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glibc/sysdeps/x86_64/multiarch/strcmp-avx2.S
Noah Goldstein b77b06e0e2 x86: Optimize strcmp-avx2.S 
Optimization are primarily to the loop logic and how the page cross
logic interacts with the loop.

The page cross logic is at times more expensive for short strings near
the end of a page but not crossing the page. This is done to retest
the page cross conditions with a non-faulty check and to improve the
logic for entering the loop afterwards. This is only particular cases,
however, and is general made up for by more than 10x improvements on
the transition from the page cross -> loop case.

The non-page cross cases are improved most for smaller sizes [0, 128]
and go about even for (128, 4096]. The loop page cross logic is
improved so some more significant speedup is seen there as well.

test-strcmp, test-strncmp, test-wcscmp, and test-wcsncmp all pass.

Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
2022-02-03 16:41:38 -06:00

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/* strcmp/wcscmp/strncmp/wcsncmp optimized with AVX2.
Copyright (C) 2018-2022 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/>. */
#if IS_IN (libc)
# include <sysdep.h>
# ifndef STRCMP
# define STRCMP __strcmp_avx2
# endif
# define PAGE_SIZE 4096
/* VEC_SIZE = Number of bytes in a ymm register. */
# define VEC_SIZE 32
# define VMOVU vmovdqu
# define VMOVA vmovdqa
# ifdef USE_AS_WCSCMP
/* Compare packed dwords. */
# define VPCMPEQ vpcmpeqd
/* Compare packed dwords and store minimum. */
# define VPMINU vpminud
/* 1 dword char == 4 bytes. */
# define SIZE_OF_CHAR 4
# else
/* Compare packed bytes. */
# define VPCMPEQ vpcmpeqb
/* Compare packed bytes and store minimum. */
# define VPMINU vpminub
/* 1 byte char == 1 byte. */
# define SIZE_OF_CHAR 1
# endif
# ifdef USE_AS_STRNCMP
# define LOOP_REG r9d
# define LOOP_REG64 r9
# define OFFSET_REG8 r9b
# define OFFSET_REG r9d
# define OFFSET_REG64 r9
# else
# define LOOP_REG edx
# define LOOP_REG64 rdx
# define OFFSET_REG8 dl
# define OFFSET_REG edx
# define OFFSET_REG64 rdx
# endif
# ifndef VZEROUPPER
# define VZEROUPPER vzeroupper
# endif
# if defined USE_AS_STRNCMP
# define VEC_OFFSET 0
# else
# define VEC_OFFSET (-VEC_SIZE)
# endif
# define xmmZERO xmm15
# define ymmZERO ymm15
# ifndef SECTION
# define SECTION(p) p##.avx
# endif
/* Warning!
wcscmp/wcsncmp have to use SIGNED comparison for elements.
strcmp/strncmp have to use UNSIGNED comparison for elements.
*/
/* The main idea of the string comparison (byte or dword) using AVX2
consists of comparing (VPCMPEQ) two ymm vectors. The latter can be on
either packed bytes or dwords depending on USE_AS_WCSCMP. In order
to check the null char, algorithm keeps the matched bytes/dwords,
requiring two more AVX2 instructions (VPMINU and VPCMPEQ). In general,
the costs of comparing VEC_SIZE bytes (32-bytes) are two VPCMPEQ and
one VPMINU instructions, together with movdqu and testl instructions.
Main loop (away from from page boundary) compares 4 vectors are a time,
effectively comparing 4 x VEC_SIZE bytes (128 bytes) on each loop.
The routine strncmp/wcsncmp (enabled by defining USE_AS_STRNCMP) logic
is the same as strcmp, except that an a maximum offset is tracked. If
the maximum offset is reached before a difference is found, zero is
returned. */
.section SECTION(.text), "ax", @progbits
ENTRY(STRCMP)
# ifdef USE_AS_STRNCMP
# ifdef __ILP32__
/* Clear the upper 32 bits. */
movl %edx, %rdx
# endif
cmp $1, %RDX_LP
/* Signed comparison intentional. We use this branch to also
test cases where length >= 2^63. These very large sizes can be
handled with strcmp as there is no way for that length to
actually bound the buffer. */
jle L(one_or_less)
# ifdef USE_AS_WCSCMP
movq %rdx, %rcx
/* Multiplying length by sizeof(wchar_t) can result in overflow.
