diff mbox series

[v4,1/2] x86: Optimize strlen-evex.S

Message ID 20210419184345.2576413-1-goldstein.w.n@gmail.com
State Superseded
Headers show
Series [v4,1/2] x86: Optimize strlen-evex.S | expand

Commit Message

Noah Goldstein April 19, 2021, 6:43 p.m. UTC
No bug. This commit optimizes strlen-evex.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-evex.S | 584 ++++++++++++++-----------
 1 file changed, 320 insertions(+), 264 deletions(-)

Comments

H.J. Lu April 19, 2021, 10:16 p.m. UTC | #1
On Mon, Apr 19, 2021 at 02:43:44PM -0400, Noah Goldstein wrote:
> No bug. This commit optimizes strlen-evex.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-evex.S | 584 ++++++++++++++-----------
>  1 file changed, 320 insertions(+), 264 deletions(-)
> 
> diff --git a/sysdeps/x86_64/multiarch/strlen-evex.S b/sysdeps/x86_64/multiarch/strlen-evex.S
> index 0583819078..36b28198c8 100644
> --- a/sysdeps/x86_64/multiarch/strlen-evex.S
> +++ b/sysdeps/x86_64/multiarch/strlen-evex.S
> @@ -29,11 +29,13 @@
>  # ifdef USE_AS_WCSLEN
>  #  define VPCMP		vpcmpd
>  #  define VPMINU	vpminud
> -#  define SHIFT_REG	r9d
> +#  define SHIFT_REG ecx
> +#  define CHAR_SIZE	4
>  # else
>  #  define VPCMP		vpcmpb
>  #  define VPMINU	vpminub
> -#  define SHIFT_REG	ecx
> +#  define SHIFT_REG edx
> +#  define CHAR_SIZE	1
>  # endif
>  
>  # define XMMZERO	xmm16
> @@ -46,132 +48,168 @@
>  # define YMM6		ymm22
>  
>  # define VEC_SIZE 32
> +# define PAGE_SIZE 4096
> +# define LOG_PAGE_SIZE 12
> +# define CHAR_PER_VEC (VEC_SIZE / CHAR_SIZE)
>  
>  	.section .text.evex,"ax",@progbits
>  ENTRY (STRLEN)
>  # ifdef USE_AS_STRNLEN
> -	/* Check for zero length.  */
> +	/* Check zero length.  */
>  	test	%RSI_LP, %RSI_LP
>  	jz	L(zero)
> -#  ifdef USE_AS_WCSLEN
> -	shl	$2, %RSI_LP
> -#  elif defined __ILP32__
> +#  ifdef __ILP32__
>  	/* Clear the upper 32 bits.  */
>  	movl	%esi, %esi
>  #  endif
>  	mov	%RSI_LP, %R8_LP
>  # endif
> -	movl	%edi, %ecx
> -	movq	%rdi, %rdx
> +	movl	%edi, %eax
>  	vpxorq	%XMMZERO, %XMMZERO, %XMMZERO
> -
> +	/* Shift left eax to clear all bits not relevant to page cross
> +	   check. This saves 2 bytes of code as opposed to using andl with
> +	   PAGE_SIZE - 1. Then compare with PAGE_SIZE - VEC_SIZE shifted
> +	   left by the same amount (an imm32 either way).  */
> +	sall	$(32 - LOG_PAGE_SIZE), %eax

I prefer AND over SAL for better throughput.


