From f97e72cd3b822c04bfdda110dcf252b19afd2bcd Mon Sep 17 00:00:00 2001

From: "H.J. Lu" <hjl.tools@gmail.com>

Date: Wed, 2 Mar 2022 14:29:44 -0800

Subject: [PATCH] x86: Optimize strlen-avx2.S

No bug. This commit optimizes strlen-avx2.S. The optimizations are

mostly small things but they add up to roughly 10-30% performance

improvement for strlen. The results for strnlen are bit more

ambiguous. test-strlen, test-strnlen, test-wcslen, and test-wcsnlen

are all passing.

Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>

(cherry picked from commit aaa23c35071537e2dcf5807e956802ed215210aa)

---

 sysdeps/x86_64/multiarch/ifunc-impl-list.c |  16 +-

 sysdeps/x86_64/multiarch/strlen-avx2.S     | 532 +++++++++++++--------

 2 files changed, 334 insertions(+), 214 deletions(-)

diff --git a/sysdeps/x86_64/multiarch/ifunc-impl-list.c b/sysdeps/x86_64/multiarch/ifunc-impl-list.c

index cbfc1a5d..f1a6460a 100644

--- a/sysdeps/x86_64/multiarch/ifunc-impl-list.c

+++ b/sysdeps/x86_64/multiarch/ifunc-impl-list.c

@@ -285,10 +285,12 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,

   /* Support sysdeps/x86_64/multiarch/strlen.c.  */

   IFUNC_IMPL (i, name, strlen,

 	      IFUNC_IMPL_ADD (array, i, strlen,

-			      CPU_FEATURE_USABLE (AVX2),

+			      (CPU_FEATURE_USABLE (AVX2)

+			       && CPU_FEATURE_USABLE (BMI2)),

 			      __strlen_avx2)

 	      IFUNC_IMPL_ADD (array, i, strlen,

 			      (CPU_FEATURE_USABLE (AVX2)

+			       && CPU_FEATURE_USABLE (BMI2)

 			       && CPU_FEATURE_USABLE (RTM)),

 			      __strlen_avx2_rtm)

 	      IFUNC_IMPL_ADD (array, i, strlen,

@@ -301,10 +303,12 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,

   /* Support sysdeps/x86_64/multiarch/strnlen.c.  */

   IFUNC_IMPL (i, name, strnlen,

 	      IFUNC_IMPL_ADD (array, i, strnlen,

-			      CPU_FEATURE_USABLE (AVX2),

+			      (CPU_FEATURE_USABLE (AVX2)

+			       && CPU_FEATURE_USABLE (BMI2)),

 			      __strnlen_avx2)

 	      IFUNC_IMPL_ADD (array, i, strnlen,

 			      (CPU_FEATURE_USABLE (AVX2)

+			       && CPU_FEATURE_USABLE (BMI2)

 			       && CPU_FEATURE_USABLE (RTM)),

 			      __strnlen_avx2_rtm)

 	      IFUNC_IMPL_ADD (array, i, strnlen,

@@ -640,10 +644,12 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,

   /* Support sysdeps/x86_64/multiarch/wcslen.c.  */

   IFUNC_IMPL (i, name, wcslen,

 	      IFUNC_IMPL_ADD (array, i, wcslen,

-			      CPU_FEATURE_USABLE (AVX2),

+			      (CPU_FEATURE_USABLE (AVX2)

+			       && CPU_FEATURE_USABLE (BMI2)),

 			      __wcslen_avx2)

 	      IFUNC_IMPL_ADD (array, i, wcslen,

 			      (CPU_FEATURE_USABLE (AVX2)

+			       && CPU_FEATURE_USABLE (BMI2)

 			       && CPU_FEATURE_USABLE (RTM)),

 			      __wcslen_avx2_rtm)

 	      IFUNC_IMPL_ADD (array, i, wcslen,

@@ -656,10 +662,12 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,

   /* Support sysdeps/x86_64/multiarch/wcsnlen.c.  */

   IFUNC_IMPL (i, name, wcsnlen,

 	      IFUNC_IMPL_ADD (array, i, wcsnlen,

-			      CPU_FEATURE_USABLE (AVX2),

+			      (CPU_FEATURE_USABLE (AVX2)

