From 93b1c47bd092f8e1444a10b5d6ec20e44d66459a Mon Sep 17 00:00:00 2001

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

Date: Fri, 23 Apr 2021 15:56:24 -0400

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

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

small things such as save an ALU in the alignment process, saving a

few instructions in the loop return, saving some bytes in the main

loop, and increasing the ILP in the return cases. test-strchr,

test-strchrnul, test-wcschr, and test-wcschrnul are all passing.

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

(cherry picked from commit ccabe7971f508709d034b63b8672f6f751a3d356)

---

 sysdeps/x86_64/multiarch/strchr-avx2.S | 290 +++++++++++++++----------

 1 file changed, 170 insertions(+), 120 deletions(-)

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

index 919d256c..5884726b 100644

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

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

@@ -49,133 +49,144 @@

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

 ENTRY (STRCHR)

-	movl	%edi, %ecx

-# ifndef USE_AS_STRCHRNUL

-	xorl	%edx, %edx

-# endif

-

 	/* Broadcast CHAR to YMM0.	*/

 	vmovd	%esi, %xmm0

+	movl	%edi, %eax

+	andl	$(PAGE_SIZE - 1), %eax

+	VPBROADCAST	%xmm0, %ymm0

 	vpxor	%xmm9, %xmm9, %xmm9

-	VPBROADCAST %xmm0, %ymm0

 	/* Check if we cross page boundary with one vector load.  */

-	andl	$(PAGE_SIZE - 1), %ecx

-	cmpl	$(PAGE_SIZE - VEC_SIZE), %ecx

-	ja  L(cross_page_boundary)

+	cmpl	$(PAGE_SIZE - VEC_SIZE), %eax

+	ja	L(cross_page_boundary)

 	/* Check the first VEC_SIZE bytes.	Search for both CHAR and the

 	   null byte.  */

 	vmovdqu	(%rdi), %ymm8

-	VPCMPEQ %ymm8, %ymm0, %ymm1

-	VPCMPEQ %ymm8, %ymm9, %ymm2

+	VPCMPEQ	%ymm8, %ymm0, %ymm1

+	VPCMPEQ	%ymm8, %ymm9, %ymm2

 	vpor	%ymm1, %ymm2, %ymm1

 	vpmovmskb %ymm1, %eax

 	testl	%eax, %eax

-	jz	L(more_vecs)

+	jz	L(aligned_more)

 	tzcntl	%eax, %eax

+# ifndef USE_AS_STRCHRNUL

 	/* Found CHAR or the null byte.	 */

+	cmp	(%rdi, %rax), %CHAR_REG

+	jne	L(zero)

+# endif

 	addq	%rdi, %rax

+	VZEROUPPER_RETURN

+

+	/* .p2align 5 helps keep performance more consistent if ENTRY()

+	   alignment % 32 was either 16 or 0. As well this makes the

+	   alignment % 32 of the loop_4x_vec fixed which makes tuning it

+	   easier.  */

+	.p2align 5

+L(first_vec_x4):

+	tzcntl	%eax, %eax

+	addq	$(VEC_SIZE * 3 + 1), %rdi

 # ifndef USE_AS_STRCHRNUL

-	cmp (%rax), %CHAR_REG

-	cmovne	%rdx, %rax

+	/* Found CHAR or the null byte.	 */

+	cmp	(%rdi, %rax), %CHAR_REG

+	jne	L(zero)

 # endif

-L(return_vzeroupper):

-	ZERO_UPPER_VEC_REGISTERS_RETURN

-

-	.p2align 4

-L(more_vecs):

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

-	andq	$-VEC_SIZE, %rdi

-L(aligned_more):

-

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

-	   since data is only aligned to VEC_SIZE.	*/

-	vmovdqa	VEC_SIZE(%rdi), %ymm8

-	addq	$VEC_SIZE, %rdi

-	VPCMPEQ %ymm8, %ymm0, %ymm1

-	VPCMPEQ %ymm8, %ymm9, %ymm2

-	vpor	%ymm1, %ymm2, %ymm1

-	vpmovmskb %ymm1, %eax

-	testl	%eax, %eax

-	jnz	L(first_vec_x0)

