From acd575144cc6340edfbf0a0e0580e38344ab623a Mon Sep 17 00:00:00 2001

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

Date: Mon, 3 May 2021 03:01:58 -0400

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

No bug. This commit optimizes memchr-avx2.S. The optimizations include

replacing some branches with cmovcc, avoiding some branches entirely

in the less_4x_vec case, making the page cross logic less strict,

asaving a few instructions the in loop return loop. test-memchr,

test-rawmemchr, and test-wmemchr are all passing.

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

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

(cherry picked from commit acfd088a1963ba51cd83c78f95c0ab25ead79e04)

---

 sysdeps/x86_64/multiarch/memchr-avx2.S | 425 ++++++++++++++-----------

 1 file changed, 247 insertions(+), 178 deletions(-)

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

index cf893e77..b377f22e 100644

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

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

@@ -26,8 +26,22 @@

 # ifdef USE_AS_WMEMCHR

 #  define VPCMPEQ	vpcmpeqd

+#  define VPBROADCAST	vpbroadcastd

+#  define CHAR_SIZE	4

 # else

 #  define VPCMPEQ	vpcmpeqb

+#  define VPBROADCAST	vpbroadcastb

+#  define CHAR_SIZE	1

+# endif

+

+# ifdef USE_AS_RAWMEMCHR

+#  define ERAW_PTR_REG	ecx

+#  define RRAW_PTR_REG	rcx

+#  define ALGN_PTR_REG	rdi

+# else

+#  define ERAW_PTR_REG	edi

+#  define RRAW_PTR_REG	rdi

+#  define ALGN_PTR_REG	rcx

 # endif

 # ifndef VZEROUPPER

@@ -39,6 +53,7 @@

 # endif

 # define VEC_SIZE 32

+# define PAGE_SIZE 4096

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

 ENTRY (MEMCHR)

@@ -47,295 +62,349 @@ ENTRY (MEMCHR)

 	test	%RDX_LP, %RDX_LP

 	jz	L(null)

 # endif

-	movl	%edi, %ecx

-	/* Broadcast CHAR to YMM0.  */

-	vmovd	%esi, %xmm0

 # ifdef USE_AS_WMEMCHR

 	shl	$2, %RDX_LP

-	vpbroadcastd %xmm0, %ymm0

 # else

 #  ifdef __ILP32__

 	/* Clear the upper 32 bits.  */

 	movl	%edx, %edx

 #  endif

-	vpbroadcastb %xmm0, %ymm0

 # endif

+	/* Broadcast CHAR to YMMMATCH.  */

+	vmovd	%esi, %xmm0

+	VPBROADCAST %xmm0, %ymm0

 	/* 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)

+	movl	%edi, %eax

+	andl	$(PAGE_SIZE - 1), %eax

+	cmpl	$(PAGE_SIZE - VEC_SIZE), %eax

+	ja	L(cross_page_boundary)

 	/* Check the first VEC_SIZE bytes.  */

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

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

 	vpmovmskb %ymm1, %eax

-	testl	%eax, %eax

-

 # ifndef USE_AS_RAWMEMCHR

-	jnz	L(first_vec_x0_check)

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

-	subq	$VEC_SIZE, %rdx

-	jbe	L(zero)

-# else

-	jnz	L(first_vec_x0)

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

+	cmpq	$VEC_SIZE, %rdx

+	jbe	L(first_vec_x0)

 # endif

-

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

-	addq	$VEC_SIZE, %rdi

-	andl	$(VEC_SIZE - 1), %ecx

-	andq	$-VEC_SIZE, %rdi

+	testl	%eax, %eax

+	jz	L(aligned_more)

+	tzcntl	%eax, %eax

+	addq	%rdi, %rax

+	VZEROUPPER_RETURN

 # ifndef USE_AS_RAWMEMCHR

-	/* Adjust length.  */

-	addq	%rcx, %rdx

+	.p2align 5

+L(first_vec_x0):

