x86-64: Optimize bzero

memset with zero as the value to set is by far the majority value (99%+
for Python3 and GCC).

bzero can be slightly more optimized for this case by using a zero-idiom
xor for broadcasting the set value to a register (vector or GPR).

Co-developed-by: Noah Goldstein <goldstein.w.n@gmail.com>

sysdeps/x86_64/memset.S

@@ -35,6 +35,9 @@
   punpcklwd %xmm0, %xmm0; \
   pshufd $0, %xmm0, %xmm0
 
+# define BZERO_ZERO_VEC0() \
+  pxor %xmm0, %xmm0
+
 # define WMEMSET_SET_VEC0_AND_SET_RETURN(d, r) \
   movd d, %xmm0; \
   pshufd $0, %xmm0, %xmm0; \
@@ -53,6 +56,10 @@
 # define MEMSET_SYMBOL(p,s)	memset
 #endif
 
+#ifndef BZERO_SYMBOL
+# define BZERO_SYMBOL(p,s)	__bzero
+#endif
+
 #ifndef WMEMSET_SYMBOL
 # define WMEMSET_CHK_SYMBOL(p,s) p
 # define WMEMSET_SYMBOL(p,s)	__wmemset
@@ -63,6 +70,7 @@
 libc_hidden_builtin_def (memset)
 
 #if IS_IN (libc)
+weak_alias (__bzero, bzero)
 libc_hidden_def (__wmemset)
 weak_alias (__wmemset, wmemset)
 libc_hidden_weak (wmemset)

sysdeps/x86_64/multiarch/Makefile

@@ -1,6 +1,7 @@
 ifeq ($(subdir),string)
 
 sysdep_routines += \
+  bzero \
   memchr-avx2 \
   memchr-avx2-rtm \
   memchr-evex \

sysdeps/x86_64/multiarch/bzero.c

@@ -0,0 +1,106 @@
+/* Multiple versions of bzero.
+   All versions must be listed in ifunc-impl-list.c.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+/* Define multiple versions only for the definition in libc.  */
+#if IS_IN (libc)
+# define __bzero __redirect___bzero
+# include <string.h>
+# undef __bzero
+
+# define SYMBOL_NAME __bzero
+# include <init-arch.h>
+
+extern __typeof (REDIRECT_NAME) OPTIMIZE1 (sse2_unaligned)
+  attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE1 (sse2_unaligned_erms)
+  attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE1 (avx2_unaligned) attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE1 (avx2_unaligned_erms)
+  attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE1 (avx2_unaligned_rtm)
+  attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE1 (avx2_unaligned_erms_rtm)
+  attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE1 (evex_unaligned)
+  attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE1 (evex_unaligned_erms)
+  attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE1 (avx512_unaligned)
+  attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE1 (avx512_unaligned_erms)
+  attribute_hidden;
+
+static inline void *
+IFUNC_SELECTOR (void)
+{
+  const struct cpu_features* cpu_features = __get_cpu_features ();
+
+  if (CPU_FEATURE_USABLE_P (cpu_features, AVX512F)
+      && !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, BMI2))
+	{
+	  if (CPU_FEATURE_USABLE_P (cpu_features, ERMS))
+	    return OPTIMIZE1 (avx512_unaligned_erms);
+
+	  return OPTIMIZE1 (avx512_unaligned);
+	}
+    }
+
+  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, BMI2))
+	{
+	  if (CPU_FEATURE_USABLE_P (cpu_features, ERMS))
+	    return OPTIMIZE1 (evex_unaligned_erms);
+
+	  return OPTIMIZE1 (evex_unaligned);
+	}
+
+      if (CPU_FEATURE_USABLE_P (cpu_features, RTM))
+	{
+	  if (CPU_FEATURE_USABLE_P (cpu_features, ERMS))
+	    return OPTIMIZE1 (avx2_unaligned_erms_rtm);
+
+	  return OPTIMIZE1 (avx2_unaligned_rtm);
+	}
+
+      if (!CPU_FEATURES_ARCH_P (cpu_features, Prefer_No_VZEROUPPER))
+	{
+	  if (CPU_FEATURE_USABLE_P (cpu_features, ERMS))
+	    return OPTIMIZE1 (avx2_unaligned_erms);
+
+	  return OPTIMIZE1 (avx2_unaligned);
+	}
+    }
+
+  if (CPU_FEATURE_USABLE_P (cpu_features, ERMS))
+    return OPTIMIZE1 (sse2_unaligned_erms);
+
+  return OPTIMIZE1 (sse2_unaligned);
+}
+
+libc_ifunc_redirected (__redirect___bzero, __bzero, IFUNC_SELECTOR ());
+
+weak_alias (__bzero, bzero)
+#endif

