From f53790272ce7bdc5ecd14b45f65d0464d2a61a3a Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n@gmail.com>
Date: Mon, 19 Apr 2021 17:48:10 -0400
Subject: [PATCH] x86: Optimize less_vec evex and avx512
 memset-vec-unaligned-erms.S
Content-type: text/plain; charset=UTF-8

No bug. This commit adds optimized cased for less_vec memset case that
uses the avx512vl/avx512bw mask store avoiding the excessive
branches. test-memset and test-wmemset are passing.

Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
---
 sysdeps/x86_64/multiarch/ifunc-impl-list.c    | 40 ++++++++++-----
 sysdeps/x86_64/multiarch/ifunc-memset.h       |  6 ++-
 .../multiarch/memset-avx512-unaligned-erms.S  |  2 +-
 .../multiarch/memset-evex-unaligned-erms.S    |  2 +-
 .../multiarch/memset-vec-unaligned-erms.S     | 51 +++++++++++++++----
 5 files changed, 74 insertions(+), 27 deletions(-)

diff --git a/sysdeps/x86_64/multiarch/ifunc-impl-list.c b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
index 85b8863a..d59d65f8 100644
--- a/sysdeps/x86_64/multiarch/ifunc-impl-list.c
+++ b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
@@ -204,19 +204,23 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			      __memset_chk_avx2_unaligned_erms_rtm)
 	      IFUNC_IMPL_ADD (array, i, __memset_chk,
 			      (CPU_FEATURE_USABLE (AVX512VL)
-			       && CPU_FEATURE_USABLE (AVX512BW)),
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
 			      __memset_chk_evex_unaligned)
 	      IFUNC_IMPL_ADD (array, i, __memset_chk,
 			      (CPU_FEATURE_USABLE (AVX512VL)
-			       && CPU_FEATURE_USABLE (AVX512BW)),
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
 			      __memset_chk_evex_unaligned_erms)
 	      IFUNC_IMPL_ADD (array, i, __memset_chk,
 			      (CPU_FEATURE_USABLE (AVX512VL)
-			       && CPU_FEATURE_USABLE (AVX512BW)),
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
 			      __memset_chk_avx512_unaligned_erms)
 	      IFUNC_IMPL_ADD (array, i, __memset_chk,
 			      (CPU_FEATURE_USABLE (AVX512VL)
-			       && CPU_FEATURE_USABLE (AVX512BW)),
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
 			      __memset_chk_avx512_unaligned)
 	      IFUNC_IMPL_ADD (array, i, __memset_chk,
 			      CPU_FEATURE_USABLE (AVX512F),
@@ -247,19 +251,23 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			      __memset_avx2_unaligned_erms_rtm)
 	      IFUNC_IMPL_ADD (array, i, memset,
 			      (CPU_FEATURE_USABLE (AVX512VL)
-			       && CPU_FEATURE_USABLE (AVX512BW)),
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
 			      __memset_evex_unaligned)
 	      IFUNC_IMPL_ADD (array, i, memset,
 			      (CPU_FEATURE_USABLE (AVX512VL)
-			       && CPU_FEATURE_USABLE (AVX512BW)),
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
 			      __memset_evex_unaligned_erms)
 	      IFUNC_IMPL_ADD (array, i, memset,
 			      (CPU_FEATURE_USABLE (AVX512VL)
-			       && CPU_FEATURE_USABLE (AVX512BW)),
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
 			      __memset_avx512_unaligned_erms)
 	      IFUNC_IMPL_ADD (array, i, memset,
 			      (CPU_FEATURE_USABLE (AVX512VL)
-			       && CPU_FEATURE_USABLE (AVX512BW)),
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
 			      __memset_avx512_unaligned)
 	      IFUNC_IMPL_ADD (array, i, memset,
 			      CPU_FEATURE_USABLE (AVX512F),
@@ -739,10 +747,14 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			       && CPU_FEATURE_USABLE (RTM)),
 			      __wmemset_avx2_unaligned_rtm)
 	      IFUNC_IMPL_ADD (array, i, wmemset,
-			      CPU_FEATURE_USABLE (AVX512VL),
+			      (CPU_FEATURE_USABLE (AVX512VL)
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
 			      __wmemset_evex_unaligned)
 	      IFUNC_IMPL_ADD (array, i, wmemset,
-			      CPU_FEATURE_USABLE (AVX512VL),
+			      (CPU_FEATURE_USABLE (AVX512VL)
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
 			      __wmemset_avx512_unaligned))
 
