x86: Add EVEX optimized memchr family not safe for RTM

No bug.

This commit adds a new implementation for EVEX memchr that is not safe
for RTM because it uses vzeroupper. The benefit is that by using
ymm0-ymm15 it can use vpcmpeq and vpternlogd in the 4x loop which is
faster than the RTM safe version which cannot use vpcmpeq because
there is no EVEX encoding for the instruction. All parts of the
implementation aside from the 4x loop are the same for the two
versions and the optimization is only relevant for large sizes.

Tigerlake:
size  , algn  , Pos   , Cur T , New T , Win     , Dif
512   , 6     , 192   , 9.2   , 9.04  , no-RTM  , 0.16
512   , 7     , 224   , 9.19  , 8.98  , no-RTM  , 0.21
2048  , 0     , 256   , 10.74 , 10.54 , no-RTM  , 0.2
2048  , 0     , 512   , 14.81 , 14.87 , RTM     , 0.06
2048  , 0     , 1024  , 22.97 , 22.57 , no-RTM  , 0.4
2048  , 0     , 2048  , 37.49 , 34.51 , no-RTM  , 2.98   <--

Icelake:
size  , algn  , Pos   , Cur T , New T , Win     , Dif
512   , 6     , 192   , 7.6   , 7.3   , no-RTM  , 0.3
512   , 7     , 224   , 7.63  , 7.27  , no-RTM  , 0.36
2048  , 0     , 256   , 8.48  , 8.38  , no-RTM  , 0.1
2048  , 0     , 512   , 11.57 , 11.42 , no-RTM  , 0.15
2048  , 0     , 1024  , 17.92 , 17.38 , no-RTM  , 0.54
2048  , 0     , 2048  , 30.37 , 27.34 , no-RTM  , 3.03   <--

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

Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

sysdeps/x86_64/multiarch/Makefile

@@ -77,7 +77,9 @@ sysdep_routines += strncat-c stpncpy-c strncpy-c \
 		   strncmp-evex \
 		   strncpy-evex \
 		   strnlen-evex \
-		   strrchr-evex
+		   strrchr-evex \
+		   memchr-evex-rtm \
+		   rawmemchr-evex-rtm
 CFLAGS-varshift.c += -msse4
 CFLAGS-strcspn-c.c += -msse4
 CFLAGS-strpbrk-c.c += -msse4
@@ -110,7 +112,8 @@ sysdep_routines += wmemcmp-sse4 wmemcmp-ssse3 wmemcmp-c \
 		   wcsnlen-evex \
 		   wcsrchr-evex \
 		   wmemchr-evex \
-		   wmemcmp-evex-movbe
+		   wmemcmp-evex-movbe \
+		   wmemchr-evex-rtm
 endif
 
 ifeq ($(subdir),debug)

sysdeps/x86_64/multiarch/ifunc-evex.h

@@ -0,0 +1,55 @@
+/* Common definition for ifunc selection optimized with EVEX.
+   All versions must be listed in ifunc-impl-list.c.
+   Copyright (C) 2017-2021 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/>.  */
+
+#include <init-arch.h>
+
+extern __typeof (REDIRECT_NAME) OPTIMIZE (sse2) attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE (avx2) attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE (avx2_rtm) attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE (evex) attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE (evex_rtm) attribute_hidden;
+
+
+static inline void *
+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))
+	{
+	  if (CPU_FEATURE_USABLE_P (cpu_features, RTM))
+	    return OPTIMIZE (evex_rtm);
+
+	  return OPTIMIZE (evex);
+	}
+
+      if (CPU_FEATURE_USABLE_P (cpu_features, RTM))
+	return OPTIMIZE (avx2_rtm);
+
+      if (!CPU_FEATURES_ARCH_P (cpu_features, Prefer_No_VZEROUPPER))
+	return OPTIMIZE (avx2);
+    }
+
+  return OPTIMIZE (sse2);
+}