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

@@ -300,6 +300,48 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			      __memset_avx512_no_vzeroupper)
 	     )
 
+  /* Support sysdeps/x86_64/multiarch/bzero.c.  */
+  IFUNC_IMPL (i, name, bzero,
+	      IFUNC_IMPL_ADD (array, i, bzero, 1,
+			      __bzero_sse2_unaligned)
+	      IFUNC_IMPL_ADD (array, i, bzero, 1,
+			      __bzero_sse2_unaligned_erms)
+	      IFUNC_IMPL_ADD (array, i, bzero,
+			      CPU_FEATURE_USABLE (AVX2),
+			      __bzero_avx2_unaligned)
+	      IFUNC_IMPL_ADD (array, i, bzero,
+			      CPU_FEATURE_USABLE (AVX2),
+			      __bzero_avx2_unaligned_erms)
+	      IFUNC_IMPL_ADD (array, i, bzero,
+			      (CPU_FEATURE_USABLE (AVX2)
+			       && CPU_FEATURE_USABLE (RTM)),
+			      __bzero_avx2_unaligned_rtm)
+	      IFUNC_IMPL_ADD (array, i, bzero,
+			      (CPU_FEATURE_USABLE (AVX2)
+			       && CPU_FEATURE_USABLE (RTM)),
+			      __bzero_avx2_unaligned_erms_rtm)
+	      IFUNC_IMPL_ADD (array, i, bzero,
+			      (CPU_FEATURE_USABLE (AVX512VL)
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
+			      __bzero_evex_unaligned)
+	      IFUNC_IMPL_ADD (array, i, bzero,
+			      (CPU_FEATURE_USABLE (AVX512VL)
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
+			      __bzero_evex_unaligned_erms)
+	      IFUNC_IMPL_ADD (array, i, bzero,
+			      (CPU_FEATURE_USABLE (AVX512VL)
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
+			      __bzero_avx512_unaligned_erms)
+	      IFUNC_IMPL_ADD (array, i, bzero,
+			      (CPU_FEATURE_USABLE (AVX512VL)
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
+			      __bzero_avx512_unaligned)
+	     )
+
   /* Support sysdeps/x86_64/multiarch/rawmemchr.c.  */
   IFUNC_IMPL (i, name, rawmemchr,
 	      IFUNC_IMPL_ADD (array, i, rawmemchr,

sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms-rtm.S

@@ -5,6 +5,7 @@
 
 #define SECTION(p) p##.avx.rtm
 #define MEMSET_SYMBOL(p,s)	p##_avx2_##s##_rtm
+#define BZERO_SYMBOL(p,s)	p##_avx2_##s##_rtm
 #define WMEMSET_SYMBOL(p,s)	p##_avx2_##s##_rtm
 
 #include "memset-avx2-unaligned-erms.S"

sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S

@@ -14,6 +14,9 @@
   vmovd d, %xmm0; \
   movq r, %rax;
 
+# define BZERO_ZERO_VEC0() \
+  vpxor %xmm0, %xmm0, %xmm0
+
 # define WMEMSET_SET_VEC0_AND_SET_RETURN(d, r) \
   MEMSET_SET_VEC0_AND_SET_RETURN(d, r)
 
@@ -29,6 +32,9 @@
 # ifndef MEMSET_SYMBOL
 #  define MEMSET_SYMBOL(p,s)	p##_avx2_##s
 # endif
+# ifndef BZERO_SYMBOL
+#  define BZERO_SYMBOL(p,s)	p##_avx2_##s
+# endif
 # ifndef WMEMSET_SYMBOL
 #  define WMEMSET_SYMBOL(p,s)	p##_avx2_##s
 # endif

sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S

@@ -19,6 +19,9 @@
   vpbroadcastb d, %VEC0; \
   movq r, %rax
 
+# define BZERO_ZERO_VEC0() \
+  vpxorq %XMM0, %XMM0, %XMM0
+
 # define WMEMSET_SET_VEC0_AND_SET_RETURN(d, r) \
   vpbroadcastd d, %VEC0; \
   movq r, %rax

sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S

@@ -19,6 +19,9 @@
   vpbroadcastb d, %VEC0; \
   movq r, %rax
 
+# define BZERO_ZERO_VEC0() \
+  vpxorq %XMM0, %XMM0, %XMM0
+
 # define WMEMSET_SET_VEC0_AND_SET_RETURN(d, r) \
   vpbroadcastd d, %VEC0; \
   movq r, %rax

sysdeps/x86_64/multiarch/memset-sse2-unaligned-erms.S

@@ -22,6 +22,7 @@
 
 #if IS_IN (libc)
 # define MEMSET_SYMBOL(p,s)	p##_sse2_##s
+# define BZERO_SYMBOL(p,s)	MEMSET_SYMBOL (p, s)
 # define WMEMSET_SYMBOL(p,s)	p##_sse2_##s
 