Check if that is possible. All cases where overflow are possible
are cases where length is large enough that it can never be a
bound on valid memory so just use wcscmp. */
shrq $56, %rcx
jnz __wcscmp_avx2
leaq (, %rdx, 4), %rdx
# endif
# endif
vpxor %xmmZERO, %xmmZERO, %xmmZERO
movl %edi, %eax
orl %esi, %eax
sall $20, %eax
/* Check if s1 or s2 may cross a page in next 4x VEC loads. */
cmpl $((PAGE_SIZE -(VEC_SIZE * 4)) << 20), %eax
ja L(page_cross)
L(no_page_cross):
/* Safe to compare 4x vectors. */
VMOVU (%rdi), %ymm0
/* 1s where s1 and s2 equal. */
VPCMPEQ (%rsi), %ymm0, %ymm1
/* 1s at null CHAR. */
VPCMPEQ %ymm0, %ymmZERO, %ymm2
/* 1s where s1 and s2 equal AND not null CHAR. */
vpandn %ymm1, %ymm2, %ymm1
/* All 1s -> keep going, any 0s -> return. */
vpmovmskb %ymm1, %ecx
# ifdef USE_AS_STRNCMP
cmpq $VEC_SIZE, %rdx
jbe L(vec_0_test_len)
# endif
/* All 1s represents all equals. incl will overflow to zero in
all equals case. Otherwise 1s will carry until position of first
mismatch. */
incl %ecx
jz L(more_3x_vec)
.p2align 4,, 4
L(return_vec_0):
tzcntl %ecx, %ecx
# ifdef USE_AS_WCSCMP
movl (%rdi, %rcx), %edx
xorl %eax, %eax
cmpl (%rsi, %rcx), %edx
je L(ret0)
setl %al
negl %eax
orl $1, %eax
# else
movzbl (%rdi, %rcx), %eax
movzbl (%rsi, %rcx), %ecx
subl %ecx, %eax
# endif
L(ret0):
L(return_vzeroupper):
ZERO_UPPER_VEC_REGISTERS_RETURN
# ifdef USE_AS_STRNCMP
.p2align 4,, 8
L(vec_0_test_len):
notl %ecx
bzhil %edx, %ecx, %eax
jnz L(return_vec_0)
/* Align if will cross fetch block. */
.p2align 4,, 2
L(ret_zero):
xorl %eax, %eax
VZEROUPPER_RETURN
.p2align 4,, 5
L(one_or_less):
jb L(ret_zero)
# ifdef USE_AS_WCSCMP
/* 'nbe' covers the case where length is negative (large
unsigned). */
jnbe __wcscmp_avx2
movl (%rdi), %edx
xorl %eax, %eax
cmpl (%rsi), %edx
je L(ret1)
setl %al
negl %eax
orl $1, %eax
# else
/* 'nbe' covers the case where length is negative (large
unsigned). */
jnbe __strcmp_avx2
movzbl (%rdi), %eax
movzbl (%rsi), %ecx
subl %ecx, %eax
# endif
L(ret1):
ret
# endif
.p2align 4,, 10
L(return_vec_1):
tzcntl %ecx, %ecx
# ifdef USE_AS_STRNCMP
/* rdx must be > CHAR_PER_VEC so save to subtract w.o fear of
overflow. */
addq $-VEC_SIZE, %rdx
cmpq %rcx, %rdx
jbe L(ret_zero)
# endif
# ifdef USE_AS_WCSCMP
movl VEC_SIZE(%rdi, %rcx), %edx
xorl %eax, %eax
cmpl VEC_SIZE(%rsi, %rcx), %edx
je L(ret2)
setl %al
negl %eax
orl $1, %eax
# else
movzbl VEC_SIZE(%rdi, %rcx), %eax
movzbl VEC_SIZE(%rsi, %rcx), %ecx
subl %ecx, %eax
# endif
L(ret2):
VZEROUPPER_RETURN
.p2align 4,, 10
# ifdef USE_AS_STRNCMP
L(return_vec_3):
salq $32, %rcx
# endif
L(return_vec_2):
# ifndef USE_AS_STRNCMP
tzcntl %ecx, %ecx
# else
tzcntq %rcx, %rcx
cmpq %rcx, %rdx
jbe L(ret_zero)
# endif
# ifdef USE_AS_WCSCMP
movl (VEC_SIZE * 2)(%rdi, %rcx), %edx
xorl %eax, %eax
cmpl (VEC_SIZE * 2)(%rsi, %rcx), %edx
je L(ret3)
setl %al
negl %eax
orl $1, %eax
# else
movzbl (VEC_SIZE * 2)(%rdi, %rcx), %eax
movzbl (VEC_SIZE * 2)(%rsi, %rcx), %ecx
subl %ecx, %eax
# endif
L(ret3):