+			       && CPU_FEATURE_USABLE (BMI2)),

 			      __wcsnlen_avx2)

 	      IFUNC_IMPL_ADD (array, i, wcsnlen,

 			      (CPU_FEATURE_USABLE (AVX2)

+			       && CPU_FEATURE_USABLE (BMI2)

 			       && CPU_FEATURE_USABLE (RTM)),

 			      __wcsnlen_avx2_rtm)

 	      IFUNC_IMPL_ADD (array, i, wcsnlen,

diff --git a/sysdeps/x86_64/multiarch/strlen-avx2.S b/sysdeps/x86_64/multiarch/strlen-avx2.S

index 82826e10..be8a5db5 100644

--- a/sysdeps/x86_64/multiarch/strlen-avx2.S

+++ b/sysdeps/x86_64/multiarch/strlen-avx2.S

@@ -27,9 +27,11 @@

 # ifdef USE_AS_WCSLEN

 #  define VPCMPEQ	vpcmpeqd

 #  define VPMINU	vpminud

+#  define CHAR_SIZE	4

 # else

 #  define VPCMPEQ	vpcmpeqb

 #  define VPMINU	vpminub

+#  define CHAR_SIZE	1

 # endif

 # ifndef VZEROUPPER

@@ -41,349 +43,459 @@

 # endif

 # define VEC_SIZE 32

+# define PAGE_SIZE 4096

 	.section SECTION(.text),"ax",@progbits

 ENTRY (STRLEN)

 # ifdef USE_AS_STRNLEN

-	/* Check for zero length.  */

+	/* Check zero length.  */

 	test	%RSI_LP, %RSI_LP

 	jz	L(zero)

+	/* Store max len in R8_LP before adjusting if using WCSLEN.  */

+	mov	%RSI_LP, %R8_LP

 #  ifdef USE_AS_WCSLEN

 	shl	$2, %RSI_LP

 #  elif defined __ILP32__

 	/* Clear the upper 32 bits.  */

 	movl	%esi, %esi

 #  endif

-	mov	%RSI_LP, %R8_LP

 # endif

-	movl	%edi, %ecx

+	movl	%edi, %eax

 	movq	%rdi, %rdx

 	vpxor	%xmm0, %xmm0, %xmm0

-

+	/* 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.  */

-	VPCMPEQ (%rdi), %ymm0, %ymm1

-	vpmovmskb %ymm1, %eax

-	testl	%eax, %eax

-

+	VPCMPEQ	(%rdi), %ymm0, %ymm1

+	vpmovmskb	%ymm1, %eax

 # ifdef USE_AS_STRNLEN

-	jnz	L(first_vec_x0_check)

-	/* Adjust length and check the end of data.  */

-	subq	$VEC_SIZE, %rsi

-	jbe	L(max)

-# else

-	jnz	L(first_vec_x0)

+	/* If length < VEC_SIZE handle special.  */

+	cmpq	$VEC_SIZE, %rsi

+	jbe	L(first_vec_x0)

 # endif

-

-	/* Align data for aligned loads in the loop.  */

-	addq	$VEC_SIZE, %rdi

-	andl	$(VEC_SIZE - 1), %ecx

-	andq	$-VEC_SIZE, %rdi

+	/* If empty continue to aligned_more. Otherwise return bit

+	   position of first match.  */

+	testl	%eax, %eax

+	jz	L(aligned_more)

+	tzcntl	%eax, %eax

+# ifdef USE_AS_WCSLEN

+	shrl	$2, %eax

+# endif

+	VZEROUPPER_RETURN

 # ifdef USE_AS_STRNLEN

-	/* Adjust length.  */

-	addq	%rcx, %rsi

+L(zero):

+	xorl	%eax, %eax

+	ret

-	subq	$(VEC_SIZE * 4), %rsi

-	jbe	L(last_4x_vec_or_less)

+	.p2align 4

+L(first_vec_x0):

+	/* 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

+#  ifdef USE_AS_WCSLEN

+	shrl	$2, %eax

+#  endif

+	VZEROUPPER_RETURN

 # endif

-	jmp	L(more_4x_vec)

 	.p2align 4

-L(cros_page_boundary):