 # ifdef SHARED

sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S

@@ -26,6 +26,10 @@
 
 #include <sysdep.h>
 
+#ifndef BZERO_SYMBOL
+# define BZERO_SYMBOL(p,s)		MEMSET_SYMBOL (p, s)
+#endif
+
 #ifndef MEMSET_CHK_SYMBOL
 # define MEMSET_CHK_SYMBOL(p,s)		MEMSET_SYMBOL(p, s)
 #endif
@@ -87,6 +91,18 @@
 # define XMM_SMALL	0
 #endif
 
+#ifdef USE_LESS_VEC_MASK_STORE
+# define SET_REG64	rcx
+# define SET_REG32	ecx
+# define SET_REG16	cx
+# define SET_REG8	cl
+#else
+# define SET_REG64	rsi
+# define SET_REG32	esi
+# define SET_REG16	si
+# define SET_REG8	sil
+#endif
+
 #define PAGE_SIZE 4096
 
 /* Macro to calculate size of small memset block for aligning
@@ -96,18 +112,6 @@
 
 #ifndef SECTION
 # error SECTION is not defined!
-#endif
-
-	.section SECTION(.text),"ax",@progbits
-#if VEC_SIZE == 16 && IS_IN (libc)
-ENTRY (__bzero)
-	mov	%RDI_LP, %RAX_LP /* Set return value.  */
-	mov	%RSI_LP, %RDX_LP /* Set n.  */
-	xorl	%esi, %esi
-	pxor	%XMM0, %XMM0
-	jmp	L(entry_from_bzero)
-END (__bzero)
-weak_alias (__bzero, bzero)
 #endif
 
 #if IS_IN (libc)
@@ -123,12 +127,37 @@ ENTRY (WMEMSET_SYMBOL (__wmemset, unaligned))
 	WMEMSET_SET_VEC0_AND_SET_RETURN (%esi, %rdi)
 	WMEMSET_VDUP_TO_VEC0_LOW()
 	cmpq	$VEC_SIZE, %rdx
-	jb	L(less_vec_no_vdup)
+	jb	L(less_vec_from_wmemset)
 	WMEMSET_VDUP_TO_VEC0_HIGH()
 	jmp	L(entry_from_wmemset)
 END (WMEMSET_SYMBOL (__wmemset, unaligned))
 #endif
 
+ENTRY (BZERO_SYMBOL(__bzero, unaligned))
+#if VEC_SIZE > 16
+	BZERO_ZERO_VEC0 ()
+#endif
+	mov	%RDI_LP, %RAX_LP
+	mov	%RSI_LP, %RDX_LP
+#ifndef USE_LESS_VEC_MASK_STORE
+	xorl	%esi, %esi
+#endif
+	cmp	$VEC_SIZE, %RDX_LP
+	jb	L(less_vec_no_vdup)
+#ifdef USE_LESS_VEC_MASK_STORE
+	xorl	%esi, %esi
+#endif
+#if VEC_SIZE <= 16
+	BZERO_ZERO_VEC0 ()
+#endif
+	cmp	$(VEC_SIZE * 2), %RDX_LP
+	ja	L(more_2x_vec)
+	/* From VEC and to 2 * VEC.  No branch when size == VEC_SIZE.  */
+	VMOVU	%VEC(0), (%rdi)
+	VMOVU	%VEC(0), (VEC_SIZE * -1)(%rdi, %rdx)
+	VZEROUPPER_RETURN
+END (BZERO_SYMBOL(__bzero, unaligned))
+
 #if defined SHARED && IS_IN (libc)
 ENTRY_CHK (MEMSET_CHK_SYMBOL (__memset_chk, unaligned))
 	cmp	%RDX_LP, %RCX_LP
@@ -142,7 +171,6 @@ ENTRY (MEMSET_SYMBOL (__memset, unaligned))
 	/* Clear the upper 32 bits.  */
 	mov	%edx, %edx
 # endif
-L(entry_from_bzero):
 	cmpq	$VEC_SIZE, %rdx
 	jb	L(less_vec)
 	MEMSET_VDUP_TO_VEC0_HIGH()
@@ -187,6 +215,31 @@ END (__memset_erms)
 END (MEMSET_SYMBOL (__memset, erms))
 # endif
 