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

@@ -52,6 +52,11 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			       && CPU_FEATURE_USABLE (AVX512BW)
 			       && CPU_FEATURE_USABLE (BMI2)),
 			      __memchr_evex)
+	      IFUNC_IMPL_ADD (array, i, memchr,
+			      (CPU_FEATURE_USABLE (AVX512VL)
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
+			      __memchr_evex_rtm)
 	      IFUNC_IMPL_ADD (array, i, memchr, 1, __memchr_sse2))
 
   /* Support sysdeps/x86_64/multiarch/memcmp.c.  */
@@ -288,6 +293,11 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			       && CPU_FEATURE_USABLE (AVX512BW)
 			       && CPU_FEATURE_USABLE (BMI2)),
 			      __rawmemchr_evex)
+	      IFUNC_IMPL_ADD (array, i, rawmemchr,
+			      (CPU_FEATURE_USABLE (AVX512VL)
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
+			      __rawmemchr_evex_rtm)
 	      IFUNC_IMPL_ADD (array, i, rawmemchr, 1, __rawmemchr_sse2))
 
   /* Support sysdeps/x86_64/multiarch/strlen.c.  */
@@ -708,6 +718,11 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 			       && CPU_FEATURE_USABLE (AVX512BW)
 			       && CPU_FEATURE_USABLE (BMI2)),
 			      __wmemchr_evex)
+	      IFUNC_IMPL_ADD (array, i, wmemchr,
+			      (CPU_FEATURE_USABLE (AVX512VL)
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)),
+			      __wmemchr_evex_rtm)
 	      IFUNC_IMPL_ADD (array, i, wmemchr, 1, __wmemchr_sse2))
 
   /* Support sysdeps/x86_64/multiarch/wmemcmp.c.  */

sysdeps/x86_64/multiarch/memchr-evex-rtm.S

@@ -0,0 +1,8 @@
+#ifndef MEMCHR
+# define MEMCHR __memchr_evex_rtm
+#endif
+
+#define USE_IN_RTM 1
+#define SECTION(p) p##.evex.rtm
+
+#include "memchr-evex.S"

sysdeps/x86_64/multiarch/memchr-evex.S

@@ -38,10 +38,32 @@
 #  define CHAR_SIZE	1
 # endif
 
+	/* In the 4x loop the RTM and non-RTM versions have data pointer
+	   off by VEC_SIZE * 4 with RTM version being VEC_SIZE * 4 greater.
+	   This is represented by BASE_OFFSET. As well because the RTM
+	   version uses vpcmp which stores a bit per element compared where
+	   the non-RTM version uses vpcmpeq which stores a bit per byte
+	   compared RET_SCALE of CHAR_SIZE is only relevant for the RTM
+	   version.  */
+# ifdef USE_IN_RTM
+#  define VZEROUPPER
+#  define BASE_OFFSET	(VEC_SIZE * 4)
+#  define RET_SCALE	CHAR_SIZE
+# else
+#  define VZEROUPPER	vzeroupper
+#  define BASE_OFFSET	0
+#  define RET_SCALE	1
+# endif
+
+	/* In the return from 4x loop memchr and rawmemchr versions have
+	   data pointers off by VEC_SIZE * 4 with memchr version being
+	   VEC_SIZE * 4 greater.  */
 # ifdef USE_AS_RAWMEMCHR
+#  define RET_OFFSET	(BASE_OFFSET - (VEC_SIZE * 4))
 #  define RAW_PTR_REG	rcx
 #  define ALGN_PTR_REG	rdi
 # else
+#  define RET_OFFSET	BASE_OFFSET
 #  define RAW_PTR_REG	rdi
 #  define ALGN_PTR_REG	rcx
 # endif
@@ -57,11 +79,15 @@
 # define YMM5		ymm21
 # define YMM6		ymm22
 
+# ifndef SECTION
+#  define SECTION(p)	p##.evex
+# endif
+
 # define VEC_SIZE 32
 # define CHAR_PER_VEC (VEC_SIZE / CHAR_SIZE)
 # define PAGE_SIZE 4096
 