-	andl	$(VEC_SIZE - 1), %ecx

-	andq	$-VEC_SIZE, %rdi

-	VPCMPEQ (%rdi), %ymm0, %ymm1

-	vpmovmskb %ymm1, %eax

-	/* Remove the leading bytes.  */

-	sarl	%cl, %eax

-	testl	%eax, %eax

-	jz	L(aligned_more)

+L(first_vec_x1):

 	tzcntl	%eax, %eax

+	/* Safe to use 32 bit instructions as these are only called for

+	   size = [1, 159].  */

 # ifdef USE_AS_STRNLEN

-	/* Check the end of data.  */

-	cmpq	%rax, %rsi

-	jbe	L(max)

+	/* Use ecx which was computed earlier to compute correct value.

+	 */

+	subl	$(VEC_SIZE * 4 + 1), %ecx

+	addl	%ecx, %eax

+# else

+	subl	%edx, %edi

+	incl	%edi

+	addl	%edi, %eax

 # endif

-	addq	%rdi, %rax

-	addq	%rcx, %rax

-	subq	%rdx, %rax

 # ifdef USE_AS_WCSLEN

-	shrq	$2, %rax

+	shrl	$2, %eax

 # endif

-L(return_vzeroupper):

-	ZERO_UPPER_VEC_REGISTERS_RETURN

+	VZEROUPPER_RETURN

 	.p2align 4

-L(aligned_more):

+L(first_vec_x2):

+	tzcntl	%eax, %eax

+	/* Safe to use 32 bit instructions as these are only called for

+	   size = [1, 159].  */

 # ifdef USE_AS_STRNLEN

-        /* "rcx" is less than VEC_SIZE.  Calculate "rdx + rcx - VEC_SIZE"

-	    with "rdx - (VEC_SIZE - rcx)" instead of "(rdx + rcx) - VEC_SIZE"

-	    to void possible addition overflow.  */

-	negq	%rcx

-	addq	$VEC_SIZE, %rcx

-

-	/* Check the end of data.  */

-	subq	%rcx, %rsi

-	jbe	L(max)

+	/* Use ecx which was computed earlier to compute correct value.

+	 */

+	subl	$(VEC_SIZE * 3 + 1), %ecx

+	addl	%ecx, %eax

+# else

+	subl	%edx, %edi

+	addl	$(VEC_SIZE + 1), %edi

+	addl	%edi, %eax

 # endif

+# ifdef USE_AS_WCSLEN

+	shrl	$2, %eax

+# endif

+	VZEROUPPER_RETURN

-	addq	$VEC_SIZE, %rdi

+	.p2align 4

+L(first_vec_x3):

+	tzcntl	%eax, %eax

+	/* Safe to use 32 bit instructions as these are only called for

+	   size = [1, 159].  */

+# ifdef USE_AS_STRNLEN

+	/* Use ecx which was computed earlier to compute correct value.

+	 */

+	subl	$(VEC_SIZE * 2 + 1), %ecx

+	addl	%ecx, %eax

+# else

+	subl	%edx, %edi

+	addl	$(VEC_SIZE * 2 + 1), %edi

+	addl	%edi, %eax

+# endif

+# ifdef USE_AS_WCSLEN

+	shrl	$2, %eax

+# endif

+	VZEROUPPER_RETURN

+	.p2align 4

+L(first_vec_x4):

+	tzcntl	%eax, %eax

+	/* Safe to use 32 bit instructions as these are only called for

+	   size = [1, 159].  */

 # ifdef USE_AS_STRNLEN

-	subq	$(VEC_SIZE * 4), %rsi

-	jbe	L(last_4x_vec_or_less)

+	/* Use ecx which was computed earlier to compute correct value.

