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glibc/sysdeps/x86_64/multiarch/memchr-evex.S
Noah Goldstein 104c7b1967 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>
2021-05-08 16:26:30 -04:00

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/* memchr/wmemchr optimized with 256-bit EVEX instructions.
Copyright (C) 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/>. */
#if IS_IN (libc)
# include <sysdep.h>
# ifndef MEMCHR
# define MEMCHR __memchr_evex
# endif
# ifdef USE_AS_WMEMCHR
# define VPBROADCAST vpbroadcastd
# define VPMINU vpminud
# define VPCMP vpcmpd
# define VPCMPEQ vpcmpeqd
# define CHAR_SIZE 4
# else
# define VPBROADCAST vpbroadcastb
# define VPMINU vpminub
# define VPCMP vpcmpb
# define VPCMPEQ vpcmpeqb
# 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
# define XMMZERO xmm23
# define YMMZERO ymm23
# define XMMMATCH xmm16
# define YMMMATCH ymm16
# define YMM1 ymm17
# define YMM2 ymm18
# define YMM3 ymm19
# define YMM4 ymm20
# 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 SECTION(.text),"ax",@progbits
ENTRY (MEMCHR)
# ifndef USE_AS_RAWMEMCHR
/* Check for zero length. */
test %RDX_LP, %RDX_LP
jz L(zero)
# ifdef __ILP32__
/* Clear the upper 32 bits. */
movl %edx, %edx
# endif
# endif
/* Broadcast CHAR to YMMMATCH. */
VPBROADCAST %esi, %YMMMATCH
/* Check if we may cross page boundary with one vector load. */
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. */
VPCMP $0, (%rdi), %YMMMATCH, %k0
kmovd %k0, %eax
# ifndef USE_AS_RAWMEMCHR
/* If length < CHAR_PER_VEC handle special. */
cmpq $CHAR_PER_VEC, %rdx
jbe L(first_vec_x0)
# endif
testl %eax, %eax
jz L(aligned_more)
tzcntl %eax, %eax
# ifdef USE_AS_WMEMCHR
/* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count. */
leaq (%rdi, %rax, CHAR_SIZE), %rax
# else
addq %rdi, %rax
# endif
ret
# ifndef USE_AS_RAWMEMCHR
L(zero):
xorl %eax, %eax
ret
.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, CHAR_SIZE), %rax
cmovle %rcx, %rax
ret
# else
/* NB: first_vec_x0 is 17 bytes which will leave
cross_page_boundary (which is relatively cold) close enough
to ideal alignment. So only realign L(cross_page_boundary) if
rawmemchr. */
.p2align 4
# endif
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. ALGN_PTR_REG is rcx for memchr and rdi
for rawmemchr. */
andq $-VEC_SIZE, %ALGN_PTR_REG
VPCMP $0, (%ALGN_PTR_REG), %YMMMATCH, %k0
kmovd %k0, %r8d
# ifdef USE_AS_WMEMCHR
/* NB: Divide shift count by 4 since each bit in K0 represent 4
bytes. */
sarl $2, %eax
# endif
# ifndef USE_AS_RAWMEMCHR
movl $(PAGE_SIZE / CHAR_SIZE), %esi
subl %eax, %esi
# endif
# ifdef USE_AS_WMEMCHR
andl $(CHAR_PER_VEC - 1), %eax