VZEROUPPER_RETURN
# ifndef USE_AS_STRNCMP
.p2align 4,, 10
L(return_vec_3):
tzcntl %ecx, %ecx
# ifdef USE_AS_WCSCMP
movl (VEC_SIZE * 3)(%rdi, %rcx), %edx
xorl %eax, %eax
cmpl (VEC_SIZE * 3)(%rsi, %rcx), %edx
je L(ret4)
setl %al
negl %eax
orl $1, %eax
# else
movzbl (VEC_SIZE * 3)(%rdi, %rcx), %eax
movzbl (VEC_SIZE * 3)(%rsi, %rcx), %ecx
subl %ecx, %eax
# endif
L(ret4):
VZEROUPPER_RETURN
# endif
.p2align 4,, 10
L(more_3x_vec):
/* Safe to compare 4x vectors. */
VMOVU VEC_SIZE(%rdi), %ymm0
VPCMPEQ VEC_SIZE(%rsi), %ymm0, %ymm1
VPCMPEQ %ymm0, %ymmZERO, %ymm2
vpandn %ymm1, %ymm2, %ymm1
vpmovmskb %ymm1, %ecx
incl %ecx
jnz L(return_vec_1)
# ifdef USE_AS_STRNCMP
subq $(VEC_SIZE * 2), %rdx
jbe L(ret_zero)
# endif
VMOVU (VEC_SIZE * 2)(%rdi), %ymm0
VPCMPEQ (VEC_SIZE * 2)(%rsi), %ymm0, %ymm1
VPCMPEQ %ymm0, %ymmZERO, %ymm2
vpandn %ymm1, %ymm2, %ymm1
vpmovmskb %ymm1, %ecx
incl %ecx
jnz L(return_vec_2)
VMOVU (VEC_SIZE * 3)(%rdi), %ymm0
VPCMPEQ (VEC_SIZE * 3)(%rsi), %ymm0, %ymm1
VPCMPEQ %ymm0, %ymmZERO, %ymm2
vpandn %ymm1, %ymm2, %ymm1
vpmovmskb %ymm1, %ecx
incl %ecx
jnz L(return_vec_3)
# ifdef USE_AS_STRNCMP
cmpq $(VEC_SIZE * 2), %rdx
jbe L(ret_zero)
# endif
# ifdef USE_AS_WCSCMP
/* any non-zero positive value that doesn't inference with 0x1.
*/
movl $2, %r8d
# else
xorl %r8d, %r8d
# endif
/* The prepare labels are various entry points from the page
cross logic. */
L(prepare_loop):
# ifdef USE_AS_STRNCMP
/* Store N + (VEC_SIZE * 4) and place check at the begining of
the loop. */
leaq (VEC_SIZE * 2)(%rdi, %rdx), %rdx
# endif
L(prepare_loop_no_len):
/* Align s1 and adjust s2 accordingly. */
subq %rdi, %rsi
andq $-(VEC_SIZE * 4), %rdi
addq %rdi, %rsi
# ifdef USE_AS_STRNCMP
subq %rdi, %rdx
# endif
L(prepare_loop_aligned):
/* eax stores distance from rsi to next page cross. These cases
need to be handled specially as the 4x loop could potentially
read memory past the length of s1 or s2 and across a page
boundary. */
movl $-(VEC_SIZE * 4), %eax
subl %esi, %eax
andl $(PAGE_SIZE - 1), %eax
/* Loop 4x comparisons at a time. */
.p2align 4
L(loop):
/* End condition for strncmp. */
# ifdef USE_AS_STRNCMP
subq $(VEC_SIZE * 4), %rdx
jbe L(ret_zero)
# endif
subq $-(VEC_SIZE * 4), %rdi
subq $-(VEC_SIZE * 4), %rsi
/* Check if rsi loads will cross a page boundary. */
addl $-(VEC_SIZE * 4), %eax
jnb L(page_cross_during_loop)
/* Loop entry after handling page cross during loop. */
L(loop_skip_page_cross_check):
VMOVA (VEC_SIZE * 0)(%rdi), %ymm0
VMOVA (VEC_SIZE * 1)(%rdi), %ymm2
VMOVA (VEC_SIZE * 2)(%rdi), %ymm4
VMOVA (VEC_SIZE * 3)(%rdi), %ymm6
/* ymm1 all 1s where s1 and s2 equal. All 0s otherwise. */
VPCMPEQ (VEC_SIZE * 0)(%rsi), %ymm0, %ymm1
VPCMPEQ (VEC_SIZE * 1)(%rsi), %ymm2, %ymm3
VPCMPEQ (VEC_SIZE * 2)(%rsi), %ymm4, %ymm5
VPCMPEQ (VEC_SIZE * 3)(%rsi), %ymm6, %ymm7
/* If any mismatches or null CHAR then 0 CHAR, otherwise non-
zero. */
vpand %ymm0, %ymm1, %ymm1
vpand %ymm2, %ymm3, %ymm3
vpand %ymm4, %ymm5, %ymm5
vpand %ymm6, %ymm7, %ymm7
VPMINU %ymm1, %ymm3, %ymm3