+ENTRY_P2ALIGN (BZERO_SYMBOL(__bzero, unaligned_erms), 6)
+# if VEC_SIZE > 16
+	BZERO_ZERO_VEC0 ()
+# endif
+	mov	%RDI_LP, %RAX_LP
+	mov	%RSI_LP, %RDX_LP
+# ifndef USE_LESS_VEC_MASK_STORE
+	xorl	%esi, %esi
+# endif
+	cmp	$VEC_SIZE, %RDX_LP
+	jb	L(less_vec_no_vdup)
+# ifdef USE_LESS_VEC_MASK_STORE
+	xorl	%esi, %esi
+# endif
+# if VEC_SIZE <= 16
+	BZERO_ZERO_VEC0 ()
+# endif
+	cmp	$(VEC_SIZE * 2), %RDX_LP
+	ja	L(stosb_more_2x_vec)
+	/* From VEC and to 2 * VEC.  No branch when size == VEC_SIZE.  */
+	VMOVU	%VEC(0), (%rdi)
+	VMOVU	%VEC(0), (VEC_SIZE * -1)(%rdi, %rdx)
+	VZEROUPPER_RETURN
+END (BZERO_SYMBOL(__bzero, unaligned_erms))
+
 # if defined SHARED && IS_IN (libc)
 ENTRY_CHK (MEMSET_CHK_SYMBOL (__memset_chk, unaligned_erms))
 	cmp	%RDX_LP, %RCX_LP
@@ -229,6 +282,7 @@ L(last_2x_vec):
 	.p2align 4,, 10
 L(less_vec):
 L(less_vec_no_vdup):
+L(less_vec_from_wmemset):
 	/* Less than 1 VEC.  */
 # if VEC_SIZE != 16 && VEC_SIZE != 32 && VEC_SIZE != 64
 #  error Unsupported VEC_SIZE!
@@ -374,8 +428,11 @@ L(less_vec):
 	/* Broadcast esi to partial register (i.e VEC_SIZE == 32 broadcast to
 	   xmm). This is only does anything for AVX2.  */
 	MEMSET_VDUP_TO_VEC0_LOW ()
+L(less_vec_from_wmemset):
+#if VEC_SIZE > 16
 L(less_vec_no_vdup):
 #endif
+#endif
 L(cross_page):
 #if VEC_SIZE > 32
 	cmpl	$32, %edx
@@ -386,7 +443,10 @@ L(cross_page):
 	jge	L(between_16_31)
 #endif
 #ifndef USE_XMM_LESS_VEC
-	MOVQ	%XMM0, %rcx
+	MOVQ	%XMM0, %SET_REG64
+#endif
+#if VEC_SIZE <= 16
+L(less_vec_no_vdup):
 #endif
 	cmpl	$8, %edx
 	jge	L(between_8_15)
@@ -395,7 +455,7 @@ L(cross_page):
 	cmpl	$1, %edx
 	jg	L(between_2_3)
 	jl	L(between_0_0)
-	movb	%sil, (%LESS_VEC_REG)
+	movb	%SET_REG8, (%LESS_VEC_REG)
 L(between_0_0):
 	ret
 
@@ -428,8 +488,8 @@ L(between_8_15):
 	MOVQ	%XMM0, (%rdi)
 	MOVQ	%XMM0, -8(%rdi, %rdx)
 #else
-	movq	%rcx, (%LESS_VEC_REG)
+	movq	%SET_REG64, (%LESS_VEC_REG)
-	movq	%rcx, -8(%LESS_VEC_REG, %rdx)
+	movq	%SET_REG64, -8(%LESS_VEC_REG, %rdx)
 #endif
 	ret
 
@@ -442,8 +502,8 @@ L(between_4_7):
 	MOVD	%XMM0, (%rdi)
 	MOVD	%XMM0, -4(%rdi, %rdx)
 #else
-	movl	%ecx, (%LESS_VEC_REG)
+	movl	%SET_REG32, (%LESS_VEC_REG)
-	movl	%ecx, -4(%LESS_VEC_REG, %rdx)
+	movl	%SET_REG32, -4(%LESS_VEC_REG, %rdx)
 #endif
 	ret
 
@@ -452,12 +512,12 @@ L(between_4_7):
 L(between_2_3):
 	/* From 2 to 3.  No branch when size == 2.  */
 #ifdef USE_XMM_LESS_VEC
-	movb	%sil, (%rdi)
+	movb	%SET_REG8, (%rdi)
-	movb	%sil, 1(%rdi)
+	movb	%SET_REG8, 1(%rdi)
-	movb	%sil, -1(%rdi, %rdx)
+	movb	%SET_REG8, -1(%rdi, %rdx)
 #else
-	movw	%cx, (%LESS_VEC_REG)
+	movw	%SET_REG16, (%LESS_VEC_REG)
-	movb	%sil, -1(%LESS_VEC_REG, %rdx)
+	movb	%SET_REG8, -1(%LESS_VEC_REG, %rdx)
 #endif
 	ret
 END (MEMSET_SYMBOL (__memset, unaligned_erms))