+	 */

+	subl	$(VEC_SIZE + 1), %ecx

+	addl	%ecx, %eax

+# else

+	subl	%edx, %edi

+	addl	$(VEC_SIZE * 3 + 1), %edi

+	addl	%edi, %eax

 # endif

+# ifdef USE_AS_WCSLEN

+	shrl	$2, %eax

+# endif

+	VZEROUPPER_RETURN

-L(more_4x_vec):

+	.p2align 5

+L(aligned_more):

+	/* Align data to VEC_SIZE - 1. This is the same number of

+	   instructions as using andq with -VEC_SIZE but saves 4 bytes of

+	   code on the x4 check.  */

+	orq	$(VEC_SIZE - 1), %rdi

+L(cross_page_continue):

 	/* Check the first 4 * VEC_SIZE.  Only one VEC_SIZE at a time

 	   since data is only aligned to VEC_SIZE.  */

-	VPCMPEQ (%rdi), %ymm0, %ymm1

-	vpmovmskb %ymm1, %eax

-	testl	%eax, %eax

-	jnz	L(first_vec_x0)

-

-	VPCMPEQ VEC_SIZE(%rdi), %ymm0, %ymm1

-	vpmovmskb %ymm1, %eax

+# ifdef USE_AS_STRNLEN

+	/* + 1 because rdi is aligned to VEC_SIZE - 1. + CHAR_SIZE because

+	   it simplies the logic in last_4x_vec_or_less.  */

+	leaq	(VEC_SIZE * 4 + CHAR_SIZE + 1)(%rdi), %rcx

+	subq	%rdx, %rcx

+# endif

+	/* Load first VEC regardless.  */

+	VPCMPEQ	1(%rdi), %ymm0, %ymm1

+# ifdef USE_AS_STRNLEN

+	/* Adjust length. If near end handle specially.  */

+	subq	%rcx, %rsi

+	jb	L(last_4x_vec_or_less)

+# endif

+	vpmovmskb	%ymm1, %eax

 	testl	%eax, %eax

 	jnz	L(first_vec_x1)

-	VPCMPEQ (VEC_SIZE * 2)(%rdi), %ymm0, %ymm1

-	vpmovmskb %ymm1, %eax

+	VPCMPEQ	(VEC_SIZE + 1)(%rdi), %ymm0, %ymm1

+	vpmovmskb	%ymm1, %eax

 	testl	%eax, %eax

 	jnz	L(first_vec_x2)

-	VPCMPEQ (VEC_SIZE * 3)(%rdi), %ymm0, %ymm1

-	vpmovmskb %ymm1, %eax

+	VPCMPEQ	(VEC_SIZE * 2 + 1)(%rdi), %ymm0, %ymm1

+	vpmovmskb	%ymm1, %eax

 	testl	%eax, %eax

 	jnz	L(first_vec_x3)

-	addq	$(VEC_SIZE * 4), %rdi

-

-# ifdef USE_AS_STRNLEN

-	subq	$(VEC_SIZE * 4), %rsi

-	jbe	L(last_4x_vec_or_less)

-# endif

-

-	/* Align data to 4 * VEC_SIZE.  */

-	movq	%rdi, %rcx

-	andl	$(4 * VEC_SIZE - 1), %ecx

-	andq	$-(4 * VEC_SIZE), %rdi

+	VPCMPEQ	(VEC_SIZE * 3 + 1)(%rdi), %ymm0, %ymm1

+	vpmovmskb	%ymm1, %eax

+	testl	%eax, %eax

+	jnz	L(first_vec_x4)

+	/* Align data to VEC_SIZE * 4 - 1.  */

 # ifdef USE_AS_STRNLEN

-	/* Adjust length.  */

+	/* Before adjusting length check if at last VEC_SIZE * 4.  */

+	cmpq	$(VEC_SIZE * 4 - 1), %rsi

+	jbe	L(last_4x_vec_or_less_load)

+	incq	%rdi

+	movl	%edi, %ecx

+	orq	$(VEC_SIZE * 4 - 1), %rdi

+	andl	$(VEC_SIZE * 4 - 1), %ecx

+	/* Readjust length.  */

 	addq	%rcx, %rsi

+# else

+	incq	%rdi

+	orq	$(VEC_SIZE * 4 - 1), %rdi

 # endif

-

+	/* Compare 4 * VEC at a time forward.  */

 	.p2align 4

 L(loop_4x_vec):