-	.section .text.evex,"ax",@progbits
+	.section SECTION(.text),"ax",@progbits
 ENTRY (MEMCHR)
 # ifndef USE_AS_RAWMEMCHR
 	/* Check for zero length.  */
@@ -237,14 +263,15 @@ L(cross_page_continue):
 	/* Check if at last CHAR_PER_VEC * 4 length.  */
 	subq	$(CHAR_PER_VEC * 4), %rdx
 	jbe	L(last_4x_vec_or_less_cmpeq)
-	addq	$VEC_SIZE, %rdi
+	/* +VEC_SIZE if USE_IN_RTM otherwise +VEC_SIZE * 5.  */
+	addq	$(VEC_SIZE + (VEC_SIZE * 4 - BASE_OFFSET)), %rdi
 
 	/* Align data to VEC_SIZE * 4 for the loop and readjust length.
 	 */
 #  ifdef USE_AS_WMEMCHR
 	movl	%edi, %ecx
 	andq	$-(4 * VEC_SIZE), %rdi
-	andl	$(VEC_SIZE * 4 - 1), %ecx
+	subl	%edi, %ecx
 	/* NB: Divide bytes by 4 to get the wchar_t count.  */
 	sarl	$2, %ecx
 	addq	%rcx, %rdx
@@ -254,15 +281,28 @@ L(cross_page_continue):
 	subq	%rdi, %rdx
 #  endif
 # else
-	addq	$VEC_SIZE, %rdi
+	addq	$(VEC_SIZE + (VEC_SIZE * 4 - BASE_OFFSET)), %rdi
 	andq	$-(4 * VEC_SIZE), %rdi
 # endif
-
+# ifdef USE_IN_RTM
 	vpxorq	%XMMZERO, %XMMZERO, %XMMZERO
+# else
+	/* copy ymmmatch to ymm0 so we can use vpcmpeq which is not
+	   encodable with EVEX registers (ymm16-ymm31).  */
+	vmovdqa64 %YMMMATCH, %ymm0
+# endif
 
 	/* Compare 4 * VEC at a time forward.  */
 	.p2align 4
 L(loop_4x_vec):
+	/* Two versions of the loop. One that does not require
+	   vzeroupper by not using ymm0-ymm15 and another does that require
+	   vzeroupper because it uses ymm0-ymm15. The reason why ymm0-ymm15
+	   is used at all is because there is no EVEX encoding vpcmpeq and
+	   with vpcmpeq this loop can be performed more efficiently. The
+	   non-vzeroupper version is safe for RTM while the vzeroupper
+	   version should be prefered if RTM are not supported.  */
+# ifdef USE_IN_RTM
 	/* It would be possible to save some instructions using 4x VPCMP
 	   but bottleneck on port 5 makes it not woth it.  */
 	VPCMP	$4, (VEC_SIZE * 4)(%rdi), %YMMMATCH, %k1
@@ -273,12 +313,55 @@ L(loop_4x_vec):
 	/* Reduce VEC2 / VEC3 with min and VEC1 with zero mask.  */
 	VPMINU	%YMM2, %YMM3, %YMM3{%k1}{z}
 	VPCMP	$0, %YMM3, %YMMZERO, %k2
+# else
+	/* Since vptern can only take 3x vectors fastest to do 1 vec
+	   seperately with EVEX vpcmp.  */
+#  ifdef USE_AS_WMEMCHR
+	/* vptern can only accept masks for epi32/epi64 so can only save
+	   instruction using not equals mask on vptern with wmemchr.  */
+	VPCMP	$4, (%rdi), %YMMMATCH, %k1
+#  else
+	VPCMP	$0, (%rdi), %YMMMATCH, %k1
+#  endif
+	/* Compare 3x with vpcmpeq and or them all together with vptern.
+	 */
+	VPCMPEQ	VEC_SIZE(%rdi), %ymm0, %ymm2
+	VPCMPEQ	(VEC_SIZE * 2)(%rdi), %ymm0, %ymm3
+	VPCMPEQ	(VEC_SIZE * 3)(%rdi), %ymm0, %ymm4
+#  ifdef USE_AS_WMEMCHR
+	/* This takes the not of or between ymm2, ymm3, ymm4 as well as
+	   combines result from VEC0 with zero mask.  */
+	vpternlogd $1, %ymm2, %ymm3, %ymm4{%k1}{z}
+	vpmovmskb %ymm4, %ecx
+#  else
+	/* 254 is mask for oring ymm2, ymm3, ymm4 into ymm4.  */
+	vpternlogd $254, %ymm2, %ymm3, %ymm4
+	vpmovmskb %ymm4, %ecx
+	kmovd	%k1, %eax
+#  endif
+# endif
+
 # ifdef USE_AS_RAWMEMCHR
 	subq	$-(VEC_SIZE * 4), %rdi
+# endif
+# ifdef USE_IN_RTM
 	kortestd %k2, %k3
+# else
+#  ifdef USE_AS_WMEMCHR
+	/* ecx contains not of matches. All 1s means no matches. incl will
+	   overflow and set zeroflag if that is the case.  */
+	incl	%ecx
+#  else
+	/* If either VEC1 (eax) or VEC2-VEC4 (ecx) are not zero. Adding
+	   to ecx is not an issue because if eax is non-zero it will be
+	   used for returning the match. If it is zero the add does
+	   nothing.  */
+	addq	%rax, %rcx
+#  endif
+# endif
+# ifdef USE_AS_RAWMEMCHR
 	jz	L(loop_4x_vec)
 # else
-	kortestd %k2, %k3
 	jnz	L(loop_4x_vec_end)
 