H.J.
---
>  	/* 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) << (32 - LOG_PAGE_SIZE)), %eax
> +	ja	L(cross_page_boundary)
>  
>  	/* Check the first VEC_SIZE bytes.  Each bit in K0 represents a
>  	   null byte.  */
>  	VPCMP	$0, (%rdi), %YMMZERO, %k0
>  	kmovd	%k0, %eax
> -	testl	%eax, %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 < CHAR_PER_VEC handle special.  */
> +	cmpq	$CHAR_PER_VEC, %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
> +	ret
>  # 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):
> +	/* Set bit for max len so that tzcnt will return min of max len
> +	   and position of first match.  */
> +	btsq	%rsi, %rax
> +	tzcntl	%eax, %eax
> +	ret
>  # endif
> -	jmp	L(more_4x_vec)
>  
>  	.p2align 4
> -L(cros_page_boundary):
> -	andl	$(VEC_SIZE - 1), %ecx
> -	andq	$-VEC_SIZE, %rdi
> -
> -# ifdef USE_AS_WCSLEN
> -	/* NB: Divide shift count by 4 since each bit in K0 represent 4
> -	   bytes.  */
> -	movl	%ecx, %SHIFT_REG
> -	sarl	$2, %SHIFT_REG
> +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
> +	/* Use ecx which was computed earlier to compute correct value.
> +	 */
> +	leal	-(CHAR_PER_VEC * 4 + 1)(%rcx, %rax), %eax
> +# else
> +	subl	%edx, %edi
> +#  ifdef USE_AS_WCSLEN
> +	/* NB: Divide bytes by 4 to get the wchar_t count.  */
> +	sarl	$2, %edi
> +#  endif
> +	leal	CHAR_PER_VEC(%rdi, %rax), %eax
>  # endif
> -	VPCMP	$0, (%rdi), %YMMZERO, %k0
> -	kmovd	%k0, %eax
> +	ret
>  
> -	/* Remove the leading bytes.  */
> -	sarxl	%SHIFT_REG, %eax, %eax
> -	testl	%eax, %eax
> -	jz	L(aligned_more)
> +	.p2align 4
> +L(first_vec_x2):
>  	tzcntl	%eax, %eax
> -# ifdef USE_AS_WCSLEN
> -	/* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> -	sall	$2, %eax
> -# endif
> +	/* 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)
> -# endif
> -	addq	%rdi, %rax
> -	addq	%rcx, %rax
> -	subq	%rdx, %rax
> -# ifdef USE_AS_WCSLEN
> -	shrq	$2, %rax
> +	/* Use ecx which was computed earlier to compute correct value.
> +	 */
> +	leal	-(CHAR_PER_VEC * 3 + 1)(%rcx, %rax), %eax
> +# else
> +	subl	%edx, %edi
> +#  ifdef USE_AS_WCSLEN
> +	/* NB: Divide bytes by 4 to get the wchar_t count.  */
> +	sarl	$2, %edi
> +#  endif
> +	leal	(CHAR_PER_VEC * 2)(%rdi, %rax), %eax
>  # endif
>  	ret
>  
>  	.p2align 4
> -L(aligned_more):
> +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
> -        /* "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.
> +	 */
> +	leal	-(CHAR_PER_VEC * 2 + 1)(%rcx, %rax), %eax
> +# else
> +	subl	%edx, %edi
> +#  ifdef USE_AS_WCSLEN
> +	/* NB: Divide bytes by 4 to get the wchar_t count.  */
> +	sarl	$2, %edi
> +#  endif
> +	leal	(CHAR_PER_VEC * 3)(%rdi, %rax), %eax
>  # endif
> +	ret
>  
> -	addq	$VEC_SIZE, %rdi
> -
> +	.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.
> +	 */
> +	leal	-(CHAR_PER_VEC + 1)(%rcx, %rax), %eax
> +# else
> +	subl	%edx, %edi
> +#  ifdef USE_AS_WCSLEN
> +	/* NB: Divide bytes by 4 to get the wchar_t count.  */
> +	sarl	$2, %edi
> +#  endif
> +	leal	(CHAR_PER_VEC * 4)(%rdi, %rax), %eax
>  # endif
> +	ret
>  
> -L(more_4x_vec):
> +	.p2align 5
> +L(aligned_more):
> +	movq	%rdi, %rdx
> +	/* Align data to VEC_SIZE.  */
> +	andq	$-(VEC_SIZE), %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.  */
> -	VPCMP	$0, (%rdi), %YMMZERO, %k0
> -	kmovd	%k0, %eax
> -	testl	%eax, %eax
> -	jnz	L(first_vec_x0)
> -
> +# ifdef USE_AS_STRNLEN
> +	/* + CHAR_SIZE because it simplies the logic in
> +	   last_4x_vec_or_less.  */
> +	leaq	(VEC_SIZE * 5 + CHAR_SIZE)(%rdi), %rcx
> +	subq	%rdx, %rcx
> +#  ifdef USE_AS_WCSLEN
> +	/* NB: Divide bytes by 4 to get the wchar_t count.  */
> +	sarl	$2, %ecx
> +#  endif
> +# endif
> +	/* Load first VEC regardless.  */
>  	VPCMP	$0, VEC_SIZE(%rdi), %YMMZERO, %k0
> +# ifdef USE_AS_STRNLEN
> +	/* Adjust length. If near end handle specially.  */
> +	subq	%rcx, %rsi
> +	jb	L(last_4x_vec_or_less)
> +# endif
>  	kmovd	%k0, %eax
>  	testl	%eax, %eax
>  	jnz	L(first_vec_x1)
>  
>  	VPCMP	$0, (VEC_SIZE * 2)(%rdi), %YMMZERO, %k0
>  	kmovd	%k0, %eax
> -	testl	%eax, %eax
> +	test	%eax, %eax
>  	jnz	L(first_vec_x2)
>  
>  	VPCMP	$0, (VEC_SIZE * 3)(%rdi), %YMMZERO, %k0
> @@ -179,258 +217,276 @@ L(more_4x_vec):
>  	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
> +	VPCMP	$0, (VEC_SIZE * 4)(%rdi), %YMMZERO, %k0
> +	kmovd	%k0, %eax
> +	testl	%eax, %eax
> +	jnz	L(first_vec_x4)
>  
> +	addq	$VEC_SIZE, %rdi
>  # ifdef USE_AS_STRNLEN
> -	/* Adjust length.  */
> +	/* Check if at last VEC_SIZE * 4 length.  */
> +	cmpq	$(CHAR_PER_VEC * 4 - 1), %rsi
> +	jbe	L(last_4x_vec_or_less_load)
> +	movl	%edi, %ecx
> +	andl	$(VEC_SIZE * 4 - 1), %ecx
> +#  ifdef USE_AS_WCSLEN
> +	/* NB: Divide bytes by 4 to get the wchar_t count.  */
> +	sarl	$2, %ecx
> +#  endif
> +	/* Readjust length.  */
>  	addq	%rcx, %rsi
>  # endif
> +	/* Align data to VEC_SIZE * 4.  */
> +	andq	$-(VEC_SIZE * 4), %rdi
>  
> +	/* Compare 4 * VEC at a time forward.  */
>  	.p2align 4
>  L(loop_4x_vec):
> -	/* Compare 4 * VEC at a time forward.  */
> -	VMOVA	(%rdi), %YMM1
> -	VMOVA	VEC_SIZE(%rdi), %YMM2
> -	VMOVA	(VEC_SIZE * 2)(%rdi), %YMM3
> -	VMOVA	(VEC_SIZE * 3)(%rdi), %YMM4
> -
> -	VPMINU	%YMM1, %YMM2, %YMM5
> -	VPMINU	%YMM3, %YMM4, %YMM6
> +	/* Load first VEC regardless.  */
> +	VMOVA	(VEC_SIZE * 4)(%rdi), %YMM1
> +# ifdef USE_AS_STRNLEN
> +	/* Break if at end of length.  */
> +	subq	$(CHAR_PER_VEC * 4), %rsi
> +	jb	L(last_4x_vec_or_less_cmpeq)
> +# endif
> +	/* Save some code size by microfusing VPMINU with the load. Since
> +	   the matches in ymm2/ymm4 can only be returned if there where no
> +	   matches in ymm1/ymm3 respectively there is no issue with overlap.
> +	 */
> +	VPMINU	(VEC_SIZE * 5)(%rdi), %YMM1, %YMM2
> +	VMOVA	(VEC_SIZE * 6)(%rdi), %YMM3
> +	VPMINU	(VEC_SIZE * 7)(%rdi), %YMM3, %YMM4
> +
> +	VPCMP	$0, %YMM2, %YMMZERO, %k0
> +	VPCMP	$0, %YMM4, %YMMZERO, %k1
> +	subq	$-(VEC_SIZE * 4), %rdi
> +	kortestd	%k0, %k1
> +	jz	L(loop_4x_vec)
> +
> +	/* Check if end was in first half.  */
> +	kmovd	%k0, %eax
> +	subq	%rdx, %rdi
> +# ifdef USE_AS_WCSLEN
> +	shrq	$2, %rdi
> +# endif
> +	testl	%eax, %eax
> +	jz	L(second_vec_return)
>  
> -	VPMINU	%YMM5, %YMM6, %YMM5
> -	VPCMP	$0, %YMM5, %YMMZERO, %k0
> -	ktestd	%k0, %k0
> -	jnz	L(4x_vec_end)
> +	VPCMP	$0, %YMM1, %YMMZERO, %k2
> +	kmovd	%k2, %edx
> +	/* Combine VEC1 matches (edx) with VEC2 matches (eax).  */
> +# ifdef USE_AS_WCSLEN
> +	sall	$CHAR_PER_VEC, %eax
> +	orl	%edx, %eax
> +	tzcntl	%eax, %eax
> +# else
> +	salq	$CHAR_PER_VEC, %rax
> +	orq	%rdx, %rax
> +	tzcntq	%rax, %rax
> +# endif
> +	addq	%rdi, %rax
> +	ret
>  
> -	addq	$(VEC_SIZE * 4), %rdi
>  
> -# ifndef USE_AS_STRNLEN
> -	jmp	L(loop_4x_vec)
> -# else
> -	subq	$(VEC_SIZE * 4), %rsi
> -	ja	L(loop_4x_vec)
> +# ifdef USE_AS_STRNLEN
>  
> +L(last_4x_vec_or_less_load):
> +	/* Depending on entry adjust rdi / prepare first VEC in YMM1.  */
> +	VMOVA	(VEC_SIZE * 4)(%rdi), %YMM1
> +L(last_4x_vec_or_less_cmpeq):
> +	VPCMP	$0, %YMM1, %YMMZERO, %k0
> +	addq	$(VEC_SIZE * 3), %rdi
>  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)
> -
> -	VPCMP	$0, (%rdi), %YMMZERO, %k0
>  	kmovd	%k0, %eax
> +	/* If remaining length > VEC_SIZE * 2. This works if esi is off by
> +	   VEC_SIZE * 4.  */
> +	testl	$(CHAR_PER_VEC * 2), %esi
> +	jnz	L(last_4x_vec)
> +
> +	/* length may have been negative or positive by an offset of
> +	   CHAR_PER_VEC * 4 depending on where this was called from. This
> +	   fixes that.  */
> +	andl	$(CHAR_PER_VEC * 4 - 1), %esi
>  	testl	%eax, %eax
> -	jnz	L(first_vec_x0)
> +	jnz	L(last_vec_x1_check)
>  
> -	VPCMP	$0, VEC_SIZE(%rdi), %YMMZERO, %k0
> -	kmovd	%k0, %eax
> -	testl	%eax, %eax
> -	jnz	L(first_vec_x1)
> +	/* Check the end of data.  */
> +	subl	$CHAR_PER_VEC, %esi
> +	jb	L(max)
>  
>  	VPCMP	$0, (VEC_SIZE * 2)(%rdi), %YMMZERO, %k0
>  	kmovd	%k0, %eax
> -	testl	%eax, %eax
> -	jnz	L(first_vec_x2_check)
> -	subl	$VEC_SIZE, %esi
> -	jle	L(max)
> +	tzcntl	%eax, %eax
> +	/* Check the end of data.  */
> +	cmpl	%eax, %esi
> +	jb	L(max)
>  
> -	VPCMP	$0, (VEC_SIZE * 3)(%rdi), %YMMZERO, %k0
> -	kmovd	%k0, %eax
> -	testl	%eax, %eax
> -	jnz	L(first_vec_x3_check)
> +	subq	%rdx, %rdi
> +#  ifdef USE_AS_WCSLEN
> +	/* NB: Divide bytes by 4 to get the wchar_t count.  */
> +	sarq	$2, %rdi
> +#  endif
> +	leaq	(CHAR_PER_VEC * 2)(%rdi, %rax), %rax
> +	ret
> +L(max):
>  	movq	%r8, %rax
> +	ret
> +# endif
> +
> +	/* Placed here in strnlen so that the jcc L(last_4x_vec_or_less)
> +	   in the 4x VEC loop can use 2 byte encoding.  */
> +	.p2align 4
> +L(second_vec_return):
> +	VPCMP	$0, %YMM3, %YMMZERO, %k0
> +	/* Combine YMM3 matches (k0) with YMM4 matches (k1).  */
> +# ifdef USE_AS_WCSLEN
> +	kunpckbw	%k0, %k1, %k0
> +	kmovd	%k0, %eax
> +	tzcntl	%eax, %eax
> +# else
> +	kunpckdq	%k0, %k1, %k0