-	/* Compare 4 * VEC at a time forward.  */

-	vmovdqa (%rdi), %ymm1

-	vmovdqa	VEC_SIZE(%rdi), %ymm2

-	vmovdqa	(VEC_SIZE * 2)(%rdi), %ymm3

-	vmovdqa	(VEC_SIZE * 3)(%rdi), %ymm4

-	VPMINU	%ymm1, %ymm2, %ymm5

-	VPMINU	%ymm3, %ymm4, %ymm6

-	VPMINU	%ymm5, %ymm6, %ymm5

-

-	VPCMPEQ	%ymm5, %ymm0, %ymm5

-	vpmovmskb %ymm5, %eax

-	testl	%eax, %eax

-	jnz	L(4x_vec_end)

-

-	addq	$(VEC_SIZE * 4), %rdi

-

-# ifndef USE_AS_STRNLEN

-	jmp	L(loop_4x_vec)

-# else

+# ifdef USE_AS_STRNLEN

+	/* Break if at end of length.  */

 	subq	$(VEC_SIZE * 4), %rsi

-	ja	L(loop_4x_vec)

-

-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)

+	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.

+	 */

+	vmovdqa	1(%rdi), %ymm1

+	VPMINU	(VEC_SIZE + 1)(%rdi), %ymm1, %ymm2

+	vmovdqa	(VEC_SIZE * 2 + 1)(%rdi), %ymm3

+	VPMINU	(VEC_SIZE * 3 + 1)(%rdi), %ymm3, %ymm4

+

+	VPMINU	%ymm2, %ymm4, %ymm5

+	VPCMPEQ	%ymm5, %ymm0, %ymm5

+	vpmovmskb	%ymm5, %ecx

-	VPCMPEQ (%rdi), %ymm0, %ymm1

-	vpmovmskb %ymm1, %eax

-	testl	%eax, %eax

-	jnz	L(first_vec_x0)

+	subq	$-(VEC_SIZE * 4), %rdi

+	testl	%ecx, %ecx

+	jz	L(loop_4x_vec)

-	VPCMPEQ VEC_SIZE(%rdi), %ymm0, %ymm1

-	vpmovmskb %ymm1, %eax

-	testl	%eax, %eax

-	jnz	L(first_vec_x1)

-	VPCMPEQ (VEC_SIZE * 2)(%rdi), %ymm0, %ymm1

-	vpmovmskb %ymm1, %eax

+	VPCMPEQ	%ymm1, %ymm0, %ymm1

+	vpmovmskb	%ymm1, %eax

+	subq	%rdx, %rdi

 	testl	%eax, %eax

+	jnz	L(last_vec_return_x0)

-	jnz	L(first_vec_x2_check)

-	subl	$VEC_SIZE, %esi

-	jle	L(max)

-

-	VPCMPEQ (VEC_SIZE * 3)(%rdi), %ymm0, %ymm1

-	vpmovmskb %ymm1, %eax

+	VPCMPEQ	%ymm2, %ymm0, %ymm2

+	vpmovmskb	%ymm2, %eax

 	testl	%eax, %eax

-

-	jnz	L(first_vec_x3_check)

-	movq	%r8, %rax

-#  ifdef USE_AS_WCSLEN

+	jnz	L(last_vec_return_x1)

+

+	/* Combine last 2 VEC.  */

+	VPCMPEQ	%ymm3, %ymm0, %ymm3

+	vpmovmskb	%ymm3, %eax

+	/* rcx has combined result from all 4 VEC. It will only be used if

+	   the first 3 other VEC all did not contain a match.  */

+	salq	$32, %rcx

+	orq	%rcx, %rax

+	tzcntq	%rax, %rax

+	subq	$(VEC_SIZE * 2 - 1), %rdi

+	addq	%rdi, %rax

+# ifdef USE_AS_WCSLEN

 	shrq	$2, %rax

-#  endif

+# endif

 	VZEROUPPER_RETURN

+

+# ifdef USE_AS_STRNLEN

 	.p2align 4

-L(last_2x_vec):

-	addl	$(VEC_SIZE * 2), %esi

-	VPCMPEQ (%rdi), %ymm0, %ymm1

-	vpmovmskb %ymm1, %eax

-	testl	%eax, %eax

+L(last_4x_vec_or_less_load):

+	/* Depending on entry adjust rdi / prepare first VEC in ymm1.  */

+	subq	$-(VEC_SIZE * 4), %rdi

+L(last_4x_vec_or_less_cmpeq):

+	VPCMPEQ	1(%rdi), %ymm0, %ymm1

+L(last_4x_vec_or_less):

