From 1f745ecc2109890886b161d4791e1406fdfc29b8 Mon Sep 17 00:00:00 2001
From: noah <goldstein.w.n@gmail.com>
Date: Wed, 3 Feb 2021 00:38:59 -0500
Subject: [PATCH] x86-64: Refactor and improve performance of strchr-avx2.S
Content-type: text/plain; charset=UTF-8

No bug. Just seemed the performance could be improved a bit. Observed
and expected behavior are unchanged. Optimized body of main
loop. Updated page cross logic and optimized accordingly. Made a few
minor instruction selection modifications. No regressions in test
suite. Both test-strchrnul and test-strchr passed.
---
 sysdeps/x86_64/multiarch/strchr-avx2.S | 225 ++++++++++++-------------
 sysdeps/x86_64/multiarch/strchr.c      |   4 +-
 2 files changed, 114 insertions(+), 115 deletions(-)

Conflicts:
	sysdeps/x86_64/multiarch/strchr.c
	(account for missing upstream macros)

diff --git a/sysdeps/x86_64/multiarch/strchr-avx2.S b/sysdeps/x86_64/multiarch/strchr-avx2.S
index da7d2620..919d256c 100644
--- a/sysdeps/x86_64/multiarch/strchr-avx2.S
+++ b/sysdeps/x86_64/multiarch/strchr-avx2.S
@@ -27,10 +27,12 @@
 # ifdef USE_AS_WCSCHR
 #  define VPBROADCAST	vpbroadcastd
 #  define VPCMPEQ	vpcmpeqd
+#  define VPMINU	vpminud
 #  define CHAR_REG	esi
 # else
 #  define VPBROADCAST	vpbroadcastb
 #  define VPCMPEQ	vpcmpeqb
+#  define VPMINU	vpminub
 #  define CHAR_REG	sil
 # endif
 
@@ -43,71 +45,54 @@
 # endif
 
 # define VEC_SIZE 32
+# define PAGE_SIZE 4096
 
 	.section SECTION(.text),"ax",@progbits
 ENTRY (STRCHR)
 	movl	%edi, %ecx
-	/* Broadcast CHAR to YMM0.  */
+# ifndef USE_AS_STRCHRNUL
+	xorl	%edx, %edx
+# endif
+
+	/* Broadcast CHAR to YMM0.	*/
 	vmovd	%esi, %xmm0
 	vpxor	%xmm9, %xmm9, %xmm9
 	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)
 
-	/* 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
-	vpor	%ymm1, %ymm2, %ymm1
-	vpmovmskb %ymm1, %eax
-	testl	%eax, %eax
-	jnz	L(first_vec_x0)
+	/* 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)
 
-	/* Align data for aligned loads in the loop.  */
-	addq	$VEC_SIZE, %rdi
-	andl	$(VEC_SIZE - 1), %ecx
-	andq	$-VEC_SIZE, %rdi
-
-	jmp	L(more_4x_vec)
-
-	.p2align 4
-L(cros_page_boundary):
-	andl	$(VEC_SIZE - 1), %ecx
-	andq	$-VEC_SIZE, %rdi
+	/* 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
 	vpor	%ymm1, %ymm2, %ymm1
 	vpmovmskb %ymm1, %eax
-	/* Remove the leading bytes.  */
-	sarl	%cl, %eax
 	testl	%eax, %eax
-	jz	L(aligned_more)
-	/* Found CHAR or the null byte.  */
+	jz	L(more_vecs)
 	tzcntl	%eax, %eax
-	addq	%rcx, %rax
-# ifdef USE_AS_STRCHRNUL
+	/* Found CHAR or the null byte.	 */
 	addq	%rdi, %rax
-# else
-	xorl	%edx, %edx
-	leaq	(%rdi, %rax), %rax
-	cmp	(%rax), %CHAR_REG
+# ifndef USE_AS_STRCHRNUL
+	cmp (%rax), %CHAR_REG
 	cmovne	%rdx, %rax
 # 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):
-	addq	$VEC_SIZE, %rdi
 