+	/* Check if first match was before length.  */

+	tzcntl	%eax, %eax

+	xorl	%ecx, %ecx

+	cmpl	%eax, %edx

+	leaq	(%rdi, %rax), %rax

+	cmovle	%rcx, %rax

+	VZEROUPPER_RETURN

-	subq	$(VEC_SIZE * 4), %rdx

-	jbe	L(last_4x_vec_or_less)

+L(null):

+	xorl	%eax, %eax

+	ret

 # endif

-	jmp	L(more_4x_vec)

-

 	.p2align 4

-L(cros_page_boundary):

-	andl	$(VEC_SIZE - 1), %ecx

-	andq	$-VEC_SIZE, %rdi

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

+L(cross_page_boundary):

+	/* Save pointer before aligning as its original value is necessary

+	   for computer return address if byte is found or adjusting length

+	   if it is not and this is memchr.  */

+	movq	%rdi, %rcx

+	/* Align data to VEC_SIZE - 1. ALGN_PTR_REG is rcx for memchr and

+	   rdi for rawmemchr.  */

+	orq	$(VEC_SIZE - 1), %ALGN_PTR_REG

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

 	vpmovmskb %ymm1, %eax

+# ifndef USE_AS_RAWMEMCHR

+	/* Calculate length until end of page (length checked for a

+	   match).  */

+	leaq	1(%ALGN_PTR_REG), %rsi

+	subq	%RRAW_PTR_REG, %rsi

+# endif

 	/* Remove the leading bytes.  */

-	sarl	%cl, %eax

-	testl	%eax, %eax

-	jz	L(aligned_more)

-	tzcntl	%eax, %eax

+	sarxl	%ERAW_PTR_REG, %eax, %eax

 # ifndef USE_AS_RAWMEMCHR

 	/* Check the end of data.  */

-	cmpq	%rax, %rdx

-	jbe	L(zero)

+	cmpq	%rsi, %rdx

+	jbe	L(first_vec_x0)

 # endif

-	addq	%rdi, %rax

-	addq	%rcx, %rax

+	testl	%eax, %eax

+	jz	L(cross_page_continue)

+	tzcntl	%eax, %eax

+	addq	%RRAW_PTR_REG, %rax

 L(return_vzeroupper):

 	ZERO_UPPER_VEC_REGISTERS_RETURN

 	.p2align 4

-L(aligned_more):

-# ifndef USE_AS_RAWMEMCHR

-        /* Calculate "rdx + rcx - VEC_SIZE" with "rdx - (VEC_SIZE - rcx)"

-	   instead of "(rdx + rcx) - VEC_SIZE" to void possible addition

-	   overflow.  */

-	negq	%rcx

-	addq	$VEC_SIZE, %rcx

+L(first_vec_x1):

+	tzcntl	%eax, %eax

+	incq	%rdi

+	addq	%rdi, %rax

+	VZEROUPPER_RETURN

-	/* Check the end of data.  */

-	subq	%rcx, %rdx

-	jbe	L(zero)

-# endif

+	.p2align 4

+L(first_vec_x2):

+	tzcntl	%eax, %eax

+	addq	$(VEC_SIZE + 1), %rdi

+	addq	%rdi, %rax

+	VZEROUPPER_RETURN

+

+	.p2align 4

+L(first_vec_x3):

+	tzcntl	%eax, %eax

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

+	addq	%rdi, %rax

+	VZEROUPPER_RETURN

-	addq	$VEC_SIZE, %rdi

-# ifndef USE_AS_RAWMEMCHR

-	subq	$(VEC_SIZE * 4), %rdx

-	jbe	L(last_4x_vec_or_less)

-# endif

+	.p2align 4

+L(first_vec_x4):

+	tzcntl	%eax, %eax

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

+	addq	%rdi, %rax

+	VZEROUPPER_RETURN

-L(more_4x_vec):

+	.p2align 4

+L(aligned_more):

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

 	   since data is only aligned to VEC_SIZE.  */

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

-	vpmovmskb %ymm1, %eax

-	testl	%eax, %eax

-	jnz	L(first_vec_x0)