 	subq	$-(VEC_SIZE * 4), %rdi
@@ -288,10 +371,11 @@ L(loop_4x_vec):
 
 	/* Fall through into less than 4 remaining vectors of length case.
 	 */
-	VPCMP	$0, (VEC_SIZE * 4)(%rdi), %YMMMATCH, %k0
+	VPCMP	$0, BASE_OFFSET(%rdi), %YMMMATCH, %k0
+	addq	$(BASE_OFFSET - VEC_SIZE), %rdi
 	kmovd	%k0, %eax
-	addq	$(VEC_SIZE * 3), %rdi
+	VZEROUPPER
-	.p2align 4
+
 L(last_4x_vec_or_less):
 	/* Check if first VEC contained match.  */
 	testl	%eax, %eax
@@ -338,73 +422,78 @@ L(loop_4x_vec_end):
 	/* rawmemchr will fall through into this if match was found in
 	   loop.  */
 
+# if defined USE_IN_RTM || defined USE_AS_WMEMCHR
 	/* k1 has not of matches with VEC1.  */
 	kmovd	%k1, %eax
-# ifdef USE_AS_WMEMCHR
+#  ifdef USE_AS_WMEMCHR
 	subl	$((1 << CHAR_PER_VEC) - 1), %eax
-# else
+#  else
 	incl	%eax
+#  endif
+# else
+	/* eax already has matches for VEC1.  */
+	testl	%eax, %eax
 # endif
 	jnz	L(last_vec_x1_return)
 
+# ifdef USE_IN_RTM
 	VPCMP	$0, %YMM2, %YMMZERO, %k0
 	kmovd	%k0, %eax
+# else
+	vpmovmskb %ymm2, %eax
+# endif
 	testl	%eax, %eax
 	jnz	L(last_vec_x2_return)
 
+# ifdef USE_IN_RTM
 	kmovd	%k2, %eax
 	testl	%eax, %eax
 	jnz	L(last_vec_x3_return)
 
 	kmovd	%k3, %eax
 	tzcntl	%eax, %eax
-# ifdef USE_AS_RAWMEMCHR
+	leaq	(VEC_SIZE * 3 + RET_OFFSET)(%rdi, %rax, CHAR_SIZE), %rax
-	leaq	(VEC_SIZE * 3)(%rdi, %rax, CHAR_SIZE), %rax
 # else
-	leaq	(VEC_SIZE * 7)(%rdi, %rax, CHAR_SIZE), %rax
+	vpmovmskb %ymm3, %eax
+	/* Combine matches in VEC3 (eax) with matches in VEC4 (ecx).  */
+	salq	$VEC_SIZE, %rcx
+	orq	%rcx, %rax
+	tzcntq	%rax, %rax
+	leaq	(VEC_SIZE * 2 + RET_OFFSET)(%rdi, %rax), %rax
+	VZEROUPPER
 # endif
 	ret
 