-L(more_4x_vec):
-	/* Check the first 4 * VEC_SIZE.  Only one VEC_SIZE at a time
-	   since data is only aligned to VEC_SIZE.  */
-	vmovdqa	(%rdi), %ymm8
+	/* 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
@@ -137,61 +122,24 @@ L(more_4x_vec):
 	vpor	%ymm1, %ymm2, %ymm1
 	vpmovmskb %ymm1, %eax
 	testl	%eax, %eax
-	jnz	L(first_vec_x3)
-
-	addq	$(VEC_SIZE * 4), %rdi
-
-	/* Align data to 4 * VEC_SIZE.  */
-	movq	%rdi, %rcx
-	andl	$(4 * VEC_SIZE - 1), %ecx
-	andq	$-(4 * VEC_SIZE), %rdi
-
-	.p2align 4
-L(loop_4x_vec):
-	/* Compare 4 * VEC at a time forward.  */
-	vmovdqa	(%rdi), %ymm5
-	vmovdqa	VEC_SIZE(%rdi), %ymm6
-	vmovdqa	(VEC_SIZE * 2)(%rdi), %ymm7
-	vmovdqa	(VEC_SIZE * 3)(%rdi), %ymm8
-
-	VPCMPEQ %ymm5, %ymm0, %ymm1
-	VPCMPEQ %ymm6, %ymm0, %ymm2
-	VPCMPEQ %ymm7, %ymm0, %ymm3
-	VPCMPEQ %ymm8, %ymm0, %ymm4
-
-	VPCMPEQ %ymm5, %ymm9, %ymm5
-	VPCMPEQ %ymm6, %ymm9, %ymm6
-	VPCMPEQ %ymm7, %ymm9, %ymm7
-	VPCMPEQ %ymm8, %ymm9, %ymm8
-
-	vpor	%ymm1, %ymm5, %ymm1
-	vpor	%ymm2, %ymm6, %ymm2
-	vpor	%ymm3, %ymm7, %ymm3
-	vpor	%ymm4, %ymm8, %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
+	jz	L(prep_loop_4x)
 
-	jmp	L(loop_4x_vec)
+	tzcntl	%eax, %eax
+	leaq	(VEC_SIZE * 3)(%rdi, %rax), %rax
+# ifndef USE_AS_STRCHRNUL
+	cmp (%rax), %CHAR_REG
+	cmovne	%rdx, %rax
+# endif
+	VZEROUPPER
+	ret
 
 	.p2align 4
 L(first_vec_x0):
-	/* Found CHAR or the null byte.  */
 	tzcntl	%eax, %eax
-# ifdef USE_AS_STRCHRNUL
+	/* Found CHAR or the null byte.	 */
 	addq	%rdi, %rax
-# else
-	xorl	%edx, %edx
-	leaq	(%rdi, %rax), %rax
-	cmp	(%rax), %CHAR_REG
+# ifndef USE_AS_STRCHRNUL
+	cmp (%rax), %CHAR_REG
 	cmovne	%rdx, %rax
 # endif
 	VZEROUPPER_RETURN
@@ -199,13 +147,9 @@ L(first_vec_x0):
 	.p2align 4
 L(first_vec_x1):
 	tzcntl	%eax, %eax
-# ifdef USE_AS_STRCHRNUL
-	addq	$VEC_SIZE, %rax
-	addq	%rdi, %rax
-# else
-	xorl	%edx, %edx
 	leaq	VEC_SIZE(%rdi, %rax), %rax
-	cmp	(%rax), %CHAR_REG
+# ifndef USE_AS_STRCHRNUL
+	cmp (%rax), %CHAR_REG
 	cmovne	%rdx, %rax
 # endif
 	VZEROUPPER_RETURN
@@ -213,42 +157,97 @@ L(first_vec_x1):
 	.p2align 4
 L(first_vec_x2):
 	tzcntl	%eax, %eax
-# ifdef USE_AS_STRCHRNUL
-	addq	$(VEC_SIZE * 2), %rax
-	addq	%rdi, %rax
-# else
-	xorl	%edx, %edx
+	/* Found CHAR or the null byte.	 */
 	leaq	(VEC_SIZE * 2)(%rdi, %rax), %rax
-	cmp	(%rax), %CHAR_REG
+# ifndef USE_AS_STRCHRNUL
+	cmp (%rax), %CHAR_REG
 	cmovne	%rdx, %rax
 # endif
 	VZEROUPPER_RETURN
 