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

+# ifndef USE_AS_RAWMEMCHR

+L(cross_page_continue):

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

+	xorl	%ecx, %ecx

+	subl	%edi, %ecx

+	orq	$(VEC_SIZE - 1), %rdi

+	/* esi is for adjusting length to see if near the end.  */

+	leal	(VEC_SIZE * 4 + 1)(%rdi, %rcx), %esi

+# else

+	orq	$(VEC_SIZE - 1), %rdi

+L(cross_page_continue):

+# endif

+	/* Load first VEC regardless.  */

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

 	vpmovmskb %ymm1, %eax

+# ifndef USE_AS_RAWMEMCHR

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

+	subq	%rsi, %rdx

+	jbe	L(last_4x_vec_or_less)

+# endif

 	testl	%eax, %eax

 	jnz	L(first_vec_x1)

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

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

 	vpmovmskb %ymm1, %eax

 	testl	%eax, %eax

 	jnz	L(first_vec_x2)

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

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

 	vpmovmskb %ymm1, %eax

 	testl	%eax, %eax

 	jnz	L(first_vec_x3)

-	addq	$(VEC_SIZE * 4), %rdi

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

+	vpmovmskb %ymm1, %eax

+	testl	%eax, %eax

+	jnz	L(first_vec_x4)

 # ifndef USE_AS_RAWMEMCHR

+	/* Check if at last VEC_SIZE * 4 length.  */

 	subq	$(VEC_SIZE * 4), %rdx

-	jbe	L(last_4x_vec_or_less)

-# endif

-

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

-	movq	%rdi, %rcx

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

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

-

-# ifndef USE_AS_RAWMEMCHR

-	/* Adjust length.  */

+	jbe	L(last_4x_vec_or_less_cmpeq)

+	/* Align data to VEC_SIZE * 4 - 1 for the loop and readjust

+	   length.  */

+	incq	%rdi

+	movl	%edi, %ecx

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

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

 	addq	%rcx, %rdx

+# else

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

+	incq	%rdi

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

 # endif

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

 	.p2align 4

 L(loop_4x_vec):

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

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

-	VPCMPEQ VEC_SIZE(%rdi), %ymm0, %ymm2

-	VPCMPEQ (VEC_SIZE * 2)(%rdi), %ymm0, %ymm3

-	VPCMPEQ (VEC_SIZE * 3)(%rdi), %ymm0, %ymm4

-

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

+	VPCMPEQ	(VEC_SIZE + 1)(%rdi), %ymm0, %ymm2

+	VPCMPEQ	(VEC_SIZE * 2 + 1)(%rdi), %ymm0, %ymm3

+	VPCMPEQ	(VEC_SIZE * 3 + 1)(%rdi), %ymm0, %ymm4

 	vpor	%ymm1, %ymm2, %ymm5

 	vpor	%ymm3, %ymm4, %ymm6

 	vpor	%ymm5, %ymm6, %ymm5

-	vpmovmskb %ymm5, %eax

-	testl	%eax, %eax

-	jnz	L(4x_vec_end)

-

-	addq	$(VEC_SIZE * 4), %rdi

-

+	vpmovmskb %ymm5, %ecx

 # ifdef USE_AS_RAWMEMCHR

-	jmp	L(loop_4x_vec)

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

+	testl	%ecx, %ecx

+	jz	L(loop_4x_vec)

 # else

-	subq	$(VEC_SIZE * 4), %rdx

-	ja	L(loop_4x_vec)

+	testl	%ecx, %ecx

+	jnz	L(loop_4x_vec_end)

-L(last_4x_vec_or_less):

-	/* Less than 4 * VEC and aligned to VEC_SIZE.  */

-	addl	$(VEC_SIZE * 2), %edx

-	jle	L(last_2x_vec)

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

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

-	vpmovmskb %ymm1, %eax

-	testl	%eax, %eax

-	jnz	L(first_vec_x0)

+	subq	$(VEC_SIZE * 4), %rdx

+	ja	L(loop_4x_vec)

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

+	/* Fall through into less than 4 remaining vectors of length case.