# endif
/* Remove the leading bytes. */
sarxl %eax, %r8d, %eax
# ifndef USE_AS_RAWMEMCHR
/* Check the end of data. */
cmpq %rsi, %rdx
jbe L(first_vec_x0)
# endif
testl %eax, %eax
jz L(cross_page_continue)
tzcntl %eax, %eax
# ifdef USE_AS_WMEMCHR
/* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count. */
leaq (%RAW_PTR_REG, %rax, CHAR_SIZE), %rax
# else
addq %RAW_PTR_REG, %rax
# endif
ret
.p2align 4
L(first_vec_x1):
tzcntl %eax, %eax
leaq VEC_SIZE(%rdi, %rax, CHAR_SIZE), %rax
ret
.p2align 4
L(first_vec_x2):
tzcntl %eax, %eax
leaq (VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %rax
ret
.p2align 4
L(first_vec_x3):
tzcntl %eax, %eax
leaq (VEC_SIZE * 3)(%rdi, %rax, CHAR_SIZE), %rax
ret
.p2align 4
L(first_vec_x4):
tzcntl %eax, %eax
leaq (VEC_SIZE * 4)(%rdi, %rax, CHAR_SIZE), %rax
ret
.p2align 5
L(aligned_more):
/* Check the first 4 * VEC_SIZE. Only one VEC_SIZE at a time
since data is only aligned to VEC_SIZE. */
# ifndef USE_AS_RAWMEMCHR
/* Align data to VEC_SIZE. */
L(cross_page_continue):
xorl %ecx, %ecx
subl %edi, %ecx
andq $-VEC_SIZE, %rdi
/* esi is for adjusting length to see if near the end. */
leal (VEC_SIZE * 5)(%rdi, %rcx), %esi
# ifdef USE_AS_WMEMCHR
/* NB: Divide bytes by 4 to get the wchar_t count. */
sarl $2, %esi
# endif
# else
andq $-VEC_SIZE, %rdi
L(cross_page_continue):
# endif
/* Load first VEC regardless. */
VPCMP $0, (VEC_SIZE)(%rdi), %YMMMATCH, %k0
kmovd %k0, %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)
VPCMP $0, (VEC_SIZE * 2)(%rdi), %YMMMATCH, %k0
kmovd %k0, %eax
testl %eax, %eax
jnz L(first_vec_x2)
VPCMP $0, (VEC_SIZE * 3)(%rdi), %YMMMATCH, %k0
kmovd %k0, %eax
testl %eax, %eax
jnz L(first_vec_x3)
VPCMP $0, (VEC_SIZE * 4)(%rdi), %YMMMATCH, %k0
kmovd %k0, %eax
testl %eax, %eax
jnz L(first_vec_x4)
# ifndef USE_AS_RAWMEMCHR
/* Check if at last CHAR_PER_VEC * 4 length. */
subq $(CHAR_PER_VEC * 4), %rdx
jbe L(last_4x_vec_or_less_cmpeq)
/* +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
subl %edi, %ecx
/* NB: Divide bytes by 4 to get the wchar_t count. */
sarl $2, %ecx
addq %rcx, %rdx
# else
addq %rdi, %rdx
andq $-(4 * VEC_SIZE), %rdi
subq %rdi, %rdx
# endif
# else
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
/* xor will set bytes match esi to zero. */
vpxorq (VEC_SIZE * 5)(%rdi), %YMMMATCH, %YMM2
vpxorq (VEC_SIZE * 6)(%rdi), %YMMMATCH, %YMM3
VPCMP $0, (VEC_SIZE * 7)(%rdi), %YMMMATCH, %k3
/* 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
jnz L(loop_4x_vec_end)
subq $-(VEC_SIZE * 4), %rdi
subq $(CHAR_PER_VEC * 4), %rdx
ja L(loop_4x_vec)
/* Fall through into less than 4 remaining vectors of length case.