> +	kmovq	%k0, %rax
> +	tzcntq	%rax, %rax
> +# endif
> +	leaq	(CHAR_PER_VEC * 2)(%rdi, %rax), %rax
> +	ret
> +
> +
> +# ifdef USE_AS_STRNLEN
> +L(last_vec_x1_check):
> +	tzcntl	%eax, %eax
> +	/* Check the end of data.  */
> +	cmpl	%eax, %esi
> +	jb	L(max)
> +	subq	%rdx, %rdi
>  #  ifdef USE_AS_WCSLEN
> -	shrq	$2, %rax
> +	/* NB: Divide bytes by 4 to get the wchar_t count.  */
> +	sarq	$2, %rdi
>  #  endif
> +	leaq	(CHAR_PER_VEC)(%rdi, %rax), %rax
>  	ret
>  
>  	.p2align 4
> -L(last_2x_vec):
> -	addl	$(VEC_SIZE * 2), %esi
> +L(last_4x_vec):
> +	/* Test first 2x VEC normally.  */
> +	testl	%eax, %eax
> +	jnz	L(last_vec_x1)
>  
> -	VPCMP	$0, (%rdi), %YMMZERO, %k0
> +	VPCMP	$0, (VEC_SIZE * 2)(%rdi), %YMMZERO, %k0
>  	kmovd	%k0, %eax
>  	testl	%eax, %eax
> -	jnz	L(first_vec_x0_check)
> -	subl	$VEC_SIZE, %esi
> -	jle	L(max)
> +	jnz	L(last_vec_x2)
>  
> -	VPCMP	$0, VEC_SIZE(%rdi), %YMMZERO, %k0
> +	/* Normalize length.  */
> +	andl	$(CHAR_PER_VEC * 4 - 1), %esi
> +	VPCMP	$0, (VEC_SIZE * 3)(%rdi), %YMMZERO, %k0
>  	kmovd	%k0, %eax
>  	testl	%eax, %eax
> -	jnz	L(first_vec_x1_check)
> -	movq	%r8, %rax
> -#  ifdef USE_AS_WCSLEN
> -	shrq	$2, %rax
> -#  endif
> -	ret
> +	jnz	L(last_vec_x3)
>  
> -	.p2align 4
> -L(first_vec_x0_check):
> +	/* Check the end of data.  */
> +	subl	$(CHAR_PER_VEC * 3), %esi
> +	jb	L(max)
> +
> +	VPCMP	$0, (VEC_SIZE * 4)(%rdi), %YMMZERO, %k0
> +	kmovd	%k0, %eax
>  	tzcntl	%eax, %eax
> -#  ifdef USE_AS_WCSLEN
> -	/* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> -	sall	$2, %eax
> -#  endif
>  	/* Check the end of data.  */
> -	cmpq	%rax, %rsi
> -	jbe	L(max)
> -	addq	%rdi, %rax
> -	subq	%rdx, %rax
> +	cmpl	%eax, %esi
> +	jb	L(max_end)
> +
> +	subq	%rdx, %rdi
>  #  ifdef USE_AS_WCSLEN
> -	shrq	$2, %rax
> +	/* NB: Divide bytes by 4 to get the wchar_t count.  */
> +	sarq	$2, %rdi
>  #  endif
> +	leaq	(CHAR_PER_VEC * 4)(%rdi, %rax), %rax
>  	ret
>  
>  	.p2align 4
> -L(first_vec_x1_check):
> +L(last_vec_x1):
>  	tzcntl	%eax, %eax
> +	subq	%rdx, %rdi
>  #  ifdef USE_AS_WCSLEN
> -	/* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> -	sall	$2, %eax
> -#  endif
> -	/* Check the end of data.  */
> -	cmpq	%rax, %rsi
> -	jbe	L(max)
> -	addq	$VEC_SIZE, %rax
> -	addq	%rdi, %rax
> -	subq	%rdx, %rax
> -#  ifdef USE_AS_WCSLEN
> -	shrq	$2, %rax
> +	/* NB: Divide bytes by 4 to get the wchar_t count.  */
> +	sarq	$2, %rdi
>  #  endif
> +	leaq	(CHAR_PER_VEC)(%rdi, %rax), %rax
>  	ret
>  
>  	.p2align 4
> -L(first_vec_x2_check):
> +L(last_vec_x2):
>  	tzcntl	%eax, %eax
> +	subq	%rdx, %rdi
>  #  ifdef USE_AS_WCSLEN
> -	/* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> -	sall	$2, %eax
> -#  endif
> -	/* Check the end of data.  */
> -	cmpq	%rax, %rsi
> -	jbe	L(max)
> -	addq	$(VEC_SIZE * 2), %rax
> -	addq	%rdi, %rax
> -	subq	%rdx, %rax
> -#  ifdef USE_AS_WCSLEN
> -	shrq	$2, %rax
> +	/* NB: Divide bytes by 4 to get the wchar_t count.  */
> +	sarq	$2, %rdi
>  #  endif
> +	leaq	(CHAR_PER_VEC * 2)(%rdi, %rax), %rax
>  	ret
>  
>  	.p2align 4
> -L(first_vec_x3_check):
> +L(last_vec_x3):
>  	tzcntl	%eax, %eax
> -#  ifdef USE_AS_WCSLEN
> -	/* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> -	sall	$2, %eax
> -#  endif
> +	subl	$(CHAR_PER_VEC * 2), %esi
>  	/* Check the end of data.  */
> -	cmpq	%rax, %rsi
> -	jbe	L(max)
> -	addq	$(VEC_SIZE * 3), %rax
> -	addq	%rdi, %rax
> -	subq	%rdx, %rax
> +	cmpl	%eax, %esi
> +	jb	L(max_end)
> +	subq	%rdx, %rdi
>  #  ifdef USE_AS_WCSLEN
> -	shrq	$2, %rax
> +	/* NB: Divide bytes by 4 to get the wchar_t count.  */
> +	sarq	$2, %rdi
>  #  endif
> +	leaq	(CHAR_PER_VEC * 3)(%rdi, %rax), %rax
>  	ret
> -
> -	.p2align 4
> -L(max):
> +L(max_end):
>  	movq	%r8, %rax
> -#  ifdef USE_AS_WCSLEN
> -	shrq	$2, %rax
> -#  endif
> -	ret
> -
> -	.p2align 4
> -L(zero):
> -	xorl	%eax, %eax
>  	ret
>  # endif
>  
> +	/* Cold case for crossing page with first load.	 */
>  	.p2align 4
> -L(first_vec_x0):
> -	tzcntl	%eax, %eax
> -# ifdef USE_AS_WCSLEN
> -	/* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> -	sall	$2, %eax
> -# endif
> -	addq	%rdi, %rax
> -	subq	%rdx, %rax
> +L(cross_page_boundary):
> +	movq	%rdi, %rdx
> +	/* Align data to VEC_SIZE.  */
> +	andq	$-VEC_SIZE, %rdi
> +	VPCMP	$0, (%rdi), %YMMZERO, %k0
> +	kmovd	%k0, %eax
> +	/* Remove the leading bytes.  */
>  # ifdef USE_AS_WCSLEN
> -	shrq	$2, %rax
> +	/* NB: Divide shift count by 4 since each bit in K0 represent 4
> +	   bytes.  */
> +	movl	%edx, %ecx
> +	shrl	$2, %ecx
> +	andl	$(CHAR_PER_VEC - 1), %ecx
>  # endif
> -	ret
> -
> -	.p2align 4
> -L(first_vec_x1):
> +	/* SHIFT_REG is ecx for USE_AS_WCSLEN and edx otherwise.  */
> +	sarxl	%SHIFT_REG, %eax, %eax
> +	testl	%eax, %eax
> +# ifndef USE_AS_STRNLEN
> +	jz	L(cross_page_continue)
>  	tzcntl	%eax, %eax
> -# ifdef USE_AS_WCSLEN
> -	/* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> -	sall	$2, %eax
> -# endif
> -	addq	$VEC_SIZE, %rax
> -	addq	%rdi, %rax
> -	subq	%rdx, %rax
> -# ifdef USE_AS_WCSLEN
> -	shrq	$2, %rax
> -# endif
>  	ret
> -
> -	.p2align 4
> -L(first_vec_x2):
> -	tzcntl	%eax, %eax
> -# ifdef USE_AS_WCSLEN
> -	/* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> -	sall	$2, %eax
> -# endif
> -	addq	$(VEC_SIZE * 2), %rax
> -	addq	%rdi, %rax
> -	subq	%rdx, %rax
> -# ifdef USE_AS_WCSLEN
> -	shrq	$2, %rax
> -# endif
> +# else
> +	jnz	L(cross_page_less_vec)
> +#  ifndef USE_AS_WCSLEN
> +	movl	%edx, %ecx
> +	andl	$(CHAR_PER_VEC - 1), %ecx
> +#  endif
> +	movl	$CHAR_PER_VEC, %eax
> +	subl	%ecx, %eax
> +	/* Check the end of data.  */
> +	cmpq	%rax, %rsi
> +	ja	L(cross_page_continue)
> +	movl	%esi, %eax
>  	ret
> -
> -	.p2align 4
> -L(4x_vec_end):
> -	VPCMP	$0, %YMM1, %YMMZERO, %k0
> -	kmovd	%k0, %eax
> -	testl	%eax, %eax
> -	jnz	L(first_vec_x0)
> -	VPCMP	$0, %YMM2, %YMMZERO, %k1
> -	kmovd	%k1, %eax
> -	testl	%eax, %eax
> -	jnz	L(first_vec_x1)
> -	VPCMP	$0, %YMM3, %YMMZERO, %k2
> -	kmovd	%k2, %eax
> -	testl	%eax, %eax
> -	jnz	L(first_vec_x2)
> -	VPCMP	$0, %YMM4, %YMMZERO, %k3
> -	kmovd	%k3, %eax
> -L(first_vec_x3):
> +L(cross_page_less_vec):
>  	tzcntl	%eax, %eax
> -# ifdef USE_AS_WCSLEN
> -	/* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> -	sall	$2, %eax
> -# endif
> -	addq	$(VEC_SIZE * 3), %rax
> -	addq	%rdi, %rax
> -	subq	%rdx, %rax
> -# ifdef USE_AS_WCSLEN
> -	shrq	$2, %rax
> -# endif
> +	/* Select min of length and position of first null.  */
> +	cmpq	%rax, %rsi
> +	cmovb	%esi, %eax
>  	ret
> +# endif
>  
>  END (STRLEN)
>  #endif
> -- 
> 2.29.2
>
Noah Goldstein April 19, 2021, 11:38 p.m. UTC | #2
On Mon, Apr 19, 2021 at 6:16 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Mon, Apr 19, 2021 at 02:43:44PM -0400, Noah Goldstein wrote:
> > No bug. This commit optimizes strlen-evex.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-evex.S | 584 ++++++++++++++-----------
> >  1 file changed, 320 insertions(+), 264 deletions(-)
> >
> > diff --git a/sysdeps/x86_64/multiarch/strlen-evex.S b/sysdeps/x86_64/multiarch/strlen-evex.S
> > index 0583819078..36b28198c8 100644
> > --- a/sysdeps/x86_64/multiarch/strlen-evex.S
> > +++ b/sysdeps/x86_64/multiarch/strlen-evex.S
> > @@ -29,11 +29,13 @@
> >  # ifdef USE_AS_WCSLEN
> >  #  define VPCMP              vpcmpd
> >  #  define VPMINU     vpminud
> > -#  define SHIFT_REG  r9d
> > +#  define SHIFT_REG ecx
> > +#  define CHAR_SIZE  4
> >  # else
> >  #  define VPCMP              vpcmpb
> >  #  define VPMINU     vpminub
> > -#  define SHIFT_REG  ecx
> > +#  define SHIFT_REG edx
> > +#  define CHAR_SIZE  1
> >  # endif
> >
> >  # define XMMZERO     xmm16
> > @@ -46,132 +48,168 @@
> >  # define YMM6                ymm22
> >
> >  # define VEC_SIZE 32
> > +# define PAGE_SIZE 4096
> > +# define LOG_PAGE_SIZE 12
> > +# define CHAR_PER_VEC (VEC_SIZE / CHAR_SIZE)
> >
> >       .section .text.evex,"ax",@progbits
> >  ENTRY (STRLEN)
> >  # ifdef USE_AS_STRNLEN
> > -     /* Check for zero length.  */
> > +     /* Check zero length.  */
> >       test    %RSI_LP, %RSI_LP
> >       jz      L(zero)
> > -#  ifdef USE_AS_WCSLEN
> > -     shl     $2, %RSI_LP
> > -#  elif defined __ILP32__
> > +#  ifdef __ILP32__
> >       /* Clear the upper 32 bits.  */
> >       movl    %esi, %esi
> >  #  endif
> >       mov     %RSI_LP, %R8_LP
> >  # endif
> > -     movl    %edi, %ecx
> > -     movq    %rdi, %rdx
> > +     movl    %edi, %eax
> >       vpxorq  %XMMZERO, %XMMZERO, %XMMZERO
> > -
> > +     /* Shift left eax to clear all bits not relevant to page cross
> > +        check. This saves 2 bytes of code as opposed to using andl with
> > +        PAGE_SIZE - 1. Then compare with PAGE_SIZE - VEC_SIZE shifted
> > +        left by the same amount (an imm32 either way).  */
> > +     sall    $(32 - LOG_PAGE_SIZE), %eax
>
> I prefer AND over SAL for better throughput.