-

-	vmovdqa	VEC_SIZE(%rdi), %ymm8

-	VPCMPEQ %ymm8, %ymm0, %ymm1

-	VPCMPEQ %ymm8, %ymm9, %ymm2

-	vpor	%ymm1, %ymm2, %ymm1

-	vpmovmskb %ymm1, %eax

-	testl	%eax, %eax

-	jnz	L(first_vec_x1)

-

-	vmovdqa	(VEC_SIZE * 2)(%rdi), %ymm8

-	VPCMPEQ %ymm8, %ymm0, %ymm1

-	VPCMPEQ %ymm8, %ymm9, %ymm2

-	vpor	%ymm1, %ymm2, %ymm1

-	vpmovmskb %ymm1, %eax

-	testl	%eax, %eax

-	jnz	L(first_vec_x2)

-

-	vmovdqa	(VEC_SIZE * 3)(%rdi), %ymm8

-	VPCMPEQ %ymm8, %ymm0, %ymm1

-	VPCMPEQ %ymm8, %ymm9, %ymm2

-	vpor	%ymm1, %ymm2, %ymm1

-	vpmovmskb %ymm1, %eax

-	testl	%eax, %eax

-	jz	L(prep_loop_4x)

+	addq	%rdi, %rax

+	VZEROUPPER_RETURN

-	tzcntl	%eax, %eax

-	leaq	(VEC_SIZE * 3)(%rdi, %rax), %rax

 # ifndef USE_AS_STRCHRNUL

-	cmp (%rax), %CHAR_REG

-	cmovne	%rdx, %rax

+L(zero):

+	xorl	%eax, %eax

+	VZEROUPPER_RETURN

 # endif

-	VZEROUPPER

-	ret

+

 	.p2align 4

-L(first_vec_x0):

+L(first_vec_x1):

 	tzcntl	%eax, %eax

-	/* Found CHAR or the null byte.	 */

-	addq	%rdi, %rax

+	incq	%rdi

 # ifndef USE_AS_STRCHRNUL

-	cmp (%rax), %CHAR_REG

-	cmovne	%rdx, %rax

+	/* Found CHAR or the null byte.	 */

+	cmp	(%rdi, %rax), %CHAR_REG

+	jne	L(zero)

 # endif

+	addq	%rdi, %rax

 	VZEROUPPER_RETURN

 	.p2align 4

-L(first_vec_x1):

+L(first_vec_x2):

 	tzcntl	%eax, %eax

-	leaq	VEC_SIZE(%rdi, %rax), %rax

+	addq	$(VEC_SIZE + 1), %rdi

 # ifndef USE_AS_STRCHRNUL

-	cmp (%rax), %CHAR_REG

-	cmovne	%rdx, %rax

+	/* Found CHAR or the null byte.	 */

+	cmp	(%rdi, %rax), %CHAR_REG

+	jne	L(zero)

 # endif

+	addq	%rdi, %rax

 	VZEROUPPER_RETURN

 	.p2align 4

-L(first_vec_x2):

+L(first_vec_x3):

 	tzcntl	%eax, %eax

-	/* Found CHAR or the null byte.	 */

-	leaq	(VEC_SIZE * 2)(%rdi, %rax), %rax

+	addq	$(VEC_SIZE * 2 + 1), %rdi

 # ifndef USE_AS_STRCHRNUL

-	cmp (%rax), %CHAR_REG

-	cmovne	%rdx, %rax

+	/* Found CHAR or the null byte.	 */

+	cmp	(%rdi, %rax), %CHAR_REG

+	jne	L(zero)

 # endif

+	addq	%rdi, %rax

 	VZEROUPPER_RETURN

-L(prep_loop_4x):

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

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

+	.p2align 4

+L(aligned_more):