+	 */

+	VPCMPEQ	(VEC_SIZE * 0 + 1)(%rdi), %ymm0, %ymm1

 	vpmovmskb %ymm1, %eax

+	.p2align 4

+L(last_4x_vec_or_less):

+	/* Check if first VEC contained match.  */

 	testl	%eax, %eax

-	jnz	L(first_vec_x1)

+	jnz	L(first_vec_x1_check)

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

-	vpmovmskb %ymm1, %eax

-	testl	%eax, %eax

+	/* If remaining length > VEC_SIZE * 2.  */

+	addl	$(VEC_SIZE * 2), %edx

+	jg	L(last_4x_vec)

-	jnz	L(first_vec_x2_check)

-	subl	$VEC_SIZE, %edx

-	jle	L(zero)

+L(last_2x_vec):

+	/* If remaining length < VEC_SIZE.  */

+	addl	$VEC_SIZE, %edx

+	jle	L(zero_end)

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

+	/* Check VEC2 and compare any match with remaining length.  */

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

 	vpmovmskb %ymm1, %eax

-	testl	%eax, %eax

-

-	jnz	L(first_vec_x3_check)

-	xorl	%eax, %eax

+	tzcntl	%eax, %eax

+	cmpl	%eax, %edx

+	jbe	L(set_zero_end)

+	addq	$(VEC_SIZE + 1), %rdi

+	addq	%rdi, %rax

+L(zero_end):

 	VZEROUPPER_RETURN

 	.p2align 4

-L(last_2x_vec):

-	addl	$(VEC_SIZE * 2), %edx

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

+L(loop_4x_vec_end):

+# endif

+	/* rawmemchr will fall through into this if match was found in

+	   loop.  */

+

 	vpmovmskb %ymm1, %eax

 	testl	%eax, %eax

+	jnz	L(last_vec_x1_return)

-	jnz	L(first_vec_x0_check)

-	subl	$VEC_SIZE, %edx

-	jle	L(zero)

-

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

-	vpmovmskb %ymm1, %eax

+	vpmovmskb %ymm2, %eax

 	testl	%eax, %eax

-	jnz	L(first_vec_x1_check)

-	xorl	%eax, %eax

-	VZEROUPPER_RETURN

+	jnz	L(last_vec_x2_return)

-	.p2align 4

-L(first_vec_x0_check):

-	tzcntl	%eax, %eax

-	/* Check the end of data.  */

-	cmpq	%rax, %rdx

-	jbe	L(zero)

+	vpmovmskb %ymm3, %eax

+	/* Combine VEC3 matches (eax) with VEC4 matches (ecx).  */

+	salq	$32, %rcx

+	orq	%rcx, %rax

+	tzcntq	%rax, %rax

+# ifdef USE_AS_RAWMEMCHR

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

+# else

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

+# endif

 	addq	%rdi, %rax

 	VZEROUPPER_RETURN

+# ifndef USE_AS_RAWMEMCHR

 	.p2align 4

 L(first_vec_x1_check):

 	tzcntl	%eax, %eax

-	/* Check the end of data.  */

-	cmpq	%rax, %rdx

-	jbe	L(zero)

-	addq	$VEC_SIZE, %rax

+	/* Adjust length.  */

+	subl	$-(VEC_SIZE * 4), %edx

+	/* Check if match within remaining length.  */

+	cmpl	%eax, %edx

+	jbe	L(set_zero_end)

+	incq	%rdi

 	addq	%rdi, %rax

 	VZEROUPPER_RETURN

+	.p2align 4

+L(set_zero_end):

+	xorl	%eax, %eax

+	VZEROUPPER_RETURN

+# endif

 	.p2align 4

-L(first_vec_x2_check):

+L(last_vec_x1_return):

 	tzcntl	%eax, %eax

-	/* Check the end of data.  */

-	cmpq	%rax, %rdx

-	jbe	L(zero)