Done.

>
>
> H.J.
> ---
> >       /* 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) << (32 - LOG_PAGE_SIZE)), %eax
> > +     ja      L(cross_page_boundary)
> >
> >       /* Check the first VEC_SIZE bytes.  Each bit in K0 represents a
> >          null byte.  */
> >       VPCMP   $0, (%rdi), %YMMZERO, %k0
> >       kmovd   %k0, %eax
> > -     testl   %eax, %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 < CHAR_PER_VEC handle special.  */
> > +     cmpq    $CHAR_PER_VEC, %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
> > +     ret
> >  # 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):
> > +     /* Set bit for max len so that tzcnt will return min of max len
> > +        and position of first match.  */
> > +     btsq    %rsi, %rax
> > +     tzcntl  %eax, %eax
> > +     ret
> >  # endif
> > -     jmp     L(more_4x_vec)
> >
> >       .p2align 4
> > -L(cros_page_boundary):
> > -     andl    $(VEC_SIZE - 1), %ecx
> > -     andq    $-VEC_SIZE, %rdi
> > -
> > -# ifdef USE_AS_WCSLEN
> > -     /* NB: Divide shift count by 4 since each bit in K0 represent 4
> > -        bytes.  */
> > -     movl    %ecx, %SHIFT_REG
> > -     sarl    $2, %SHIFT_REG
> > +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
> > +     /* Use ecx which was computed earlier to compute correct value.
> > +      */
> > +     leal    -(CHAR_PER_VEC * 4 + 1)(%rcx, %rax), %eax
> > +# else
> > +     subl    %edx, %edi
> > +#  ifdef USE_AS_WCSLEN
> > +     /* NB: Divide bytes by 4 to get the wchar_t count.  */
> > +     sarl    $2, %edi
> > +#  endif
> > +     leal    CHAR_PER_VEC(%rdi, %rax), %eax
> >  # endif
> > -     VPCMP   $0, (%rdi), %YMMZERO, %k0
> > -     kmovd   %k0, %eax
> > +     ret
> >
> > -     /* Remove the leading bytes.  */
> > -     sarxl   %SHIFT_REG, %eax, %eax
> > -     testl   %eax, %eax
> > -     jz      L(aligned_more)
> > +     .p2align 4
> > +L(first_vec_x2):
> >       tzcntl  %eax, %eax
> > -# ifdef USE_AS_WCSLEN
> > -     /* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> > -     sall    $2, %eax
> > -# endif
> > +     /* 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)
> > -# endif
> > -     addq    %rdi, %rax
> > -     addq    %rcx, %rax
> > -     subq    %rdx, %rax
> > -# ifdef USE_AS_WCSLEN
> > -     shrq    $2, %rax
> > +     /* Use ecx which was computed earlier to compute correct value.
> > +      */
> > +     leal    -(CHAR_PER_VEC * 3 + 1)(%rcx, %rax), %eax
> > +# else
> > +     subl    %edx, %edi
> > +#  ifdef USE_AS_WCSLEN
> > +     /* NB: Divide bytes by 4 to get the wchar_t count.  */
> > +     sarl    $2, %edi
> > +#  endif
> > +     leal    (CHAR_PER_VEC * 2)(%rdi, %rax), %eax
> >  # endif
> >       ret
> >
> >       .p2align 4
> > -L(aligned_more):
> > +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
> > -        /* "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.
> > +      */
> > +     leal    -(CHAR_PER_VEC * 2 + 1)(%rcx, %rax), %eax
> > +# else
> > +     subl    %edx, %edi
> > +#  ifdef USE_AS_WCSLEN
> > +     /* NB: Divide bytes by 4 to get the wchar_t count.  */
> > +     sarl    $2, %edi
> > +#  endif
> > +     leal    (CHAR_PER_VEC * 3)(%rdi, %rax), %eax
> >  # endif
> > +     ret
> >
> > -     addq    $VEC_SIZE, %rdi
> > -
> > +     .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.
> > +      */
> > +     leal    -(CHAR_PER_VEC + 1)(%rcx, %rax), %eax
> > +# else
> > +     subl    %edx, %edi
> > +#  ifdef USE_AS_WCSLEN
> > +     /* NB: Divide bytes by 4 to get the wchar_t count.  */
> > +     sarl    $2, %edi
> > +#  endif
> > +     leal    (CHAR_PER_VEC * 4)(%rdi, %rax), %eax
> >  # endif
> > +     ret
> >
> > -L(more_4x_vec):
> > +     .p2align 5
> > +L(aligned_more):
> > +     movq    %rdi, %rdx
> > +     /* Align data to VEC_SIZE.  */
> > +     andq    $-(VEC_SIZE), %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.  */
> > -     VPCMP   $0, (%rdi), %YMMZERO, %k0
> > -     kmovd   %k0, %eax
> > -     testl   %eax, %eax
> > -     jnz     L(first_vec_x0)
> > -
> > +# ifdef USE_AS_STRNLEN
> > +     /* + CHAR_SIZE because it simplies the logic in
> > +        last_4x_vec_or_less.  */
> > +     leaq    (VEC_SIZE * 5 + CHAR_SIZE)(%rdi), %rcx
> > +     subq    %rdx, %rcx
> > +#  ifdef USE_AS_WCSLEN
> > +     /* NB: Divide bytes by 4 to get the wchar_t count.  */
> > +     sarl    $2, %ecx
> > +#  endif
> > +# endif
> > +     /* Load first VEC regardless.  */
> >       VPCMP   $0, VEC_SIZE(%rdi), %YMMZERO, %k0
> > +# ifdef USE_AS_STRNLEN
> > +     /* Adjust length. If near end handle specially.  */
> > +     subq    %rcx, %rsi
> > +     jb      L(last_4x_vec_or_less)
> > +# endif
> >       kmovd   %k0, %eax
> >       testl   %eax, %eax
> >       jnz     L(first_vec_x1)
> >
> >       VPCMP   $0, (VEC_SIZE * 2)(%rdi), %YMMZERO, %k0
> >       kmovd   %k0, %eax
> > -     testl   %eax, %eax
> > +     test    %eax, %eax
> >       jnz     L(first_vec_x2)
> >
> >       VPCMP   $0, (VEC_SIZE * 3)(%rdi), %YMMZERO, %k0
> > @@ -179,258 +217,276 @@ L(more_4x_vec):
> >       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
> > +     VPCMP   $0, (VEC_SIZE * 4)(%rdi), %YMMZERO, %k0
> > +     kmovd   %k0, %eax
> > +     testl   %eax, %eax
> > +     jnz     L(first_vec_x4)
> >
> > +     addq    $VEC_SIZE, %rdi
> >  # ifdef USE_AS_STRNLEN
> > -     /* Adjust length.  */
> > +     /* Check if at last VEC_SIZE * 4 length.  */
> > +     cmpq    $(CHAR_PER_VEC * 4 - 1), %rsi
> > +     jbe     L(last_4x_vec_or_less_load)
> > +     movl    %edi, %ecx
> > +     andl    $(VEC_SIZE * 4 - 1), %ecx
> > +#  ifdef USE_AS_WCSLEN
> > +     /* NB: Divide bytes by 4 to get the wchar_t count.  */
> > +     sarl    $2, %ecx
> > +#  endif
> > +     /* Readjust length.  */
> >       addq    %rcx, %rsi
> >  # endif
> > +     /* Align data to VEC_SIZE * 4.  */
> > +     andq    $-(VEC_SIZE * 4), %rdi
> >
> > +     /* Compare 4 * VEC at a time forward.  */
> >       .p2align 4
> >  L(loop_4x_vec):
> > -     /* Compare 4 * VEC at a time forward.  */
> > -     VMOVA   (%rdi), %YMM1
> > -     VMOVA   VEC_SIZE(%rdi), %YMM2
> > -     VMOVA   (VEC_SIZE * 2)(%rdi), %YMM3
> > -     VMOVA   (VEC_SIZE * 3)(%rdi), %YMM4
> > -
> > -     VPMINU  %YMM1, %YMM2, %YMM5
> > -     VPMINU  %YMM3, %YMM4, %YMM6
> > +     /* Load first VEC regardless.  */
> > +     VMOVA   (VEC_SIZE * 4)(%rdi), %YMM1
> > +# ifdef USE_AS_STRNLEN
> > +     /* Break if at end of length.  */
> > +     subq    $(CHAR_PER_VEC * 4), %rsi
> > +     jb      L(last_4x_vec_or_less_cmpeq)
> > +# endif
> > +     /* Save some code size by microfusing VPMINU with the load. Since
> > +        the matches in ymm2/ymm4 can only be returned if there where no
> > +        matches in ymm1/ymm3 respectively there is no issue with overlap.
> > +      */
> > +     VPMINU  (VEC_SIZE * 5)(%rdi), %YMM1, %YMM2
> > +     VMOVA   (VEC_SIZE * 6)(%rdi), %YMM3
> > +     VPMINU  (VEC_SIZE * 7)(%rdi), %YMM3, %YMM4
> > +
> > +     VPCMP   $0, %YMM2, %YMMZERO, %k0
> > +     VPCMP   $0, %YMM4, %YMMZERO, %k1
> > +     subq    $-(VEC_SIZE * 4), %rdi
> > +     kortestd        %k0, %k1
> > +     jz      L(loop_4x_vec)
> > +
> > +     /* Check if end was in first half.  */
> > +     kmovd   %k0, %eax
> > +     subq    %rdx, %rdi
> > +# ifdef USE_AS_WCSLEN
> > +     shrq    $2, %rdi
> > +# endif
> > +     testl   %eax, %eax
> > +     jz      L(second_vec_return)
> >
> > -     VPMINU  %YMM5, %YMM6, %YMM5
> > -     VPCMP   $0, %YMM5, %YMMZERO, %k0
> > -     ktestd  %k0, %k0
> > -     jnz     L(4x_vec_end)
> > +     VPCMP   $0, %YMM1, %YMMZERO, %k2
> > +     kmovd   %k2, %edx
> > +     /* Combine VEC1 matches (edx) with VEC2 matches (eax).  */
> > +# ifdef USE_AS_WCSLEN
> > +     sall    $CHAR_PER_VEC, %eax
> > +     orl     %edx, %eax
> > +     tzcntl  %eax, %eax
> > +# else
> > +     salq    $CHAR_PER_VEC, %rax
> > +     orq     %rdx, %rax
> > +     tzcntq  %rax, %rax
> > +# endif
> > +     addq    %rdi, %rax
> > +     ret
> >
> > -     addq    $(VEC_SIZE * 4), %rdi
> >
> > -# ifndef USE_AS_STRNLEN
> > -     jmp     L(loop_4x_vec)
> > -# else
> > -     subq    $(VEC_SIZE * 4), %rsi
> > -     ja      L(loop_4x_vec)
> > +# ifdef USE_AS_STRNLEN
> >
> > +L(last_4x_vec_or_less_load):
> > +     /* Depending on entry adjust rdi / prepare first VEC in YMM1.  */
> > +     VMOVA   (VEC_SIZE * 4)(%rdi), %YMM1
> > +L(last_4x_vec_or_less_cmpeq):
> > +     VPCMP   $0, %YMM1, %YMMZERO, %k0
> > +     addq    $(VEC_SIZE * 3), %rdi
> >  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)
> > -
> > -     VPCMP   $0, (%rdi), %YMMZERO, %k0
> >       kmovd   %k0, %eax
> > +     /* If remaining length > VEC_SIZE * 2. This works if esi is off by
> > +        VEC_SIZE * 4.  */
> > +     testl   $(CHAR_PER_VEC * 2), %esi
> > +     jnz     L(last_4x_vec)
> > +
> > +     /* length may have been negative or positive by an offset of
> > +        CHAR_PER_VEC * 4 depending on where this was called from. This
> > +        fixes that.  */
> > +     andl    $(CHAR_PER_VEC * 4 - 1), %esi
> >       testl   %eax, %eax
> > -     jnz     L(first_vec_x0)
> > +     jnz     L(last_vec_x1_check)
> >
> > -     VPCMP   $0, VEC_SIZE(%rdi), %YMMZERO, %k0
> > -     kmovd   %k0, %eax
> > -     testl   %eax, %eax
> > -     jnz     L(first_vec_x1)
> > +     /* Check the end of data.  */
> > +     subl    $CHAR_PER_VEC, %esi
> > +     jb      L(max)
> >
> >       VPCMP   $0, (VEC_SIZE * 2)(%rdi), %YMMZERO, %k0
