
+# else
+	/* Align data to VEC_SIZE * 4 - 1 for loop.  */
+	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.  */
-	VPCMPEQ (%rdi), %ymm0, %ymm1
-	VPCMPEQ VEC_SIZE(%rdi), %ymm0, %ymm2
-	VPCMPEQ (VEC_SIZE * 2)(%rdi), %ymm0, %ymm3
-	VPCMPEQ (VEC_SIZE * 3)(%rdi), %ymm0, %ymm4
-
+	VPCMPEQ	1(%rdi), %ymm0, %ymm1
+	VPCMPEQ	(VEC_SIZE + 1)(%rdi), %ymm0, %ymm2
+	VPCMPEQ	(VEC_SIZE * 2 + 1)(%rdi), %ymm0, %ymm3
+	VPCMPEQ	(VEC_SIZE * 3 + 1)(%rdi), %ymm0, %ymm4
 	vpor	%ymm1, %ymm2, %ymm5
 	vpor	%ymm3, %ymm4, %ymm6
 	vpor	%ymm5, %ymm6, %ymm5
 
-	vpmovmskb %ymm5, %eax
-	testl	%eax, %eax
-	jnz	L(4x_vec_end)
-
-	addq	$(VEC_SIZE * 4), %rdi
-
+	vpmovmskb %ymm5, %ecx
 # ifdef USE_AS_RAWMEMCHR
-	jmp	L(loop_4x_vec)
+	subq	$-(VEC_SIZE * 4), %rdi
+	testl	%ecx, %ecx
+	jz	L(loop_4x_vec)
 # else
-	subq	$(VEC_SIZE * 4), %rdx
-	ja	L(loop_4x_vec)
+	testl	%ecx, %ecx
+	jnz	L(loop_4x_vec_end)
 
-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)
+	subq	$-(VEC_SIZE * 4), %rdi
 
-	VPCMPEQ (%rdi), %ymm0, %ymm1
-	vpmovmskb %ymm1, %eax
-	testl	%eax, %eax
-	jnz	L(first_vec_x0)
+	subq	$(VEC_SIZE * 4), %rdx
+	ja	L(loop_4x_vec)
 
-	VPCMPEQ VEC_SIZE(%rdi), %ymm0, %ymm1
+	/* Fall through into less than 4 remaining
+	   vectors of length case.  */
+	VPCMPEQ	(VEC_SIZE * 0 + 1)(%rdi), %ymm0, %ymm1
 	vpmovmskb %ymm1, %eax
+	.p2align 4
+L(last_4x_vec_or_less):
+	/* Check if first VEC contained match.  */
 	testl	%eax, %eax
-	jnz	L(first_vec_x1)
+	jnz	L(first_vec_x1_check)
 
-	VPCMPEQ (VEC_SIZE * 2)(%rdi), %ymm0, %ymm1
-	vpmovmskb %ymm1, %eax
-	testl	%eax, %eax
+	/* If remaining length > VEC_SIZE * 2.  */
+	addl	$(VEC_SIZE * 2), %edx
+	jg	L(last_4x_vec)
 
-	jnz	L(first_vec_x2_check)
-	subl	$VEC_SIZE, %edx
-	jle	L(zero)
+L(last_2x_vec):
+	/* If remaining length < VEC_SIZE.  */
+	addl	$VEC_SIZE, %edx
+	jle	L(zero_end)
 
-	VPCMPEQ (VEC_SIZE * 3)(%rdi), %ymm0, %ymm1
+	/* Check VEC2 and compare any match with
+	   remaining length.  */
+	VPCMPEQ	(VEC_SIZE + 1)(%rdi), %ymm0, %ymm1
 	vpmovmskb %ymm1, %eax
-	testl	%eax, %eax
-
-	jnz	L(first_vec_x3_check)
-	xorl	%eax, %eax
+	tzcntl	%eax, %eax
+	cmpl	%eax, %edx
+	jbe	L(set_zero_end)
+	addq	$(VEC_SIZE + 1), %rdi
+	addq	%rdi, %rax
+L(zero_end):
 	VZEROUPPER_RETURN
 
 	.p2align 4
-L(last_2x_vec):
-	addl	$(VEC_SIZE * 2), %edx
-	VPCMPEQ (%rdi), %ymm0, %ymm1
+L(loop_4x_vec_end):
+# endif
+	/* rawmemchr will fall through into this if match
+	   was found in loop.  */
+
 	vpmovmskb %ymm1, %eax
 	testl	%eax, %eax
+	jnz	L(last_vec_x1_return)
 
-	jnz	L(first_vec_x0_check)
-	subl	$VEC_SIZE, %edx
-	jle	L(zero)
-
-	VPCMPEQ VEC_SIZE(%rdi), %ymm0, %ymm1
-	vpmovmskb %ymm1, %eax
+	vpmovmskb %ymm2, %eax
 	testl	%eax, %eax
-	jnz	L(first_vec_x1_check)
-	xorl	%eax, %eax
-	VZEROUPPER_RETURN
+	jnz	L(last_vec_x2_return)
 
-	.p2align 4
-L(first_vec_x0_check):
-	tzcntl	%eax, %eax
-	/* Check the end of data.  */
-	cmpq	%rax, %rdx
-	jbe	L(zero)
+	vpmovmskb %ymm3, %eax
+	/* Combine VEC3 matches (eax) with VEC4 matches
+	   (ecx).  */
+	salq	$32, %rcx
+	orq	%rcx, %rax
+	tzcntq	%rax, %rax
+# ifdef USE_AS_RAWMEMCHR
+	subq	$(VEC_SIZE * 2 - 1), %rdi
+# else
+	subq	$-(VEC_SIZE * 2 + 1), %rdi
+# endif
 	addq	%rdi, %rax
 	VZEROUPPER_RETURN
+# ifndef USE_AS_RAWMEMCHR
 