VPMINU %ymm5, %ymm7, %ymm7
/* Reduce all 0 CHARs for the 4x VEC into ymm7. */
VPMINU %ymm3, %ymm7, %ymm7
/* If any 0 CHAR then done. */
VPCMPEQ %ymm7, %ymmZERO, %ymm7
vpmovmskb %ymm7, %LOOP_REG
testl %LOOP_REG, %LOOP_REG
jz L(loop)
/* Find which VEC has the mismatch of end of string. */
VPCMPEQ %ymm1, %ymmZERO, %ymm1
vpmovmskb %ymm1, %ecx
testl %ecx, %ecx
jnz L(return_vec_0_end)
VPCMPEQ %ymm3, %ymmZERO, %ymm3
vpmovmskb %ymm3, %ecx
testl %ecx, %ecx
jnz L(return_vec_1_end)
L(return_vec_2_3_end):
# ifdef USE_AS_STRNCMP
subq $(VEC_SIZE * 2), %rdx
jbe L(ret_zero_end)
# endif
VPCMPEQ %ymm5, %ymmZERO, %ymm5
vpmovmskb %ymm5, %ecx
testl %ecx, %ecx
jnz L(return_vec_2_end)
/* LOOP_REG contains matches for null/mismatch from the loop. If
VEC 0,1,and 2 all have no null and no mismatches then mismatch
must entirely be from VEC 3 which is fully represented by
LOOP_REG. */
tzcntl %LOOP_REG, %LOOP_REG
# ifdef USE_AS_STRNCMP
subl $-(VEC_SIZE), %LOOP_REG
cmpq %LOOP_REG64, %rdx
jbe L(ret_zero_end)
# endif
# ifdef USE_AS_WCSCMP
movl (VEC_SIZE * 2 - VEC_OFFSET)(%rdi, %LOOP_REG64), %ecx
xorl %eax, %eax
cmpl (VEC_SIZE * 2 - VEC_OFFSET)(%rsi, %LOOP_REG64), %ecx
je L(ret5)
setl %al
negl %eax
xorl %r8d, %eax
# else
movzbl (VEC_SIZE * 2 - VEC_OFFSET)(%rdi, %LOOP_REG64), %eax
movzbl (VEC_SIZE * 2 - VEC_OFFSET)(%rsi, %LOOP_REG64), %ecx
subl %ecx, %eax
xorl %r8d, %eax
subl %r8d, %eax
# endif
L(ret5):
VZEROUPPER_RETURN
# ifdef USE_AS_STRNCMP
.p2align 4,, 2
L(ret_zero_end):
xorl %eax, %eax
VZEROUPPER_RETURN
# endif
/* The L(return_vec_N_end) differ from L(return_vec_N) in that
they use the value of `r8` to negate the return value. This is
because the page cross logic can swap `rdi` and `rsi`. */
.p2align 4,, 10
# ifdef USE_AS_STRNCMP
L(return_vec_1_end):
salq $32, %rcx
# endif
L(return_vec_0_end):
# ifndef USE_AS_STRNCMP
tzcntl %ecx, %ecx
# else
tzcntq %rcx, %rcx
cmpq %rcx, %rdx
jbe L(ret_zero_end)
# endif
# ifdef USE_AS_WCSCMP
movl (%rdi, %rcx), %edx
xorl %eax, %eax
cmpl (%rsi, %rcx), %edx
je L(ret6)
setl %al
negl %eax
xorl %r8d, %eax
# else
movzbl (%rdi, %rcx), %eax
movzbl (%rsi, %rcx), %ecx
subl %ecx, %eax
xorl %r8d, %eax
subl %r8d, %eax
# endif
L(ret6):
VZEROUPPER_RETURN
# ifndef USE_AS_STRNCMP
.p2align 4,, 10
L(return_vec_1_end):
tzcntl %ecx, %ecx
# ifdef USE_AS_WCSCMP
movl VEC_SIZE(%rdi, %rcx), %edx
xorl %eax, %eax
cmpl VEC_SIZE(%rsi, %rcx), %edx
je L(ret7)
setl %al
negl %eax
xorl %r8d, %eax
# else
movzbl VEC_SIZE(%rdi, %rcx), %eax
movzbl VEC_SIZE(%rsi, %rcx), %ecx
subl %ecx, %eax
xorl %r8d, %eax
subl %r8d, %eax
# endif
L(ret7):
VZEROUPPER_RETURN
# endif
.p2align 4,, 10
L(return_vec_2_end):
tzcntl %ecx, %ecx
# ifdef USE_AS_STRNCMP
cmpq %rcx, %rdx
jbe L(ret_zero_page_cross)
# endif
# ifdef USE_AS_WCSCMP
movl (VEC_SIZE * 2)(%rdi, %rcx), %edx
xorl %eax, %eax
cmpl (VEC_SIZE * 2)(%rsi, %rcx), %edx
je L(ret11)
setl %al
negl %eax
xorl %r8d, %eax
# else
movzbl (VEC_SIZE * 2)(%rdi, %rcx), %eax
movzbl (VEC_SIZE * 2)(%rsi, %rcx), %ecx
subl %ecx, %eax