> >       kmovd   %k0, %eax
> > -     testl   %eax, %eax
> > -     jnz     L(first_vec_x2_check)
> > -     subl    $VEC_SIZE, %esi
> > -     jle     L(max)
> > +     tzcntl  %eax, %eax
> > +     /* Check the end of data.  */
> > +     cmpl    %eax, %esi
> > +     jb      L(max)
> >
> > -     VPCMP   $0, (VEC_SIZE * 3)(%rdi), %YMMZERO, %k0
> > -     kmovd   %k0, %eax
> > -     testl   %eax, %eax
> > -     jnz     L(first_vec_x3_check)
> > +     subq    %rdx, %rdi
> > +#  ifdef USE_AS_WCSLEN
> > +     /* NB: Divide bytes by 4 to get the wchar_t count.  */
> > +     sarq    $2, %rdi
> > +#  endif
> > +     leaq    (CHAR_PER_VEC * 2)(%rdi, %rax), %rax
> > +     ret
> > +L(max):
> >       movq    %r8, %rax
> > +     ret
> > +# endif
> > +
> > +     /* Placed here in strnlen so that the jcc L(last_4x_vec_or_less)
> > +        in the 4x VEC loop can use 2 byte encoding.  */
> > +     .p2align 4
> > +L(second_vec_return):
> > +     VPCMP   $0, %YMM3, %YMMZERO, %k0
> > +     /* Combine YMM3 matches (k0) with YMM4 matches (k1).  */
> > +# ifdef USE_AS_WCSLEN
> > +     kunpckbw        %k0, %k1, %k0
> > +     kmovd   %k0, %eax
> > +     tzcntl  %eax, %eax
> > +# else
> > +     kunpckdq        %k0, %k1, %k0
> > +     kmovq   %k0, %rax
> > +     tzcntq  %rax, %rax
> > +# endif
> > +     leaq    (CHAR_PER_VEC * 2)(%rdi, %rax), %rax
> > +     ret
> > +
> > +
> > +# ifdef USE_AS_STRNLEN
> > +L(last_vec_x1_check):
> > +     tzcntl  %eax, %eax
> > +     /* Check the end of data.  */
> > +     cmpl    %eax, %esi
> > +     jb      L(max)
> > +     subq    %rdx, %rdi
> >  #  ifdef USE_AS_WCSLEN
> > -     shrq    $2, %rax
> > +     /* NB: Divide bytes by 4 to get the wchar_t count.  */
> > +     sarq    $2, %rdi
> >  #  endif
> > +     leaq    (CHAR_PER_VEC)(%rdi, %rax), %rax
> >       ret
> >
> >       .p2align 4
> > -L(last_2x_vec):
> > -     addl    $(VEC_SIZE * 2), %esi
> > +L(last_4x_vec):
> > +     /* Test first 2x VEC normally.  */
> > +     testl   %eax, %eax
> > +     jnz     L(last_vec_x1)
> >
> > -     VPCMP   $0, (%rdi), %YMMZERO, %k0
> > +     VPCMP   $0, (VEC_SIZE * 2)(%rdi), %YMMZERO, %k0
> >       kmovd   %k0, %eax
> >       testl   %eax, %eax
> > -     jnz     L(first_vec_x0_check)
> > -     subl    $VEC_SIZE, %esi
> > -     jle     L(max)
> > +     jnz     L(last_vec_x2)
> >
> > -     VPCMP   $0, VEC_SIZE(%rdi), %YMMZERO, %k0
> > +     /* Normalize length.  */
> > +     andl    $(CHAR_PER_VEC * 4 - 1), %esi
> > +     VPCMP   $0, (VEC_SIZE * 3)(%rdi), %YMMZERO, %k0
> >       kmovd   %k0, %eax
> >       testl   %eax, %eax
> > -     jnz     L(first_vec_x1_check)
> > -     movq    %r8, %rax
> > -#  ifdef USE_AS_WCSLEN
> > -     shrq    $2, %rax
> > -#  endif
> > -     ret
> > +     jnz     L(last_vec_x3)
> >
> > -     .p2align 4
> > -L(first_vec_x0_check):
> > +     /* Check the end of data.  */
> > +     subl    $(CHAR_PER_VEC * 3), %esi
> > +     jb      L(max)
> > +
> > +     VPCMP   $0, (VEC_SIZE * 4)(%rdi), %YMMZERO, %k0
> > +     kmovd   %k0, %eax
> >       tzcntl  %eax, %eax
> > -#  ifdef USE_AS_WCSLEN
> > -     /* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> > -     sall    $2, %eax
> > -#  endif
> >       /* Check the end of data.  */
> > -     cmpq    %rax, %rsi
> > -     jbe     L(max)
> > -     addq    %rdi, %rax
> > -     subq    %rdx, %rax
> > +     cmpl    %eax, %esi
> > +     jb      L(max_end)
> > +
> > +     subq    %rdx, %rdi
> >  #  ifdef USE_AS_WCSLEN
> > -     shrq    $2, %rax
> > +     /* NB: Divide bytes by 4 to get the wchar_t count.  */
> > +     sarq    $2, %rdi
> >  #  endif
> > +     leaq    (CHAR_PER_VEC * 4)(%rdi, %rax), %rax
> >       ret
> >
> >       .p2align 4
> > -L(first_vec_x1_check):
> > +L(last_vec_x1):
> >       tzcntl  %eax, %eax
> > +     subq    %rdx, %rdi
> >  #  ifdef USE_AS_WCSLEN
> > -     /* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> > -     sall    $2, %eax
> > -#  endif
> > -     /* Check the end of data.  */
> > -     cmpq    %rax, %rsi
> > -     jbe     L(max)
> > -     addq    $VEC_SIZE, %rax
> > -     addq    %rdi, %rax
> > -     subq    %rdx, %rax
> > -#  ifdef USE_AS_WCSLEN
> > -     shrq    $2, %rax
> > +     /* NB: Divide bytes by 4 to get the wchar_t count.  */
> > +     sarq    $2, %rdi
> >  #  endif
> > +     leaq    (CHAR_PER_VEC)(%rdi, %rax), %rax
> >       ret
> >
> >       .p2align 4
> > -L(first_vec_x2_check):
> > +L(last_vec_x2):
> >       tzcntl  %eax, %eax
> > +     subq    %rdx, %rdi
> >  #  ifdef USE_AS_WCSLEN
> > -     /* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> > -     sall    $2, %eax
> > -#  endif
> > -     /* Check the end of data.  */
> > -     cmpq    %rax, %rsi
> > -     jbe     L(max)
> > -     addq    $(VEC_SIZE * 2), %rax
> > -     addq    %rdi, %rax
> > -     subq    %rdx, %rax
> > -#  ifdef USE_AS_WCSLEN
> > -     shrq    $2, %rax
> > +     /* NB: Divide bytes by 4 to get the wchar_t count.  */
> > +     sarq    $2, %rdi
> >  #  endif
> > +     leaq    (CHAR_PER_VEC * 2)(%rdi, %rax), %rax
> >       ret
> >
> >       .p2align 4
> > -L(first_vec_x3_check):
> > +L(last_vec_x3):
> >       tzcntl  %eax, %eax
> > -#  ifdef USE_AS_WCSLEN
> > -     /* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> > -     sall    $2, %eax
> > -#  endif
> > +     subl    $(CHAR_PER_VEC * 2), %esi
> >       /* Check the end of data.  */
> > -     cmpq    %rax, %rsi
> > -     jbe     L(max)
> > -     addq    $(VEC_SIZE * 3), %rax
> > -     addq    %rdi, %rax
> > -     subq    %rdx, %rax
> > +     cmpl    %eax, %esi
> > +     jb      L(max_end)
> > +     subq    %rdx, %rdi
> >  #  ifdef USE_AS_WCSLEN
> > -     shrq    $2, %rax
> > +     /* NB: Divide bytes by 4 to get the wchar_t count.  */
> > +     sarq    $2, %rdi
> >  #  endif
> > +     leaq    (CHAR_PER_VEC * 3)(%rdi, %rax), %rax
> >       ret
> > -
> > -     .p2align 4
> > -L(max):
> > +L(max_end):
> >       movq    %r8, %rax
> > -#  ifdef USE_AS_WCSLEN
> > -     shrq    $2, %rax
> > -#  endif
> > -     ret
> > -
> > -     .p2align 4
> > -L(zero):
> > -     xorl    %eax, %eax
> >       ret
> >  # endif
> >
> > +     /* Cold case for crossing page with first load.  */
> >       .p2align 4
> > -L(first_vec_x0):
> > -     tzcntl  %eax, %eax
> > -# ifdef USE_AS_WCSLEN
> > -     /* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> > -     sall    $2, %eax
> > -# endif
> > -     addq    %rdi, %rax
> > -     subq    %rdx, %rax
> > +L(cross_page_boundary):
> > +     movq    %rdi, %rdx
> > +     /* Align data to VEC_SIZE.  */
> > +     andq    $-VEC_SIZE, %rdi
> > +     VPCMP   $0, (%rdi), %YMMZERO, %k0
> > +     kmovd   %k0, %eax
> > +     /* Remove the leading bytes.  */
> >  # ifdef USE_AS_WCSLEN
> > -     shrq    $2, %rax
> > +     /* NB: Divide shift count by 4 since each bit in K0 represent 4
> > +        bytes.  */
> > +     movl    %edx, %ecx
> > +     shrl    $2, %ecx
> > +     andl    $(CHAR_PER_VEC - 1), %ecx
> >  # endif
> > -     ret
> > -
> > -     .p2align 4
> > -L(first_vec_x1):
> > +     /* SHIFT_REG is ecx for USE_AS_WCSLEN and edx otherwise.  */
> > +     sarxl   %SHIFT_REG, %eax, %eax
> > +     testl   %eax, %eax
> > +# ifndef USE_AS_STRNLEN
> > +     jz      L(cross_page_continue)
> >       tzcntl  %eax, %eax
> > -# ifdef USE_AS_WCSLEN
> > -     /* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> > -     sall    $2, %eax
> > -# endif
> > -     addq    $VEC_SIZE, %rax
> > -     addq    %rdi, %rax
> > -     subq    %rdx, %rax
> > -# ifdef USE_AS_WCSLEN
> > -     shrq    $2, %rax
> > -# endif
> >       ret
> > -
> > -     .p2align 4
> > -L(first_vec_x2):
> > -     tzcntl  %eax, %eax
> > -# ifdef USE_AS_WCSLEN
> > -     /* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> > -     sall    $2, %eax
> > -# endif
> > -     addq    $(VEC_SIZE * 2), %rax
> > -     addq    %rdi, %rax
> > -     subq    %rdx, %rax
> > -# ifdef USE_AS_WCSLEN
> > -     shrq    $2, %rax
> > -# endif
> > +# else
> > +     jnz     L(cross_page_less_vec)
> > +#  ifndef USE_AS_WCSLEN
> > +     movl    %edx, %ecx
> > +     andl    $(CHAR_PER_VEC - 1), %ecx
> > +#  endif
> > +     movl    $CHAR_PER_VEC, %eax
> > +     subl    %ecx, %eax
> > +     /* Check the end of data.  */
> > +     cmpq    %rax, %rsi
> > +     ja      L(cross_page_continue)
> > +     movl    %esi, %eax
> >       ret
> > -
> > -     .p2align 4
> > -L(4x_vec_end):
> > -     VPCMP   $0, %YMM1, %YMMZERO, %k0
> > -     kmovd   %k0, %eax
> > -     testl   %eax, %eax
> > -     jnz     L(first_vec_x0)
> > -     VPCMP   $0, %YMM2, %YMMZERO, %k1
> > -     kmovd   %k1, %eax
> > -     testl   %eax, %eax
> > -     jnz     L(first_vec_x1)
> > -     VPCMP   $0, %YMM3, %YMMZERO, %k2
> > -     kmovd   %k2, %eax
> > -     testl   %eax, %eax
> > -     jnz     L(first_vec_x2)
> > -     VPCMP   $0, %YMM4, %YMMZERO, %k3
> > -     kmovd   %k3, %eax
> > -L(first_vec_x3):
> > +L(cross_page_less_vec):
> >       tzcntl  %eax, %eax
> > -# ifdef USE_AS_WCSLEN
> > -     /* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
> > -     sall    $2, %eax
> > -# endif
> > -     addq    $(VEC_SIZE * 3), %rax
> > -     addq    %rdi, %rax
> > -     subq    %rdx, %rax
> > -# ifdef USE_AS_WCSLEN
> > -     shrq    $2, %rax
> > -# endif
> > +     /* Select min of length and position of first null.  */
> > +     cmpq    %rax, %rsi
> > +     cmovb   %esi, %eax
> >       ret
> > +# endif
> >
> >  END (STRLEN)
> >  #endif
> > --
> > 2.29.2
> >
diff mbox series