+L(prep_loop_4x):
+	/* Align data to 4 * VEC_SIZE.	*/
+	andq	$-(VEC_SIZE * 4), %rdi
+
 	.p2align 4
-L(4x_vec_end):
+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
+
+	/* Leaves only CHARS matching esi as 0.	 */
+	vpxor	%ymm5, %ymm0, %ymm1
+	vpxor	%ymm6, %ymm0, %ymm2
+	vpxor	%ymm7, %ymm0, %ymm3
+	vpxor	%ymm8, %ymm0, %ymm4
+
+	VPMINU	%ymm1, %ymm5, %ymm1
+	VPMINU	%ymm2, %ymm6, %ymm2
+	VPMINU	%ymm3, %ymm7, %ymm3
+	VPMINU	%ymm4, %ymm8, %ymm4
+
+	VPMINU	%ymm1, %ymm2, %ymm5
+	VPMINU	%ymm3, %ymm4, %ymm6
+
+	VPMINU	%ymm5, %ymm6, %ymm5
+
+	VPCMPEQ %ymm5, %ymm9, %ymm5
+	vpmovmskb %ymm5, %eax
+
+	addq	$(VEC_SIZE * 4), %rdi
+	testl	%eax, %eax
+	jz  L(loop_4x_vec)
+
+	VPCMPEQ %ymm1, %ymm9, %ymm1
 	vpmovmskb %ymm1, %eax
 	testl	%eax, %eax
 	jnz	L(first_vec_x0)
+
+	VPCMPEQ %ymm2, %ymm9, %ymm2
 	vpmovmskb %ymm2, %eax
 	testl	%eax, %eax
 	jnz	L(first_vec_x1)
-	vpmovmskb %ymm3, %eax
-	testl	%eax, %eax
-	jnz	L(first_vec_x2)
+
+	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
+# endif
+	VZEROUPPER
+	ret
+
+	/* 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
+	vpor	%ymm1, %ymm2, %ymm1
+	vpmovmskb %ymm1, %eax
+	/* Remove the leading bits.	 */
+	sarxl	%ecx, %eax, %eax
 	testl	%eax, %eax
-L(first_vec_x3):
+	jz	L(aligned_more)
 	tzcntl	%eax, %eax
-# ifdef USE_AS_STRCHRNUL
-	addq	$(VEC_SIZE * 3), %rax
+	addq	%rcx, %rdi
 	addq	%rdi, %rax
-# else
-	xorl	%edx, %edx
-	leaq	(VEC_SIZE * 3)(%rdi, %rax), %rax
-	cmp	(%rax), %CHAR_REG
+# ifndef USE_AS_STRCHRNUL
+	cmp (%rax), %CHAR_REG
 	cmovne	%rdx, %rax
 # endif
 	VZEROUPPER_RETURN
 
 END (STRCHR)
-#endif
+# endif
diff --git a/sysdeps/x86_64/multiarch/strchr.c b/sysdeps/x86_64/multiarch/strchr.c
index 7e582f02..5225bd4f 100644
--- a/sysdeps/x86_64/multiarch/strchr.c
+++ b/sysdeps/x86_64/multiarch/strchr.c
@@ -38,11 +38,11 @@ IFUNC_SELECTOR (void)
   const struct cpu_features* cpu_features = __get_cpu_features ();
 
   if (CPU_FEATURE_USABLE_P (cpu_features, AVX2)
+      && CPU_FEATURE_USABLE_P (cpu_features, BMI2)
       && CPU_FEATURES_ARCH_P (cpu_features, AVX_Fast_Unaligned_Load))
     {
       if (CPU_FEATURE_USABLE_P (cpu_features, AVX512VL)
-	  && CPU_FEATURE_USABLE_P (cpu_features, AVX512BW)
-	  && CPU_FEATURE_USABLE_P (cpu_features, BMI2))
+	  && CPU_FEATURE_USABLE_P (cpu_features, AVX512BW))
 	return OPTIMIZE (evex);
 
       if (CPU_FEATURE_USABLE_P (cpu_features, RTM))
-- 
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