xorl %r8d, %eax
subl %r8d, %eax
# endif
L(ret11):
VZEROUPPER_RETURN
/* Page cross in rsi in next 4x VEC. */
/* TODO: Improve logic here. */
.p2align 4,, 10
L(page_cross_during_loop):
/* eax contains [distance_from_page - (VEC_SIZE * 4)]. */
/* Optimistically rsi and rdi and both aligned inwhich case we
don't need any logic here. */
cmpl $-(VEC_SIZE * 4), %eax
/* Don't adjust eax before jumping back to loop and we will
never hit page cross case again. */
je L(loop_skip_page_cross_check)
/* Check if we can safely load a VEC. */
cmpl $-(VEC_SIZE * 3), %eax
jle L(less_1x_vec_till_page_cross)
VMOVA (%rdi), %ymm0
VPCMPEQ (%rsi), %ymm0, %ymm1
VPCMPEQ %ymm0, %ymmZERO, %ymm2
vpandn %ymm1, %ymm2, %ymm1
vpmovmskb %ymm1, %ecx
incl %ecx
jnz L(return_vec_0_end)
/* if distance >= 2x VEC then eax > -(VEC_SIZE * 2). */
cmpl $-(VEC_SIZE * 2), %eax
jg L(more_2x_vec_till_page_cross)
.p2align 4,, 4
L(less_1x_vec_till_page_cross):
subl $-(VEC_SIZE * 4), %eax
/* Guranteed safe to read from rdi - VEC_SIZE here. The only
concerning case is first iteration if incoming s1 was near start
of a page and s2 near end. If s1 was near the start of the page
we already aligned up to nearest VEC_SIZE * 4 so gurnateed safe
to read back -VEC_SIZE. If rdi is truly at the start of a page
here, it means the previous page (rdi - VEC_SIZE) has already
been loaded earlier so must be valid. */
VMOVU -VEC_SIZE(%rdi, %rax), %ymm0
VPCMPEQ -VEC_SIZE(%rsi, %rax), %ymm0, %ymm1
VPCMPEQ %ymm0, %ymmZERO, %ymm2
vpandn %ymm1, %ymm2, %ymm1
vpmovmskb %ymm1, %ecx
/* Mask of potentially valid bits. The lower bits can be out of
range comparisons (but safe regarding page crosses). */
movl $-1, %r10d
shlxl %esi, %r10d, %r10d
notl %ecx
# ifdef USE_AS_STRNCMP
cmpq %rax, %rdx
jbe L(return_page_cross_end_check)
# endif
movl %eax, %OFFSET_REG
addl $(PAGE_SIZE - VEC_SIZE * 4), %eax
andl %r10d, %ecx
jz L(loop_skip_page_cross_check)
.p2align 4,, 3
L(return_page_cross_end):
tzcntl %ecx, %ecx
# ifdef USE_AS_STRNCMP
leal -VEC_SIZE(%OFFSET_REG64, %rcx), %ecx
L(return_page_cross_cmp_mem):
# else
addl %OFFSET_REG, %ecx
# endif
# ifdef USE_AS_WCSCMP
movl VEC_OFFSET(%rdi, %rcx), %edx
xorl %eax, %eax
cmpl VEC_OFFSET(%rsi, %rcx), %edx
je L(ret8)
setl %al
negl %eax
xorl %r8d, %eax
# else
movzbl VEC_OFFSET(%rdi, %rcx), %eax
movzbl VEC_OFFSET(%rsi, %rcx), %ecx
subl %ecx, %eax
xorl %r8d, %eax
subl %r8d, %eax
# endif
L(ret8):
VZEROUPPER_RETURN
# ifdef USE_AS_STRNCMP
.p2align 4,, 10
L(return_page_cross_end_check):
tzcntl %ecx, %ecx
leal -VEC_SIZE(%rax, %rcx), %ecx
cmpl %ecx, %edx
ja L(return_page_cross_cmp_mem)
xorl %eax, %eax
VZEROUPPER_RETURN
# endif
.p2align 4,, 10
L(more_2x_vec_till_page_cross):
/* If more 2x vec till cross we will complete a full loop
iteration here. */
VMOVU VEC_SIZE(%rdi), %ymm0
VPCMPEQ VEC_SIZE(%rsi), %ymm0, %ymm1
VPCMPEQ %ymm0, %ymmZERO, %ymm2
vpandn %ymm1, %ymm2, %ymm1
vpmovmskb %ymm1, %ecx
incl %ecx
jnz L(return_vec_1_end)
# ifdef USE_AS_STRNCMP
cmpq $(VEC_SIZE * 2), %rdx