Patch

diff --git a/sysdeps/x86_64/multiarch/strlen-evex.S b/sysdeps/x86_64/multiarch/strlen-evex.S
index 0583819078..36b28198c8 100644
--- a/sysdeps/x86_64/multiarch/strlen-evex.S
+++ b/sysdeps/x86_64/multiarch/strlen-evex.S
@@ -29,11 +29,13 @@ 
 # ifdef USE_AS_WCSLEN
 #  define VPCMP		vpcmpd
 #  define VPMINU	vpminud
-#  define SHIFT_REG	r9d
+#  define SHIFT_REG ecx
+#  define CHAR_SIZE	4
 # else
 #  define VPCMP		vpcmpb
 #  define VPMINU	vpminub
-#  define SHIFT_REG	ecx
+#  define SHIFT_REG edx
+#  define CHAR_SIZE	1
 # endif
 
 # define XMMZERO	xmm16
@@ -46,132 +48,168 @@ 
 # define YMM6		ymm22
 
 # define VEC_SIZE 32
+# define PAGE_SIZE 4096
+# define LOG_PAGE_SIZE 12
+# define CHAR_PER_VEC (VEC_SIZE / CHAR_SIZE)
 
 	.section .text.evex,"ax",@progbits
 ENTRY (STRLEN)
 # ifdef USE_AS_STRNLEN
-	/* Check for zero length.  */
+	/* Check zero length.  */
 	test	%RSI_LP, %RSI_LP
 	jz	L(zero)
-#  ifdef USE_AS_WCSLEN
-	shl	$2, %RSI_LP
-#  elif defined __ILP32__
+#  ifdef __ILP32__
 	/* Clear the upper 32 bits.  */
 	movl	%esi, %esi
 #  endif
 	mov	%RSI_LP, %R8_LP
 # endif
-	movl	%edi, %ecx
-	movq	%rdi, %rdx
+	movl	%edi, %eax
 	vpxorq	%XMMZERO, %XMMZERO, %XMMZERO
-
+	/* Shift left eax to clear all bits not relevant to page cross
+	   check. This saves 2 bytes of code as opposed to using andl with
+	   PAGE_SIZE - 1. Then compare with PAGE_SIZE - VEC_SIZE shifted
+	   left by the same amount (an imm32 either way).  */
+	sall	$(32 - LOG_PAGE_SIZE), %eax
 	/* 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) << (32 - LOG_PAGE_SIZE)), %eax
+	ja	L(cross_page_boundary)
 
 	/* Check the first VEC_SIZE bytes.  Each bit in K0 represents a
 	   null byte.  */
 	VPCMP	$0, (%rdi), %YMMZERO, %k0
 	kmovd	%k0, %eax
-	testl	%eax, %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 < CHAR_PER_VEC handle special.  */
+	cmpq	$CHAR_PER_VEC, %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
+	ret
 # 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):
+	/* Set bit for max len so that tzcnt will return min of max len
+	   and position of first match.  */
+	btsq	%rsi, %rax
+	tzcntl	%eax, %eax
+	ret
 # endif
-	jmp	L(more_4x_vec)
 
 	.p2align 4
-L(cros_page_boundary):
-	andl	$(VEC_SIZE - 1), %ecx
-	andq	$-VEC_SIZE, %rdi
-
-# ifdef USE_AS_WCSLEN
-	/* NB: Divide shift count by 4 since each bit in K0 represent 4
-	   bytes.  */
-	movl	%ecx, %SHIFT_REG
-	sarl	$2, %SHIFT_REG
+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
+	/* Use ecx which was computed earlier to compute correct value.
+	 */
+	leal	-(CHAR_PER_VEC * 4 + 1)(%rcx, %rax), %eax
+# else
+	subl	%edx, %edi
+#  ifdef USE_AS_WCSLEN
+	/* NB: Divide bytes by 4 to get the wchar_t count.  */
+	sarl	$2, %edi
+#  endif
+	leal	CHAR_PER_VEC(%rdi, %rax), %eax
 # endif
-	VPCMP	$0, (%rdi), %YMMZERO, %k0
-	kmovd	%k0, %eax
+	ret
 
-	/* Remove the leading bytes.  */
-	sarxl	%SHIFT_REG, %eax, %eax
-	testl	%eax, %eax
-	jz	L(aligned_more)
+	.p2align 4
+L(first_vec_x2):
 	tzcntl	%eax, %eax
-# ifdef USE_AS_WCSLEN
-	/* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
-	sall	$2, %eax
-# endif
+	/* 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)
-# endif
-	addq	%rdi, %rax
-	addq	%rcx, %rax
-	subq	%rdx, %rax
-# ifdef USE_AS_WCSLEN
-	shrq	$2, %rax
+	/* Use ecx which was computed earlier to compute correct value.
+	 */
+	leal	-(CHAR_PER_VEC * 3 + 1)(%rcx, %rax), %eax
+# else
+	subl	%edx, %edi
+#  ifdef USE_AS_WCSLEN
+	/* NB: Divide bytes by 4 to get the wchar_t count.  */
+	sarl	$2, %edi
+#  endif
+	leal	(CHAR_PER_VEC * 2)(%rdi, %rax), %eax
 # endif
 	ret
 