*/
VPCMP $0, BASE_OFFSET(%rdi), %YMMMATCH, %k0
addq $(BASE_OFFSET - VEC_SIZE), %rdi
kmovd %k0, %eax
VZEROUPPER
L(last_4x_vec_or_less):
/* Check if first VEC contained match. */
testl %eax, %eax
jnz L(first_vec_x1_check)
/* If remaining length > CHAR_PER_VEC * 2. */
addl $(CHAR_PER_VEC * 2), %edx
jg L(last_4x_vec)
L(last_2x_vec):
/* If remaining length < CHAR_PER_VEC. */
addl $CHAR_PER_VEC, %edx
jle L(zero_end)
/* Check VEC2 and compare any match with remaining length. */
VPCMP $0, (VEC_SIZE * 2)(%rdi), %YMMMATCH, %k0
kmovd %k0, %eax
tzcntl %eax, %eax
cmpl %eax, %edx
jbe L(set_zero_end)
leaq (VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %rax
L(zero_end):
ret
.p2align 4
L(first_vec_x1_check):
tzcntl %eax, %eax
/* Adjust length. */
subl $-(CHAR_PER_VEC * 4), %edx
/* Check if match within remaining length. */
cmpl %eax, %edx
jbe L(set_zero_end)
/* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count. */
leaq VEC_SIZE(%rdi, %rax, CHAR_SIZE), %rax
ret
L(set_zero_end):
xorl %eax, %eax
ret
.p2align 4
L(loop_4x_vec_end):
# endif
/* 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
subl $((1 << CHAR_PER_VEC) - 1), %eax
# 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
leaq (VEC_SIZE * 3 + RET_OFFSET)(%rdi, %rax, CHAR_SIZE), %rax
# else
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
# if defined USE_AS_WMEMCHR || RET_OFFSET != 0
/* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count. */
leaq RET_OFFSET(%rdi, %rax, CHAR_SIZE), %rax
# else
addq %rdi, %rax
# endif
VZEROUPPER
ret
.p2align 4
L(last_vec_x2_return):
tzcntl %eax, %eax
/* NB: Multiply bytes by RET_SCALE to get the wchar_t count
if relevant (RET_SCALE = CHAR_SIZE if USE_AS_WMEMCHAR and
USE_IN_RTM are both defined. Otherwise RET_SCALE = 1. */
leaq (VEC_SIZE + RET_OFFSET)(%rdi, %rax, RET_SCALE), %rax
VZEROUPPER
ret
# ifdef USE_IN_RTM
.p2align 4
L(last_vec_x3_return):
tzcntl %eax, %eax
/* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count. */
leaq (VEC_SIZE * 2 + RET_OFFSET)(%rdi, %rax, CHAR_SIZE), %rax
ret
# endif
# ifndef USE_AS_RAWMEMCHR
L(last_4x_vec_or_less_cmpeq):
VPCMP $0, (VEC_SIZE * 5)(%rdi), %YMMMATCH, %k0
kmovd %k0, %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 $(CHAR_PER_VEC * 2), %edx
jle L(last_2x_vec)
.p2align 4
L(last_4x_vec):
VPCMP $0, (VEC_SIZE * 2)(%rdi), %YMMMATCH, %k0
kmovd %k0, %eax
testl %eax, %eax
jnz L(last_vec_x2)
VPCMP $0, (VEC_SIZE * 3)(%rdi), %YMMMATCH, %k0
kmovd %k0, %eax
/* Create mask for possible matches within remaining length. */
# ifdef USE_AS_WMEMCHR
movl $((1 << (CHAR_PER_VEC * 2)) - 1), %ecx
bzhil %edx, %ecx, %ecx
# else
movq $-1, %rcx
bzhiq %rdx, %rcx, %rcx
# endif
/* Test matches in data against length match. */
andl %ecx, %eax
jnz L(last_vec_x3)
/* if remaining length <= CHAR_PER_VEC * 3 (Note this is after
remaining length was found to be > CHAR_PER_VEC * 2. */
subl $CHAR_PER_VEC, %edx
jbe L(zero_end2)
VPCMP $0, (VEC_SIZE * 4)(%rdi), %YMMMATCH, %k0
kmovd %k0, %eax
/* Shift remaining length mask for last VEC. */
# ifdef USE_AS_WMEMCHR
shrl $CHAR_PER_VEC, %ecx
# else
shrq $CHAR_PER_VEC, %rcx
# endif
andl %ecx, %eax
jz L(zero_end2)
tzcntl %eax, %eax
leaq (VEC_SIZE * 4)(%rdi, %rax, CHAR_SIZE), %rax
L(zero_end2):
ret
L(last_vec_x2):
tzcntl %eax, %eax
leaq (VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %rax
ret
.p2align 4
L(last_vec_x3):
tzcntl %eax, %eax
leaq (VEC_SIZE * 3)(%rdi, %rax, CHAR_SIZE), %rax
ret
# endif
END (MEMCHR)
#endif
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