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

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

+	   on x4 check.  */

+	orq	$(VEC_SIZE - 1), %rdi

+L(cross_page_continue):

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

+	   since data is only aligned to VEC_SIZE.  */

+	vmovdqa	1(%rdi), %ymm8

+	VPCMPEQ	%ymm8, %ymm0, %ymm1

+	VPCMPEQ	%ymm8, %ymm9, %ymm2

+	vpor	%ymm1, %ymm2, %ymm1

+	vpmovmskb %ymm1, %eax

+	testl	%eax, %eax

+	jnz	L(first_vec_x1)

+

+	vmovdqa	(VEC_SIZE + 1)(%rdi), %ymm8

+	VPCMPEQ	%ymm8, %ymm0, %ymm1

+	VPCMPEQ	%ymm8, %ymm9, %ymm2

+	vpor	%ymm1, %ymm2, %ymm1

+	vpmovmskb %ymm1, %eax

+	testl	%eax, %eax

+	jnz	L(first_vec_x2)

+

+	vmovdqa	(VEC_SIZE * 2 + 1)(%rdi), %ymm8

+	VPCMPEQ	%ymm8, %ymm0, %ymm1

+	VPCMPEQ	%ymm8, %ymm9, %ymm2

+	vpor	%ymm1, %ymm2, %ymm1

+	vpmovmskb %ymm1, %eax

+	testl	%eax, %eax

+	jnz	L(first_vec_x3)

+	vmovdqa	(VEC_SIZE * 3 + 1)(%rdi), %ymm8

+	VPCMPEQ	%ymm8, %ymm0, %ymm1

+	VPCMPEQ	%ymm8, %ymm9, %ymm2

+	vpor	%ymm1, %ymm2, %ymm1

+	vpmovmskb %ymm1, %eax

+	testl	%eax, %eax

+	jnz	L(first_vec_x4)

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

+	addq	$(VEC_SIZE * 4 + 1), %rdi

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

 	.p2align 4

 L(loop_4x_vec):

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

-	vmovdqa	(VEC_SIZE * 4)(%rdi), %ymm5

-	vmovdqa	(VEC_SIZE * 5)(%rdi), %ymm6

-	vmovdqa	(VEC_SIZE * 6)(%rdi), %ymm7

-	vmovdqa	(VEC_SIZE * 7)(%rdi), %ymm8

+	vmovdqa	(%rdi), %ymm5

+	vmovdqa	(VEC_SIZE)(%rdi), %ymm6

+	vmovdqa	(VEC_SIZE * 2)(%rdi), %ymm7

+	vmovdqa	(VEC_SIZE * 3)(%rdi), %ymm8

 	/* Leaves only CHARS matching esi as 0.	 */

 	vpxor	%ymm5, %ymm0, %ymm1

@@ -191,63 +202,102 @@ L(loop_4x_vec):

 	VPMINU	%ymm1, %ymm2, %ymm5

 	VPMINU	%ymm3, %ymm4, %ymm6

-	VPMINU	%ymm5, %ymm6, %ymm5

+	VPMINU	%ymm5, %ymm6, %ymm6

-	VPCMPEQ %ymm5, %ymm9, %ymm5

-	vpmovmskb %ymm5, %eax

+	VPCMPEQ	%ymm6, %ymm9, %ymm6

+	vpmovmskb %ymm6, %ecx

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

+	testl	%ecx, %ecx

+	jz	L(loop_4x_vec)

-	addq	$(VEC_SIZE * 4), %rdi

-	testl	%eax, %eax

-	jz  L(loop_4x_vec)

-	VPCMPEQ %ymm1, %ymm9, %ymm1

+	VPCMPEQ	%ymm1, %ymm9, %ymm1

 	vpmovmskb %ymm1, %eax

 	testl	%eax, %eax

-	jnz	L(first_vec_x0)

+	jnz	L(last_vec_x0)

+

-	VPCMPEQ %ymm2, %ymm9, %ymm2

+	VPCMPEQ	%ymm5, %ymm9, %ymm2

 	vpmovmskb %ymm2, %eax

 	testl	%eax, %eax

-	jnz	L(first_vec_x1)