jbe L(ret_zero_in_loop_page_cross)
# endif
subl $-(VEC_SIZE * 4), %eax
/* Safe to include comparisons from lower bytes. */
VMOVU -(VEC_SIZE * 2)(%rdi, %rax), %ymm0
VPCMPEQ -(VEC_SIZE * 2)(%rsi, %rax), %ymm0, %ymm1
VPCMPEQ %ymm0, %ymmZERO, %ymm2
vpandn %ymm1, %ymm2, %ymm1
vpmovmskb %ymm1, %ecx
incl %ecx
jnz L(return_vec_page_cross_0)
VMOVU -(VEC_SIZE * 1)(%rdi, %rax), %ymm0
VPCMPEQ -(VEC_SIZE * 1)(%rsi, %rax), %ymm0, %ymm1
VPCMPEQ %ymm0, %ymmZERO, %ymm2
vpandn %ymm1, %ymm2, %ymm1
vpmovmskb %ymm1, %ecx
incl %ecx
jnz L(return_vec_page_cross_1)
# ifdef USE_AS_STRNCMP
/* Must check length here as length might proclude reading next
page. */
cmpq %rax, %rdx
jbe L(ret_zero_in_loop_page_cross)
# endif
/* Finish the loop. */
VMOVA (VEC_SIZE * 2)(%rdi), %ymm4
VMOVA (VEC_SIZE * 3)(%rdi), %ymm6
VPCMPEQ (VEC_SIZE * 2)(%rsi), %ymm4, %ymm5
VPCMPEQ (VEC_SIZE * 3)(%rsi), %ymm6, %ymm7
vpand %ymm4, %ymm5, %ymm5
vpand %ymm6, %ymm7, %ymm7
VPMINU %ymm5, %ymm7, %ymm7
VPCMPEQ %ymm7, %ymmZERO, %ymm7
vpmovmskb %ymm7, %LOOP_REG
testl %LOOP_REG, %LOOP_REG
jnz L(return_vec_2_3_end)
/* Best for code size to include ucond-jmp here. Would be faster
if this case is hot to duplicate the L(return_vec_2_3_end) code
as fall-through and have jump back to loop on mismatch
comparison. */
subq $-(VEC_SIZE * 4), %rdi
subq $-(VEC_SIZE * 4), %rsi
addl $(PAGE_SIZE - VEC_SIZE * 8), %eax
# ifdef USE_AS_STRNCMP
subq $(VEC_SIZE * 4), %rdx
ja L(loop_skip_page_cross_check)
L(ret_zero_in_loop_page_cross):
xorl %eax, %eax
VZEROUPPER_RETURN
# else
jmp L(loop_skip_page_cross_check)
# endif
.p2align 4,, 10
L(return_vec_page_cross_0):
addl $-VEC_SIZE, %eax
L(return_vec_page_cross_1):
tzcntl %ecx, %ecx
# ifdef USE_AS_STRNCMP
leal -VEC_SIZE(%rax, %rcx), %ecx
cmpq %rcx, %rdx
jbe L(ret_zero_in_loop_page_cross)
# else
addl %eax, %ecx
# endif
# ifdef USE_AS_WCSCMP
movl VEC_OFFSET(%rdi, %rcx), %edx
xorl %eax, %eax
cmpl VEC_OFFSET(%rsi, %rcx), %edx
je L(ret9)
setl %al
negl %eax
xorl %r8d, %eax
# else
movzbl VEC_OFFSET(%rdi, %rcx), %eax
movzbl VEC_OFFSET(%rsi, %rcx), %ecx
subl %ecx, %eax
xorl %r8d, %eax
subl %r8d, %eax
# endif
L(ret9):
VZEROUPPER_RETURN
.p2align 4,, 10
L(page_cross):
# ifndef USE_AS_STRNCMP
/* If both are VEC aligned we don't need any special logic here.
Only valid for strcmp where stop condition is guranteed to be
reachable by just reading memory. */
testl $((VEC_SIZE - 1) << 20), %eax
jz L(no_page_cross)
# endif
movl %edi, %eax
movl %esi, %ecx
andl $(PAGE_SIZE - 1), %eax
andl $(PAGE_SIZE - 1), %ecx
xorl %OFFSET_REG, %OFFSET_REG
/* Check which is closer to page cross, s1 or s2. */
cmpl %eax, %ecx
jg L(page_cross_s2)
/* The previous page cross check has false positives. Check for
true positive as page cross logic is very expensive. */
subl $(PAGE_SIZE - VEC_SIZE * 4), %eax
jbe L(no_page_cross)
/* Set r8 to not interfere with normal return value (rdi and rsi
did not swap). */
# ifdef USE_AS_WCSCMP
/* any non-zero positive value that doesn't inference with 0x1.
