From 417f10b43cd3a0bc5c67b0b5151e92b722bdd8d7 Mon Sep 17 00:00:00 2001

From: Noah Goldstein <goldstein.w.n@gmail.com>

Date: Mon, 19 Apr 2021 19:36:06 -0400

Subject: [PATCH] x86: Optimize strlen-evex.S

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>

(cherry picked from commit 4ba65586847751372520a36757c17f114588794e)

---

 sysdeps/x86_64/multiarch/strlen-evex.S | 581 ++++++++++++++-----------

 1 file changed, 317 insertions(+), 264 deletions(-)

diff --git a/sysdeps/x86_64/multiarch/strlen-evex.S b/sysdeps/x86_64/multiarch/strlen-evex.S

index 05838190..4bf6874b 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 +48,165 @@

 # define YMM6		ymm22

 # define VEC_SIZE 32

+# define PAGE_SIZE 4096

+# 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

-

+	/* Clear high bits from edi. Only keeping bits relevant to page

+	   cross check.  */

+	andl	$(PAGE_SIZE - 1), %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), %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 +214,276 @@ 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)