 #ifdef SHARED
@@ -946,10 +958,14 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			      CPU_FEATURE_USABLE (AVX2),
 			      __wmemset_chk_avx2_unaligned)
 	      IFUNC_IMPL_ADD (array, i, __wmemset_chk,
-			      CPU_FEATURE_USABLE (AVX512VL),
+			      (CPU_FEATURE_USABLE (AVX512VL)
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
 			      __wmemset_chk_evex_unaligned)
 	      IFUNC_IMPL_ADD (array, i, __wmemset_chk,
-			      CPU_FEATURE_USABLE (AVX512F),
+			      (CPU_FEATURE_USABLE (AVX512VL)
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
 			      __wmemset_chk_avx512_unaligned))
 #endif
 
diff --git a/sysdeps/x86_64/multiarch/ifunc-memset.h b/sysdeps/x86_64/multiarch/ifunc-memset.h
index 19795938..100e3707 100644
--- a/sysdeps/x86_64/multiarch/ifunc-memset.h
+++ b/sysdeps/x86_64/multiarch/ifunc-memset.h
@@ -54,7 +54,8 @@ IFUNC_SELECTOR (void)
       && !CPU_FEATURES_ARCH_P (cpu_features, Prefer_No_AVX512))
     {
       if (CPU_FEATURE_USABLE_P (cpu_features, AVX512VL)
-	  && CPU_FEATURE_USABLE_P (cpu_features, AVX512BW))
+          && CPU_FEATURE_USABLE_P (cpu_features, AVX512BW)
+          && CPU_FEATURE_USABLE_P (cpu_features, BMI2))
 	{
 	  if (CPU_FEATURE_USABLE_P (cpu_features, ERMS))
 	    return OPTIMIZE (avx512_unaligned_erms);
@@ -68,7 +69,8 @@ IFUNC_SELECTOR (void)
   if (CPU_FEATURE_USABLE_P (cpu_features, AVX2))
     {
       if (CPU_FEATURE_USABLE_P (cpu_features, AVX512VL)
-	  && CPU_FEATURE_USABLE_P (cpu_features, AVX512BW))
+          && CPU_FEATURE_USABLE_P (cpu_features, AVX512BW)
+          && CPU_FEATURE_USABLE_P (cpu_features, BMI2))
 	{
 	  if (CPU_FEATURE_USABLE_P (cpu_features, ERMS))
 	    return OPTIMIZE (evex_unaligned_erms);
diff --git a/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S
index 22e7b187..8ad842fc 100644
--- a/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S
+++ b/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S
@@ -19,6 +19,6 @@
 # define SECTION(p)		p##.evex512
 # define MEMSET_SYMBOL(p,s)	p##_avx512_##s
 # define WMEMSET_SYMBOL(p,s)	p##_avx512_##s
-
+# define USE_LESS_VEC_MASK_STORE	1
 # include "memset-vec-unaligned-erms.S"
 #endif
diff --git a/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S
index ae0a4d6e..640f0929 100644
--- a/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S
+++ b/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S
@@ -19,6 +19,6 @@
 # define SECTION(p)		p##.evex
 # define MEMSET_SYMBOL(p,s)	p##_evex_##s
 # define WMEMSET_SYMBOL(p,s)	p##_evex_##s
-
+# define USE_LESS_VEC_MASK_STORE	1
 # include "memset-vec-unaligned-erms.S"
 #endif
diff --git a/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
index bae5cba4..f877ac9d 100644
--- a/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
+++ b/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
@@ -63,6 +63,8 @@
 # endif
 #endif
 