-	addq	$(VEC_SIZE * 2), %rax

+# ifdef USE_AS_RAWMEMCHR

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

+# else

+	incq	%rdi

+# endif

 	addq	%rdi, %rax

 	VZEROUPPER_RETURN

 	.p2align 4

-L(first_vec_x3_check):

+L(last_vec_x2_return):

 	tzcntl	%eax, %eax

-	/* Check the end of data.  */

-	cmpq	%rax, %rdx

-	jbe	L(zero)

-	addq	$(VEC_SIZE * 3), %rax

+# ifdef USE_AS_RAWMEMCHR

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

+# else

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

+# endif

 	addq	%rdi, %rax

 	VZEROUPPER_RETURN

+# ifndef USE_AS_RAWMEMCHR

 	.p2align 4

-L(zero):

-	xorl	%eax, %eax

-	jmp     L(return_vzeroupper)

+L(last_4x_vec_or_less_cmpeq):

+	VPCMPEQ	(VEC_SIZE * 4 + 1)(%rdi), %ymm0, %ymm1

+	vpmovmskb %ymm1, %eax

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

+	/* Check first VEC regardless.  */

+	testl	%eax, %eax

+	jnz	L(first_vec_x1_check)

+	/* If remaining length <= CHAR_PER_VEC * 2.  */

+	addl	$(VEC_SIZE * 2), %edx

+	jle	L(last_2x_vec)

 	.p2align 4

-L(null):

-	xorl	%eax, %eax

-	ret

-# endif

+L(last_4x_vec):

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

+	vpmovmskb %ymm1, %eax

+	testl	%eax, %eax

+	jnz	L(last_vec_x2_return)

-	.p2align 4

-L(first_vec_x0):

-	tzcntl	%eax, %eax

-	addq	%rdi, %rax

-	VZEROUPPER_RETURN

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

+	vpmovmskb %ymm1, %eax

-	.p2align 4

-L(first_vec_x1):

-	tzcntl	%eax, %eax

-	addq	$VEC_SIZE, %rax

-	addq	%rdi, %rax

-	VZEROUPPER_RETURN

+	/* Create mask for possible matches within remaining length.  */

+	movq	$-1, %rcx

+	bzhiq	%rdx, %rcx, %rcx

-	.p2align 4

-L(first_vec_x2):

+	/* Test matches in data against length match.  */

+	andl	%ecx, %eax

+	jnz	L(last_vec_x3)

+

+	/* if remaining length <= VEC_SIZE * 3 (Note this is after

+	   remaining length was found to be > VEC_SIZE * 2.  */

+	subl	$VEC_SIZE, %edx

+	jbe	L(zero_end2)

+

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

+	vpmovmskb %ymm1, %eax

+	/* Shift remaining length mask for last VEC.  */

+	shrq	$32, %rcx

+	andl	%ecx, %eax

+	jz	L(zero_end2)

 	tzcntl	%eax, %eax

-	addq	$(VEC_SIZE * 2), %rax

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

 	addq	%rdi, %rax

+L(zero_end2):

 	VZEROUPPER_RETURN

 	.p2align 4

-L(4x_vec_end):

-	vpmovmskb %ymm1, %eax

-	testl	%eax, %eax

-	jnz	L(first_vec_x0)

-	vpmovmskb %ymm2, %eax

-	testl	%eax, %eax

-	jnz	L(first_vec_x1)

-	vpmovmskb %ymm3, %eax

-	testl	%eax, %eax

-	jnz	L(first_vec_x2)

-	vpmovmskb %ymm4, %eax

-	testl	%eax, %eax

-L(first_vec_x3):

+L(last_vec_x3):

 	tzcntl	%eax, %eax

-	addq	$(VEC_SIZE * 3), %rax

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

 	addq	%rdi, %rax

 	VZEROUPPER_RETURN

+# endif

 END (MEMCHR)

 #endif

-- 

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