-	jnz	L(first_vec_x0_check)

-	subl	$VEC_SIZE, %esi

-	jle	L(max)

+	vpmovmskb	%ymm1, %eax

+	/* If remaining length > VEC_SIZE * 2. This works if esi is off by

+	   VEC_SIZE * 4.  */

+	testl	$(VEC_SIZE * 2), %esi

+	jnz	L(last_4x_vec)

-	VPCMPEQ VEC_SIZE(%rdi), %ymm0, %ymm1

-	vpmovmskb %ymm1, %eax

+	/* length may have been negative or positive by an offset of

+	   VEC_SIZE * 4 depending on where this was called from. This fixes

+	   that.  */

+	andl	$(VEC_SIZE * 4 - 1), %esi

 	testl	%eax, %eax

-	jnz	L(first_vec_x1_check)

-	movq	%r8, %rax

-#  ifdef USE_AS_WCSLEN

-	shrq	$2, %rax

-#  endif

-	VZEROUPPER_RETURN

+	jnz	L(last_vec_x1_check)

-	.p2align 4

-L(first_vec_x0_check):

+	subl	$VEC_SIZE, %esi

+	jb	L(max)

+

+	VPCMPEQ	(VEC_SIZE + 1)(%rdi), %ymm0, %ymm1

+	vpmovmskb	%ymm1, %eax

 	tzcntl	%eax, %eax

 	/* Check the end of data.  */

-	cmpq	%rax, %rsi

-	jbe	L(max)

+	cmpl	%eax, %esi

+	jb	L(max)

+	subq	%rdx, %rdi

+	addl	$(VEC_SIZE + 1), %eax

 	addq	%rdi, %rax

-	subq	%rdx, %rax

 #  ifdef USE_AS_WCSLEN

 	shrq	$2, %rax

 #  endif

 	VZEROUPPER_RETURN

+# endif

 	.p2align 4

-L(first_vec_x1_check):

+L(last_vec_return_x0):

 	tzcntl	%eax, %eax

-	/* Check the end of data.  */

-	cmpq	%rax, %rsi

-	jbe	L(max)

-	addq	$VEC_SIZE, %rax

+	subq	$(VEC_SIZE * 4 - 1), %rdi

 	addq	%rdi, %rax

-	subq	%rdx, %rax

-#  ifdef USE_AS_WCSLEN

+# ifdef USE_AS_WCSLEN

 	shrq	$2, %rax

-#  endif

+# endif

 	VZEROUPPER_RETURN

 	.p2align 4

-L(first_vec_x2_check):

+L(last_vec_return_x1):

 	tzcntl	%eax, %eax

-	/* Check the end of data.  */

-	cmpq	%rax, %rsi

-	jbe	L(max)

-	addq	$(VEC_SIZE * 2), %rax

+	subq	$(VEC_SIZE * 3 - 1), %rdi

 	addq	%rdi, %rax

-	subq	%rdx, %rax

-#  ifdef USE_AS_WCSLEN

+# ifdef USE_AS_WCSLEN

 	shrq	$2, %rax

-#  endif

+# endif

 	VZEROUPPER_RETURN

+# ifdef USE_AS_STRNLEN

 	.p2align 4

-L(first_vec_x3_check):

+L(last_vec_x1_check):

+

 	tzcntl	%eax, %eax

 	/* Check the end of data.  */

-	cmpq	%rax, %rsi

-	jbe	L(max)

-	addq	$(VEC_SIZE * 3), %rax

+	cmpl	%eax, %esi

+	jb	L(max)

+	subq	%rdx, %rdi

+	incl	%eax

 	addq	%rdi, %rax

-	subq	%rdx, %rax

 #  ifdef USE_AS_WCSLEN

 	shrq	$2, %rax

 #  endif

 	VZEROUPPER_RETURN

-	.p2align 4

 L(max):

 	movq	%r8, %rax

+	VZEROUPPER_RETURN

+

+	.p2align 4

+L(last_4x_vec):

+	/* Test first 2x VEC normally.  */

+	testl	%eax, %eax

+	jnz	L(last_vec_x1)