*/
movl $2, %r8d
# else
xorl %r8d, %r8d
# endif
/* Check if less than 1x VEC till page cross. */
subl $(VEC_SIZE * 3), %eax
jg L(less_1x_vec_till_page)
/* If more than 1x VEC till page cross, loop throuh safely
loadable memory until within 1x VEC of page cross. */
.p2align 4,, 10
L(page_cross_loop):
VMOVU (%rdi, %OFFSET_REG64), %ymm0
VPCMPEQ (%rsi, %OFFSET_REG64), %ymm0, %ymm1
VPCMPEQ %ymm0, %ymmZERO, %ymm2
vpandn %ymm1, %ymm2, %ymm1
vpmovmskb %ymm1, %ecx
incl %ecx
jnz L(check_ret_vec_page_cross)
addl $VEC_SIZE, %OFFSET_REG
# ifdef USE_AS_STRNCMP
cmpq %OFFSET_REG64, %rdx
jbe L(ret_zero_page_cross)
# endif
addl $VEC_SIZE, %eax
jl L(page_cross_loop)
subl %eax, %OFFSET_REG
/* OFFSET_REG has distance to page cross - VEC_SIZE. Guranteed
to not cross page so is safe to load. Since we have already
loaded at least 1 VEC from rsi it is also guranteed to be safe.
*/
VMOVU (%rdi, %OFFSET_REG64), %ymm0
VPCMPEQ (%rsi, %OFFSET_REG64), %ymm0, %ymm1
VPCMPEQ %ymm0, %ymmZERO, %ymm2
vpandn %ymm1, %ymm2, %ymm1
vpmovmskb %ymm1, %ecx
# ifdef USE_AS_STRNCMP
leal VEC_SIZE(%OFFSET_REG64), %eax
cmpq %rax, %rdx
jbe L(check_ret_vec_page_cross2)
addq %rdi, %rdx
# endif
incl %ecx
jz L(prepare_loop_no_len)
.p2align 4,, 4
L(ret_vec_page_cross):
# ifndef USE_AS_STRNCMP
L(check_ret_vec_page_cross):
# endif
tzcntl %ecx, %ecx
addl %OFFSET_REG, %ecx
L(ret_vec_page_cross_cont):
# ifdef USE_AS_WCSCMP
movl (%rdi, %rcx), %edx
xorl %eax, %eax
cmpl (%rsi, %rcx), %edx
je L(ret12)
setl %al
negl %eax
xorl %r8d, %eax
# else
movzbl (%rdi, %rcx), %eax
movzbl (%rsi, %rcx), %ecx
subl %ecx, %eax
xorl %r8d, %eax
subl %r8d, %eax
# endif
L(ret12):
VZEROUPPER_RETURN
# ifdef USE_AS_STRNCMP
.p2align 4,, 10
L(check_ret_vec_page_cross2):
incl %ecx
L(check_ret_vec_page_cross):
tzcntl %ecx, %ecx
addl %OFFSET_REG, %ecx
cmpq %rcx, %rdx
ja L(ret_vec_page_cross_cont)
.p2align 4,, 2
L(ret_zero_page_cross):
xorl %eax, %eax
VZEROUPPER_RETURN
# endif
.p2align 4,, 4
L(page_cross_s2):
/* Ensure this is a true page cross. */
subl $(PAGE_SIZE - VEC_SIZE * 4), %ecx
jbe L(no_page_cross)
movl %ecx, %eax
movq %rdi, %rcx
movq %rsi, %rdi
movq %rcx, %rsi
/* set r8 to negate return value as rdi and rsi swapped. */
# ifdef USE_AS_WCSCMP
movl $-4, %r8d
# else
movl $-1, %r8d
# endif
xorl %OFFSET_REG, %OFFSET_REG
/* Check if more than 1x VEC till page cross. */
subl $(VEC_SIZE * 3), %eax
jle L(page_cross_loop)
.p2align 4,, 6
L(less_1x_vec_till_page):
/* Find largest load size we can use. */
cmpl $16, %eax
ja L(less_16_till_page)
VMOVU (%rdi), %xmm0
VPCMPEQ (%rsi), %xmm0, %xmm1
VPCMPEQ %xmm0, %xmmZERO, %xmm2
vpandn %xmm1, %xmm2, %xmm1
vpmovmskb %ymm1, %ecx
incw %cx
jnz L(check_ret_vec_page_cross)
movl $16, %OFFSET_REG
# ifdef USE_AS_STRNCMP
cmpq %OFFSET_REG64, %rdx
jbe L(ret_zero_page_cross_slow_case0)
subl %eax, %OFFSET_REG
# else
/* Explicit check for 16 byte alignment. */
subl %eax, %OFFSET_REG
jz L(prepare_loop)
# endif
VMOVU (%rdi, %OFFSET_REG64), %xmm0
VPCMPEQ (%rsi, %OFFSET_REG64), %xmm0, %xmm1
VPCMPEQ %xmm0, %xmmZERO, %xmm2