 	.p2align 4
-L(aligned_more):
+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
-        /* "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.
+	 */
+	leal	-(CHAR_PER_VEC * 2 + 1)(%rcx, %rax), %eax
+# else
+	subl	%edx, %edi
+#  ifdef USE_AS_WCSLEN
+	/* NB: Divide bytes by 4 to get the wchar_t count.  */
+	sarl	$2, %edi
+#  endif
+	leal	(CHAR_PER_VEC * 3)(%rdi, %rax), %eax
 # endif
+	ret
 
-	addq	$VEC_SIZE, %rdi
-
+	.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.
+	 */
+	leal	-(CHAR_PER_VEC + 1)(%rcx, %rax), %eax
+# else
+	subl	%edx, %edi
+#  ifdef USE_AS_WCSLEN
+	/* NB: Divide bytes by 4 to get the wchar_t count.  */
+	sarl	$2, %edi
+#  endif
+	leal	(CHAR_PER_VEC * 4)(%rdi, %rax), %eax
 # endif
+	ret
 
-L(more_4x_vec):
+	.p2align 5
+L(aligned_more):
+	movq	%rdi, %rdx
+	/* Align data to VEC_SIZE.  */
+	andq	$-(VEC_SIZE), %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.  */
-	VPCMP	$0, (%rdi), %YMMZERO, %k0
-	kmovd	%k0, %eax
-	testl	%eax, %eax
-	jnz	L(first_vec_x0)
-
+# ifdef USE_AS_STRNLEN
+	/* + CHAR_SIZE because it simplies the logic in
+	   last_4x_vec_or_less.  */
+	leaq	(VEC_SIZE * 5 + CHAR_SIZE)(%rdi), %rcx
+	subq	%rdx, %rcx
+#  ifdef USE_AS_WCSLEN
+	/* NB: Divide bytes by 4 to get the wchar_t count.  */
+	sarl	$2, %ecx
+#  endif
+# endif
+	/* Load first VEC regardless.  */
 	VPCMP	$0, VEC_SIZE(%rdi), %YMMZERO, %k0
+# ifdef USE_AS_STRNLEN
+	/* Adjust length. If near end handle specially.  */
+	subq	%rcx, %rsi
+	jb	L(last_4x_vec_or_less)
+# endif
 	kmovd	%k0, %eax
 	testl	%eax, %eax
 	jnz	L(first_vec_x1)
 
 	VPCMP	$0, (VEC_SIZE * 2)(%rdi), %YMMZERO, %k0
 	kmovd	%k0, %eax
-	testl	%eax, %eax
+	test	%eax, %eax
 	jnz	L(first_vec_x2)
 
 	VPCMP	$0, (VEC_SIZE * 3)(%rdi), %YMMZERO, %k0
@@ -179,258 +217,276 @@  L(more_4x_vec):
 	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
+	VPCMP	$0, (VEC_SIZE * 4)(%rdi), %YMMZERO, %k0
+	kmovd	%k0, %eax
+	testl	%eax, %eax
+	jnz	L(first_vec_x4)
 
+	addq	$VEC_SIZE, %rdi
 # ifdef USE_AS_STRNLEN
-	/* Adjust length.  */
+	/* Check if at last VEC_SIZE * 4 length.  */
+	cmpq	$(CHAR_PER_VEC * 4 - 1), %rsi
+	jbe	L(last_4x_vec_or_less_load)
+	movl	%edi, %ecx
+	andl	$(VEC_SIZE * 4 - 1), %ecx
+#  ifdef USE_AS_WCSLEN
+	/* NB: Divide bytes by 4 to get the wchar_t count.  */
+	sarl	$2, %ecx
+#  endif
+	/* Readjust length.  */
 	addq	%rcx, %rsi
 # endif
+	/* Align data to VEC_SIZE * 4.  */
+	andq	$-(VEC_SIZE * 4), %rdi
 
+	/* Compare 4 * VEC at a time forward.  */
 	.p2align 4
 L(loop_4x_vec):
-	/* Compare 4 * VEC at a time forward.  */
-	VMOVA	(%rdi), %YMM1
-	VMOVA	VEC_SIZE(%rdi), %YMM2
-	VMOVA	(VEC_SIZE * 2)(%rdi), %YMM3
-	VMOVA	(VEC_SIZE * 3)(%rdi), %YMM4
-
-	VPMINU	%YMM1, %YMM2, %YMM5
-	VPMINU	%YMM3, %YMM4, %YMM6
+	/* Load first VEC regardless.  */
+	VMOVA	(VEC_SIZE * 4)(%rdi), %YMM1
+# ifdef USE_AS_STRNLEN
+	/* Break if at end of length.  */
+	subq	$(CHAR_PER_VEC * 4), %rsi
+	jb	L(last_4x_vec_or_less_cmpeq)
+# endif
+	/* Save some code size by microfusing VPMINU with the load. Since
+	   the matches in ymm2/ymm4 can only be returned if there where no
+	   matches in ymm1/ymm3 respectively there is no issue with overlap.
+	 */
+	VPMINU	(VEC_SIZE * 5)(%rdi), %YMM1, %YMM2
+	VMOVA	(VEC_SIZE * 6)(%rdi), %YMM3
+	VPMINU	(VEC_SIZE * 7)(%rdi), %YMM3, %YMM4
+
+	VPCMP	$0, %YMM2, %YMMZERO, %k0
+	VPCMP	$0, %YMM4, %YMMZERO, %k1
+	subq	$-(VEC_SIZE * 4), %rdi
+	kortestd	%k0, %k1
+	jz	L(loop_4x_vec)
+
+	/* Check if end was in first half.  */
+	kmovd	%k0, %eax
+	subq	%rdx, %rdi
+# ifdef USE_AS_WCSLEN
+	shrq	$2, %rdi
+# endif
+	testl	%eax, %eax
+	jz	L(second_vec_return)
 
-	VPMINU	%YMM5, %YMM6, %YMM5
-	VPCMP	$0, %YMM5, %YMMZERO, %k0
-	ktestd	%k0, %k0
-	jnz	L(4x_vec_end)
+	VPCMP	$0, %YMM1, %YMMZERO, %k2
+	kmovd	%k2, %edx
+	/* Combine VEC1 matches (edx) with VEC2 matches (eax).  */
+# ifdef USE_AS_WCSLEN
+	sall	$CHAR_PER_VEC, %eax
+	orl	%edx, %eax
+	tzcntl	%eax, %eax
+# else
+	salq	$CHAR_PER_VEC, %rax
+	orq	%rdx, %rax
+	tzcntq	%rax, %rax
+# endif
+	addq	%rdi, %rax
+	ret
 
-	addq	$(VEC_SIZE * 4), %rdi
 
-# ifndef USE_AS_STRNLEN
-	jmp	L(loop_4x_vec)
-# else
-	subq	$(VEC_SIZE * 4), %rsi
-	ja	L(loop_4x_vec)
+# ifdef USE_AS_STRNLEN
 
+L(last_4x_vec_or_less_load):
+	/* Depending on entry adjust rdi / prepare first VEC in YMM1.  */
+	VMOVA	(VEC_SIZE * 4)(%rdi), %YMM1
+L(last_4x_vec_or_less_cmpeq):
+	VPCMP	$0, %YMM1, %YMMZERO, %k0
+	addq	$(VEC_SIZE * 3), %rdi
 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)
-
-	VPCMP	$0, (%rdi), %YMMZERO, %k0
 	kmovd	%k0, %eax
+	/* If remaining length > VEC_SIZE * 2. This works if esi is off by
+	   VEC_SIZE * 4.  */
+	testl	$(CHAR_PER_VEC * 2), %esi
+	jnz	L(last_4x_vec)
+
+	/* length may have been negative or positive by an offset of
+	   CHAR_PER_VEC * 4 depending on where this was called from. This
+	   fixes that.  */
+	andl	$(CHAR_PER_VEC * 4 - 1), %esi
 	testl	%eax, %eax
-	jnz	L(first_vec_x0)
+	jnz	L(last_vec_x1_check)
 
-	VPCMP	$0, VEC_SIZE(%rdi), %YMMZERO, %k0
-	kmovd	%k0, %eax
-	testl	%eax, %eax
-	jnz	L(first_vec_x1)
+	/* Check the end of data.  */
+	subl	$CHAR_PER_VEC, %esi
+	jb	L(max)
 
 	VPCMP	$0, (VEC_SIZE * 2)(%rdi), %YMMZERO, %k0
 	kmovd	%k0, %eax
-	testl	%eax, %eax
-	jnz	L(first_vec_x2_check)
-	subl	$VEC_SIZE, %esi
-	jle	L(max)
+	tzcntl	%eax, %eax
+	/* Check the end of data.  */
+	cmpl	%eax, %esi
+	jb	L(max)
 
-	VPCMP	$0, (VEC_SIZE * 3)(%rdi), %YMMZERO, %k0
-	kmovd	%k0, %eax
-	testl	%eax, %eax
-	jnz	L(first_vec_x3_check)
+	subq	%rdx, %rdi
+#  ifdef USE_AS_WCSLEN
+	/* NB: Divide bytes by 4 to get the wchar_t count.  */
+	sarq	$2, %rdi
+#  endif
+	leaq	(CHAR_PER_VEC * 2)(%rdi, %rax), %rax
+	ret
+L(max):
 	movq	%r8, %rax
+	ret
+# endif
+
+	/* Placed here in strnlen so that the jcc L(last_4x_vec_or_less)
+	   in the 4x VEC loop can use 2 byte encoding.  */
+	.p2align 4
+L(second_vec_return):
+	VPCMP	$0, %YMM3, %YMMZERO, %k0
+	/* Combine YMM3 matches (k0) with YMM4 matches (k1).  */
+# ifdef USE_AS_WCSLEN
+	kunpckbw	%k0, %k1, %k0
+	kmovd	%k0, %eax
+	tzcntl	%eax, %eax
+# else
+	kunpckdq	%k0, %k1, %k0
+	kmovq	%k0, %rax
+	tzcntq	%rax, %rax
+# endif
+	leaq	(CHAR_PER_VEC * 2)(%rdi, %rax), %rax
+	ret
+
+
+# ifdef USE_AS_STRNLEN
+L(last_vec_x1_check):
+	tzcntl	%eax, %eax
+	/* Check the end of data.  */
+	cmpl	%eax, %esi
+	jb	L(max)
+	subq	%rdx, %rdi
 #  ifdef USE_AS_WCSLEN
-	shrq	$2, %rax
+	/* NB: Divide bytes by 4 to get the wchar_t count.  */
+	sarq	$2, %rdi
 #  endif
+	leaq	(CHAR_PER_VEC)(%rdi, %rax), %rax
 	ret
 