+

+	VPCMPEQ	(VEC_SIZE + 1)(%rdi), %ymm0, %ymm1

+	vpmovmskb	%ymm1, %eax

+	testl	%eax, %eax

+	jnz	L(last_vec_x2)

+

+	/* Normalize length.  */

+	andl	$(VEC_SIZE * 4 - 1), %esi

+	VPCMPEQ	(VEC_SIZE * 2 + 1)(%rdi), %ymm0, %ymm1

+	vpmovmskb	%ymm1, %eax

+	testl	%eax, %eax

+	jnz	L(last_vec_x3)

+

+	subl	$(VEC_SIZE * 3), %esi

+	jb	L(max)

+

+	VPCMPEQ	(VEC_SIZE * 3 + 1)(%rdi), %ymm0, %ymm1

+	vpmovmskb	%ymm1, %eax

+	tzcntl	%eax, %eax

+	/* Check the end of data.  */

+	cmpl	%eax, %esi

+	jb	L(max)

+	subq	%rdx, %rdi

+	addl	$(VEC_SIZE * 3 + 1), %eax

+	addq	%rdi, %rax

 #  ifdef USE_AS_WCSLEN

 	shrq	$2, %rax

 #  endif

 	VZEROUPPER_RETURN

-	.p2align 4

-L(zero):

-	xorl	%eax, %eax

-	ret

-# endif

 	.p2align 4

-L(first_vec_x0):

+L(last_vec_x1):

+	/* essentially duplicates of first_vec_x1 but use 64 bit

+	   instructions.  */

 	tzcntl	%eax, %eax

+	subq	%rdx, %rdi

+	incl	%eax

 	addq	%rdi, %rax

-	subq	%rdx, %rax

-# ifdef USE_AS_WCSLEN

+#  ifdef USE_AS_WCSLEN

 	shrq	$2, %rax

-# endif

+#  endif

 	VZEROUPPER_RETURN

 	.p2align 4

-L(first_vec_x1):

+L(last_vec_x2):

+	/* essentially duplicates of first_vec_x1 but use 64 bit

+	   instructions.  */

 	tzcntl	%eax, %eax

-	addq	$VEC_SIZE, %rax

+	subq	%rdx, %rdi

+	addl	$(VEC_SIZE + 1), %eax

 	addq	%rdi, %rax

-	subq	%rdx, %rax

-# ifdef USE_AS_WCSLEN

+#  ifdef USE_AS_WCSLEN

 	shrq	$2, %rax

-# endif

+#  endif

 	VZEROUPPER_RETURN

 	.p2align 4

-L(first_vec_x2):

+L(last_vec_x3):

 	tzcntl	%eax, %eax

-	addq	$(VEC_SIZE * 2), %rax

+	subl	$(VEC_SIZE * 2), %esi

+	/* Check the end of data.  */

+	cmpl	%eax, %esi

+	jb	L(max_end)

+	subq	%rdx, %rdi

+	addl	$(VEC_SIZE * 2 + 1), %eax

 	addq	%rdi, %rax

-	subq	%rdx, %rax

-# ifdef USE_AS_WCSLEN

+#  ifdef USE_AS_WCSLEN

 	shrq	$2, %rax

-# endif

+#  endif

+	VZEROUPPER_RETURN

+L(max_end):

+	movq	%r8, %rax

 	VZEROUPPER_RETURN

+# endif

+	/* Cold case for crossing page with first load.	 */

 	.p2align 4

-L(4x_vec_end):

-	VPCMPEQ	%ymm1, %ymm0, %ymm1

-	vpmovmskb %ymm1, %eax

-	testl	%eax, %eax

-	jnz	L(first_vec_x0)

-	VPCMPEQ %ymm2, %ymm0, %ymm2

-	vpmovmskb %ymm2, %eax

+L(cross_page_boundary):

+	/* Align data to VEC_SIZE - 1.  */

+	orq	$(VEC_SIZE - 1), %rdi

+	VPCMPEQ	-(VEC_SIZE - 1)(%rdi), %ymm0, %ymm1

+	vpmovmskb	%ymm1, %eax

+	/* Remove the leading bytes. sarxl only uses bits [5:0] of COUNT

+	   so no need to manually mod rdx.  */

+	sarxl	%edx, %eax, %eax

+# ifdef USE_AS_STRNLEN