+	jnz	L(last_vec_x1)

+

+	VPCMPEQ	%ymm3, %ymm9, %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), %rdi

+# ifndef USE_AS_STRCHRNUL

+	/* Found CHAR or the null byte.	 */

+	cmp	(%rdi, %rax), %CHAR_REG

+	jne	L(zero_end)

+# endif

+	addq	%rdi, %rax

+	VZEROUPPER_RETURN

+

+

+	.p2align 4

+L(last_vec_x0):

+	tzcntl	%eax, %eax

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

+# ifndef USE_AS_STRCHRNUL

+	/* Found CHAR or the null byte.	 */

+	cmp	(%rdi, %rax), %CHAR_REG

+	jne	L(zero_end)

+# endif

+	addq	%rdi, %rax

+	VZEROUPPER_RETURN

-	VPCMPEQ %ymm3, %ymm9, %ymm3

-	VPCMPEQ %ymm4, %ymm9, %ymm4

-	vpmovmskb %ymm3, %ecx

-	vpmovmskb %ymm4, %eax

-	salq	$32, %rax

-	orq %rcx, %rax

-	tzcntq  %rax, %rax

-	leaq	(VEC_SIZE * 2)(%rdi, %rax), %rax

 # ifndef USE_AS_STRCHRNUL

-	cmp (%rax), %CHAR_REG

-	cmovne	%rdx, %rax

+L(zero_end):

+	xorl	%eax, %eax

+	VZEROUPPER_RETURN

 # endif

-	VZEROUPPER

-	ret

+

+	.p2align 4

+L(last_vec_x1):

+	tzcntl	%eax, %eax

+	subq	$(VEC_SIZE * 3), %rdi

+# ifndef USE_AS_STRCHRNUL

+	/* Found CHAR or the null byte.	 */

+	cmp	(%rdi, %rax), %CHAR_REG

+	jne	L(zero_end)

+# endif

+	addq	%rdi, %rax

+	VZEROUPPER_RETURN

+

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

 	.p2align 4

 L(cross_page_boundary):

-	andq	$-VEC_SIZE, %rdi

-	andl	$(VEC_SIZE - 1), %ecx

-

-	vmovdqa	(%rdi), %ymm8

-	VPCMPEQ %ymm8, %ymm0, %ymm1

-	VPCMPEQ %ymm8, %ymm9, %ymm2

+	movq	%rdi, %rdx

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

+	orq	$(VEC_SIZE - 1), %rdi

+	vmovdqa	-(VEC_SIZE - 1)(%rdi), %ymm8

+	VPCMPEQ	%ymm8, %ymm0, %ymm1

+	VPCMPEQ	%ymm8, %ymm9, %ymm2

 	vpor	%ymm1, %ymm2, %ymm1

 	vpmovmskb %ymm1, %eax

-	/* Remove the leading bits.	 */

-	sarxl	%ecx, %eax, %eax

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

+	   so no need to manually mod edx.  */

+	sarxl	%edx, %eax, %eax

 	testl	%eax, %eax

-	jz	L(aligned_more)

+	jz	L(cross_page_continue)

 	tzcntl	%eax, %eax

-	addq	%rcx, %rdi

-	addq	%rdi, %rax

 # ifndef USE_AS_STRCHRNUL

-	cmp (%rax), %CHAR_REG

-	cmovne	%rdx, %rax

+	xorl	%ecx, %ecx

+	/* Found CHAR or the null byte.	 */

+	cmp	(%rdx, %rax), %CHAR_REG

+	leaq	(%rdx, %rax), %rax

+	cmovne	%rcx, %rax

+# else

+	addq	%rdx, %rax

 # endif

-	VZEROUPPER_RETURN

+L(return_vzeroupper):

+	ZERO_UPPER_VEC_REGISTERS_RETURN

 END (STRCHR)

 # endif

-- 

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