 	.p2align 4
-L(last_2x_vec):
-	addl	$(VEC_SIZE * 2), %esi
+L(last_4x_vec):
+	/* Test first 2x VEC normally.  */
+	testl	%eax, %eax
+	jnz	L(last_vec_x1)
 
-	VPCMP	$0, (%rdi), %YMMZERO, %k0
+	VPCMP	$0, (VEC_SIZE * 2)(%rdi), %YMMZERO, %k0
 	kmovd	%k0, %eax
 	testl	%eax, %eax
-	jnz	L(first_vec_x0_check)
-	subl	$VEC_SIZE, %esi
-	jle	L(max)
+	jnz	L(last_vec_x2)
 
-	VPCMP	$0, VEC_SIZE(%rdi), %YMMZERO, %k0
+	/* Normalize length.  */
+	andl	$(CHAR_PER_VEC * 4 - 1), %esi
+	VPCMP	$0, (VEC_SIZE * 3)(%rdi), %YMMZERO, %k0
 	kmovd	%k0, %eax
 	testl	%eax, %eax
-	jnz	L(first_vec_x1_check)
-	movq	%r8, %rax
-#  ifdef USE_AS_WCSLEN
-	shrq	$2, %rax
-#  endif
-	ret
+	jnz	L(last_vec_x3)
 
-	.p2align 4
-L(first_vec_x0_check):
+	/* Check the end of data.  */
+	subl	$(CHAR_PER_VEC * 3), %esi
+	jb	L(max)
+
+	VPCMP	$0, (VEC_SIZE * 4)(%rdi), %YMMZERO, %k0
+	kmovd	%k0, %eax
 	tzcntl	%eax, %eax
-#  ifdef USE_AS_WCSLEN
-	/* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
-	sall	$2, %eax
-#  endif
 	/* Check the end of data.  */
-	cmpq	%rax, %rsi
-	jbe	L(max)
-	addq	%rdi, %rax
-	subq	%rdx, %rax
+	cmpl	%eax, %esi
+	jb	L(max_end)
+
+	subq	%rdx, %rdi
 #  ifdef USE_AS_WCSLEN
-	shrq	$2, %rax
+	/* NB: Divide bytes by 4 to get the wchar_t count.  */
+	sarq	$2, %rdi
 #  endif
+	leaq	(CHAR_PER_VEC * 4)(%rdi, %rax), %rax
 	ret
 
 	.p2align 4
-L(first_vec_x1_check):
+L(last_vec_x1):
 	tzcntl	%eax, %eax
+	subq	%rdx, %rdi
 #  ifdef USE_AS_WCSLEN
-	/* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
-	sall	$2, %eax
-#  endif
-	/* Check the end of data.  */
-	cmpq	%rax, %rsi
-	jbe	L(max)
-	addq	$VEC_SIZE, %rax
-	addq	%rdi, %rax
-	subq	%rdx, %rax
-#  ifdef USE_AS_WCSLEN
-	shrq	$2, %rax
+	/* NB: Divide bytes by 4 to get the wchar_t count.  */
+	sarq	$2, %rdi
 #  endif
+	leaq	(CHAR_PER_VEC)(%rdi, %rax), %rax
 	ret
 
 	.p2align 4
-L(first_vec_x2_check):
+L(last_vec_x2):
 	tzcntl	%eax, %eax
+	subq	%rdx, %rdi
 #  ifdef USE_AS_WCSLEN
-	/* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
-	sall	$2, %eax
-#  endif
-	/* Check the end of data.  */
-	cmpq	%rax, %rsi
-	jbe	L(max)
-	addq	$(VEC_SIZE * 2), %rax
-	addq	%rdi, %rax
-	subq	%rdx, %rax
-#  ifdef USE_AS_WCSLEN
-	shrq	$2, %rax
+	/* NB: Divide bytes by 4 to get the wchar_t count.  */
+	sarq	$2, %rdi
 #  endif
+	leaq	(CHAR_PER_VEC * 2)(%rdi, %rax), %rax
 	ret
 
 	.p2align 4
-L(first_vec_x3_check):
+L(last_vec_x3):
 	tzcntl	%eax, %eax
-#  ifdef USE_AS_WCSLEN
-	/* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
-	sall	$2, %eax
-#  endif
+	subl	$(CHAR_PER_VEC * 2), %esi
 	/* Check the end of data.  */
-	cmpq	%rax, %rsi
-	jbe	L(max)
-	addq	$(VEC_SIZE * 3), %rax
-	addq	%rdi, %rax
-	subq	%rdx, %rax
+	cmpl	%eax, %esi
+	jb	L(max_end)
+	subq	%rdx, %rdi
 #  ifdef USE_AS_WCSLEN
-	shrq	$2, %rax
+	/* NB: Divide bytes by 4 to get the wchar_t count.  */
+	sarq	$2, %rdi
 #  endif
+	leaq	(CHAR_PER_VEC * 3)(%rdi, %rax), %rax
 	ret
-
-	.p2align 4
-L(max):
+L(max_end):
 	movq	%r8, %rax
-#  ifdef USE_AS_WCSLEN
-	shrq	$2, %rax
-#  endif
-	ret
-
-	.p2align 4
-L(zero):
-	xorl	%eax, %eax
 	ret
 # endif
 
+	/* Cold case for crossing page with first load.	 */
 	.p2align 4
-L(first_vec_x0):
-	tzcntl	%eax, %eax
-# ifdef USE_AS_WCSLEN
-	/* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
-	sall	$2, %eax
-# endif
-	addq	%rdi, %rax
-	subq	%rdx, %rax
+L(cross_page_boundary):
+	movq	%rdi, %rdx
+	/* Align data to VEC_SIZE.  */
+	andq	$-VEC_SIZE, %rdi
+	VPCMP	$0, (%rdi), %YMMZERO, %k0
+	kmovd	%k0, %eax
+	/* Remove the leading bytes.  */
 # ifdef USE_AS_WCSLEN
-	shrq	$2, %rax
+	/* NB: Divide shift count by 4 since each bit in K0 represent 4
+	   bytes.  */
+	movl	%edx, %ecx
+	shrl	$2, %ecx
+	andl	$(CHAR_PER_VEC - 1), %ecx
 # endif
-	ret
-
-	.p2align 4
-L(first_vec_x1):
+	/* SHIFT_REG is ecx for USE_AS_WCSLEN and edx otherwise.  */
+	sarxl	%SHIFT_REG, %eax, %eax
+	testl	%eax, %eax
+# ifndef USE_AS_STRNLEN
+	jz	L(cross_page_continue)
 	tzcntl	%eax, %eax
-# ifdef USE_AS_WCSLEN
-	/* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
-	sall	$2, %eax
-# endif
-	addq	$VEC_SIZE, %rax
-	addq	%rdi, %rax
-	subq	%rdx, %rax
-# ifdef USE_AS_WCSLEN
-	shrq	$2, %rax
-# endif
 	ret
-
-	.p2align 4
-L(first_vec_x2):
-	tzcntl	%eax, %eax
-# ifdef USE_AS_WCSLEN
-	/* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
-	sall	$2, %eax
-# endif
-	addq	$(VEC_SIZE * 2), %rax
-	addq	%rdi, %rax
-	subq	%rdx, %rax
-# ifdef USE_AS_WCSLEN
-	shrq	$2, %rax
-# endif
+# else
+	jnz	L(cross_page_less_vec)
+#  ifndef USE_AS_WCSLEN
+	movl	%edx, %ecx
+	andl	$(CHAR_PER_VEC - 1), %ecx
+#  endif
+	movl	$CHAR_PER_VEC, %eax
+	subl	%ecx, %eax
+	/* Check the end of data.  */
+	cmpq	%rax, %rsi
+	ja	L(cross_page_continue)
+	movl	%esi, %eax
 	ret
-
-	.p2align 4
-L(4x_vec_end):
-	VPCMP	$0, %YMM1, %YMMZERO, %k0
-	kmovd	%k0, %eax
-	testl	%eax, %eax
-	jnz	L(first_vec_x0)
-	VPCMP	$0, %YMM2, %YMMZERO, %k1
-	kmovd	%k1, %eax
-	testl	%eax, %eax
-	jnz	L(first_vec_x1)
-	VPCMP	$0, %YMM3, %YMMZERO, %k2
-	kmovd	%k2, %eax
-	testl	%eax, %eax
-	jnz	L(first_vec_x2)
-	VPCMP	$0, %YMM4, %YMMZERO, %k3
-	kmovd	%k3, %eax
-L(first_vec_x3):
+L(cross_page_less_vec):
 	tzcntl	%eax, %eax
-# ifdef USE_AS_WCSLEN
-	/* NB: Multiply wchar_t count by 4 to get the number of bytes.  */
-	sall	$2, %eax
-# endif
-	addq	$(VEC_SIZE * 3), %rax
-	addq	%rdi, %rax
-	subq	%rdx, %rax
-# ifdef USE_AS_WCSLEN
-	shrq	$2, %rax
-# endif
+	/* Select min of length and position of first null.  */
+	cmpq	%rax, %rsi
+	cmovb	%esi, %eax
 	ret
+# endif
 
 END (STRLEN)
 #endif