 	.p2align 4
 L(last_vec_x1_return):
 	tzcntl	%eax, %eax
-# ifdef USE_AS_RAWMEMCHR
+# if defined USE_AS_WMEMCHR || RET_OFFSET != 0
-#  ifdef USE_AS_WMEMCHR
 	/* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count.  */
-	leaq	(%rdi, %rax, CHAR_SIZE), %rax
+	leaq	RET_OFFSET(%rdi, %rax, CHAR_SIZE), %rax
-#  else
-	addq	%rdi, %rax
-#  endif
 # else
-	/* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count.  */
+	addq	%rdi, %rax
-	leaq	(VEC_SIZE * 4)(%rdi, %rax, CHAR_SIZE), %rax
 # endif
+	VZEROUPPER
 	ret
 
 	.p2align 4
 L(last_vec_x2_return):
 	tzcntl	%eax, %eax
-# ifdef USE_AS_RAWMEMCHR
+	/* NB: Multiply bytes by RET_SCALE to get the wchar_t count
-	/* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count.  */
+	   if relevant (RET_SCALE = CHAR_SIZE if USE_AS_WMEMCHAR and
-	leaq	VEC_SIZE(%rdi, %rax, CHAR_SIZE), %rax
+	   USE_IN_RTM are both defined. Otherwise RET_SCALE = 1.  */
-# else
+	leaq	(VEC_SIZE + RET_OFFSET)(%rdi, %rax, RET_SCALE), %rax
-	/* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count.  */
+	VZEROUPPER
-	leaq	(VEC_SIZE * 5)(%rdi, %rax, CHAR_SIZE), %rax
-# endif
 	ret
 
+# ifdef USE_IN_RTM
 	.p2align 4
 L(last_vec_x3_return):
 	tzcntl	%eax, %eax
-# ifdef USE_AS_RAWMEMCHR
 	/* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count.  */
-	leaq	(VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %rax
+	leaq	(VEC_SIZE * 2 + RET_OFFSET)(%rdi, %rax, CHAR_SIZE), %rax
-# else
-	/* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count.  */
-	leaq	(VEC_SIZE * 6)(%rdi, %rax, CHAR_SIZE), %rax
-# endif
 	ret
-
+# endif
 
 # ifndef USE_AS_RAWMEMCHR
 L(last_4x_vec_or_less_cmpeq):

sysdeps/x86_64/multiarch/memchr.c

@@ -24,7 +24,7 @@
 # undef memchr
 
 # define SYMBOL_NAME memchr
-# include "ifunc-avx2.h"
+# include "ifunc-evex.h"
 
 libc_ifunc_redirected (__redirect_memchr, memchr, IFUNC_SELECTOR ());
 strong_alias (memchr, __memchr)

sysdeps/x86_64/multiarch/rawmemchr-evex-rtm.S

@@ -0,0 +1,3 @@
+#define MEMCHR __rawmemchr_evex_rtm
+#define USE_AS_RAWMEMCHR 1
+#include "memchr-evex-rtm.S"

sysdeps/x86_64/multiarch/rawmemchr.c

@@ -26,7 +26,7 @@
 # undef __rawmemchr
 
 # define SYMBOL_NAME rawmemchr
-# include "ifunc-avx2.h"
+# include "ifunc-evex.h"
 
 libc_ifunc_redirected (__redirect_rawmemchr, __rawmemchr,
 		       IFUNC_SELECTOR ());

sysdeps/x86_64/multiarch/wmemchr-evex-rtm.S

@@ -0,0 +1,3 @@
+#define MEMCHR __wmemchr_evex_rtm
+#define USE_AS_WMEMCHR 1
+#include "memchr-evex-rtm.S"

sysdeps/x86_64/multiarch/wmemchr.c

@@ -26,7 +26,7 @@
 # undef __wmemchr
 
 # define SYMBOL_NAME wmemchr
-# include "ifunc-avx2.h"
+# include "ifunc-evex.h"
 
 libc_ifunc_redirected (__redirect_wmemchr, __wmemchr, IFUNC_SELECTOR ());
 weak_alias (__wmemchr, wmemchr)