 	.p2align 4
 L(first_vec_x1_check):
 	tzcntl	%eax, %eax
-	/* Check the end of data.  */
-	cmpq	%rax, %rdx
-	jbe	L(zero)
-	addq	$VEC_SIZE, %rax
+	/* Adjust length.  */
+	subl	$-(VEC_SIZE * 4), %edx
+	/* Check if match within remaining length.  */
+	cmpl	%eax, %edx
+	jbe	L(set_zero_end)
+	incq	%rdi
 	addq	%rdi, %rax
 	VZEROUPPER_RETURN
+	.p2align 4
+L(set_zero_end):
+	xorl	%eax, %eax
+	VZEROUPPER_RETURN
+# endif
 
 	.p2align 4
-L(first_vec_x2_check):
+L(last_vec_x1_return):
 	tzcntl	%eax, %eax
-	/* Check the end of data.  */
-	cmpq	%rax, %rdx
-	jbe	L(zero)
-	addq	$(VEC_SIZE * 2), %rax
+# ifdef USE_AS_RAWMEMCHR
+	subq	$(VEC_SIZE * 4 - 1), %rdi
+# else
+	incq	%rdi
+# endif
 	addq	%rdi, %rax
 	VZEROUPPER_RETURN
 
 	.p2align 4
-L(first_vec_x3_check):
+L(last_vec_x2_return):
 	tzcntl	%eax, %eax
-	/* Check the end of data.  */
-	cmpq	%rax, %rdx
-	jbe	L(zero)
-	addq	$(VEC_SIZE * 3), %rax
+# ifdef USE_AS_RAWMEMCHR
+	subq	$(VEC_SIZE * 3 - 1), %rdi
+# else
+	subq	$-(VEC_SIZE + 1), %rdi
+# endif
 	addq	%rdi, %rax
 	VZEROUPPER_RETURN
 
+# ifndef USE_AS_RAWMEMCHR
 	.p2align 4
-L(zero):
-	xorl	%eax, %eax
-	jmp     L(return_vzeroupper)
+L(last_4x_vec_or_less_cmpeq):
+	VPCMPEQ	(VEC_SIZE * 4 + 1)(%rdi), %ymm0, %ymm1
+	vpmovmskb %ymm1, %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	$(VEC_SIZE * 2), %edx
+	jle	L(last_2x_vec)
 	.p2align 4
-L(null):
-	xorl	%eax, %eax
-	ret
-# endif
+L(last_4x_vec):
+	VPCMPEQ	(VEC_SIZE + 1)(%rdi), %ymm0, %ymm1
+	vpmovmskb %ymm1, %eax
+	testl	%eax, %eax
+	jnz	L(last_vec_x2_return)
 
-	.p2align 4
-L(first_vec_x0):
-	tzcntl	%eax, %eax
-	addq	%rdi, %rax
-	VZEROUPPER_RETURN
+	VPCMPEQ	(VEC_SIZE * 2 + 1)(%rdi), %ymm0, %ymm1
+	vpmovmskb %ymm1, %eax
 
-	.p2align 4
-L(first_vec_x1):
-	tzcntl	%eax, %eax
-	addq	$VEC_SIZE, %rax
-	addq	%rdi, %rax
-	VZEROUPPER_RETURN
+	/* Create mask for possible matches within
+	   remaining length.  */
+	movq	$-1, %rcx
+	bzhiq	%rdx, %rcx, %rcx
 
-	.p2align 4
-L(first_vec_x2):
+	/* Test matches in data against length match.  */
+	andl	%ecx, %eax
+	jnz	L(last_vec_x3)
+
+	/* if remaining length <= VEC_SIZE * 3 (Note this
+	   is after remaining length was found to be > VEC_SIZE * 2.
+	 */
+	subl	$VEC_SIZE, %edx
+	jbe	L(zero_end2)
+
+	VPCMPEQ	(VEC_SIZE * 3 + 1)(%rdi), %ymm0, %ymm1
+	vpmovmskb %ymm1, %eax
+	/* Shift remaining length mask for last VEC.  */
+	shrq	$32, %rcx
+	andl	%ecx, %eax
+	jz	L(zero_end2)
 	tzcntl	%eax, %eax
-	addq	$(VEC_SIZE * 2), %rax
+	addq	$(VEC_SIZE * 3 + 1), %rdi
 	addq	%rdi, %rax
+L(zero_end2):
 	VZEROUPPER_RETURN
 
 	.p2align 4
-L(4x_vec_end):
-	vpmovmskb %ymm1, %eax
-	testl	%eax, %eax
-	jnz	L(first_vec_x0)
-	vpmovmskb %ymm2, %eax
-	testl	%eax, %eax
-	jnz	L(first_vec_x1)
-	vpmovmskb %ymm3, %eax
-	testl	%eax, %eax
-	jnz	L(first_vec_x2)
-	vpmovmskb %ymm4, %eax
-	testl	%eax, %eax
-L(first_vec_x3):
+L(last_vec_x3):
 	tzcntl	%eax, %eax
-	addq	$(VEC_SIZE * 3), %rax
+	subq	$-(VEC_SIZE * 2 + 1), %rdi
 	addq	%rdi, %rax
 	VZEROUPPER_RETURN
+# endif
 
-END (MEMCHR)
+END(MEMCHR)
 #endif