+#define PAGE_SIZE 4096
+
 #ifndef SECTION
 # error SECTION is not defined!
 #endif
@@ -213,11 +215,38 @@ L(loop):
 	cmpq	%rcx, %rdx
 	jne	L(loop)
 	VZEROUPPER_SHORT_RETURN
+
+	.p2align 4
 L(less_vec):
 	/* Less than 1 VEC.  */
 # if VEC_SIZE != 16 && VEC_SIZE != 32 && VEC_SIZE != 64
 #  error Unsupported VEC_SIZE!
 # endif
+# ifdef USE_LESS_VEC_MASK_STORE
+	/* Clear high bits from edi. Only keeping bits relevant to page
+	   cross check. Note that we are using rax which is set in
+	   MEMSET_VDUP_TO_VEC0_AND_SET_RETURN as ptr from here on out.
+	 */
+	andl	$(PAGE_SIZE - 1), %edi
+	/* Check if VEC_SIZE store cross page. Mask stores suffer serious
+	   performance degradation when it has to fault supress.  */
+	cmpl	$(PAGE_SIZE - VEC_SIZE), %edi
+	ja	L(cross_page)
+# if VEC_SIZE > 32
+	movq	$-1, %rcx
+	bzhiq	%rdx, %rcx, %rcx
+	kmovq	%rcx, %k1
+# else
+	movl	$-1, %ecx
+	bzhil	%edx, %ecx, %ecx
+	kmovd	%ecx, %k1
+# endif
+	vmovdqu8	%VEC(0), (%rax) {%k1}
+	VZEROUPPER_RETURN
+
+	.p2align 4
+L(cross_page):
+# endif
 # if VEC_SIZE > 32
 	cmpb	$32, %dl
 	jae	L(between_32_63)
@@ -234,36 +263,36 @@ L(less_vec):
 	cmpb	$1, %dl
 	ja	L(between_2_3)
 	jb	1f
-	movb	%cl, (%rdi)
+	movb	%cl, (%rax)
 1:
 	VZEROUPPER_RETURN
 # if VEC_SIZE > 32
 	/* From 32 to 63.  No branch when size == 32.  */
 L(between_32_63):
-	VMOVU	%YMM0, -32(%rdi,%rdx)
-	VMOVU	%YMM0, (%rdi)
+	VMOVU	%YMM0, -32(%rax,%rdx)
+	VMOVU	%YMM0, (%rax)
 	VZEROUPPER_RETURN
 # endif
 # if VEC_SIZE > 16
 	/* From 16 to 31.  No branch when size == 16.  */
 L(between_16_31):
-	VMOVU	%XMM0, -16(%rdi,%rdx)
-	VMOVU	%XMM0, (%rdi)
+	VMOVU	%XMM0, -16(%rax,%rdx)
+	VMOVU	%XMM0, (%rax)
 	VZEROUPPER_RETURN
 # endif
 	/* From 8 to 15.  No branch when size == 8.  */
 L(between_8_15):
-	movq	%rcx, -8(%rdi,%rdx)
-	movq	%rcx, (%rdi)
+	movq	%rcx, -8(%rax,%rdx)
+	movq	%rcx, (%rax)
 	VZEROUPPER_RETURN
 L(between_4_7):
 	/* From 4 to 7.  No branch when size == 4.  */
-	movl	%ecx, -4(%rdi,%rdx)
-	movl	%ecx, (%rdi)
+	movl	%ecx, -4(%rax,%rdx)
+	movl	%ecx, (%rax)
 	VZEROUPPER_RETURN
 L(between_2_3):
 	/* From 2 to 3.  No branch when size == 2.  */
-	movw	%cx, -2(%rdi,%rdx)
-	movw	%cx, (%rdi)
+	movw	%cx, -2(%rax,%rdx)
+	movw	%cx, (%rax)
 	VZEROUPPER_RETURN
 END (MEMSET_SYMBOL (__memset, unaligned_erms))
-- 
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