vpandn %xmm1, %xmm2, %xmm1
vpmovmskb %ymm1, %ecx
incw %cx
jnz L(check_ret_vec_page_cross)
# ifdef USE_AS_STRNCMP
addl $16, %OFFSET_REG
subq %OFFSET_REG64, %rdx
jbe L(ret_zero_page_cross_slow_case0)
subq $-(VEC_SIZE * 4), %rdx
leaq -(VEC_SIZE * 4)(%rdi, %OFFSET_REG64), %rdi
leaq -(VEC_SIZE * 4)(%rsi, %OFFSET_REG64), %rsi
# else
leaq (16 - VEC_SIZE * 4)(%rdi, %OFFSET_REG64), %rdi
leaq (16 - VEC_SIZE * 4)(%rsi, %OFFSET_REG64), %rsi
# endif
jmp L(prepare_loop_aligned)
# ifdef USE_AS_STRNCMP
.p2align 4,, 2
L(ret_zero_page_cross_slow_case0):
xorl %eax, %eax
ret
# endif
.p2align 4,, 10
L(less_16_till_page):
/* Find largest load size we can use. */
cmpl $24, %eax
ja L(less_8_till_page)
vmovq (%rdi), %xmm0
vmovq (%rsi), %xmm1
VPCMPEQ %xmm0, %xmmZERO, %xmm2
VPCMPEQ %xmm1, %xmm0, %xmm1
vpandn %xmm1, %xmm2, %xmm1
vpmovmskb %ymm1, %ecx
incb %cl
jnz L(check_ret_vec_page_cross)
# ifdef USE_AS_STRNCMP
cmpq $8, %rdx
jbe L(ret_zero_page_cross_slow_case0)
# endif
movl $24, %OFFSET_REG
/* Explicit check for 16 byte alignment. */
subl %eax, %OFFSET_REG
vmovq (%rdi, %OFFSET_REG64), %xmm0
vmovq (%rsi, %OFFSET_REG64), %xmm1
VPCMPEQ %xmm0, %xmmZERO, %xmm2
VPCMPEQ %xmm1, %xmm0, %xmm1
vpandn %xmm1, %xmm2, %xmm1
vpmovmskb %ymm1, %ecx
incb %cl
jnz L(check_ret_vec_page_cross)
# ifdef USE_AS_STRNCMP
addl $8, %OFFSET_REG
subq %OFFSET_REG64, %rdx
jbe L(ret_zero_page_cross_slow_case0)
subq $-(VEC_SIZE * 4), %rdx
leaq -(VEC_SIZE * 4)(%rdi, %OFFSET_REG64), %rdi
leaq -(VEC_SIZE * 4)(%rsi, %OFFSET_REG64), %rsi
# else
leaq (8 - VEC_SIZE * 4)(%rdi, %OFFSET_REG64), %rdi
leaq (8 - VEC_SIZE * 4)(%rsi, %OFFSET_REG64), %rsi
# endif
jmp L(prepare_loop_aligned)
.p2align 4,, 10
L(less_8_till_page):
# ifdef USE_AS_WCSCMP
/* If using wchar then this is the only check before we reach
the page boundary. */
movl (%rdi), %eax
movl (%rsi), %ecx
cmpl %ecx, %eax
jnz L(ret_less_8_wcs)
# ifdef USE_AS_STRNCMP
addq %rdi, %rdx
/* We already checked for len <= 1 so cannot hit that case here.
*/
# endif
testl %eax, %eax
jnz L(prepare_loop_no_len)
ret
.p2align 4,, 8
L(ret_less_8_wcs):
setl %OFFSET_REG8
negl %OFFSET_REG
movl %OFFSET_REG, %eax
xorl %r8d, %eax
ret
# else
/* Find largest load size we can use. */
cmpl $28, %eax
ja L(less_4_till_page)
vmovd (%rdi), %xmm0
vmovd (%rsi), %xmm1
VPCMPEQ %xmm0, %xmmZERO, %xmm2
VPCMPEQ %xmm1, %xmm0, %xmm1
vpandn %xmm1, %xmm2, %xmm1
vpmovmskb %ymm1, %ecx
subl $0xf, %ecx
jnz L(check_ret_vec_page_cross)
# ifdef USE_AS_STRNCMP
cmpq $4, %rdx
jbe L(ret_zero_page_cross_slow_case1)
# endif
movl $28, %OFFSET_REG
/* Explicit check for 16 byte alignment. */
subl %eax, %OFFSET_REG
vmovd (%rdi, %OFFSET_REG64), %xmm0
vmovd (%rsi, %OFFSET_REG64), %xmm1
VPCMPEQ %xmm0, %xmmZERO, %xmm2
VPCMPEQ %xmm1, %xmm0, %xmm1
vpandn %xmm1, %xmm2, %xmm1
vpmovmskb %ymm1, %ecx
subl $0xf, %ecx
jnz L(check_ret_vec_page_cross)
# ifdef USE_AS_STRNCMP
addl $4, %OFFSET_REG
subq %OFFSET_REG64, %rdx
jbe L(ret_zero_page_cross_slow_case1)
subq $-(VEC_SIZE * 4), %rdx
leaq -(VEC_SIZE * 4)(%rdi, %OFFSET_REG64), %rdi
leaq -(VEC_SIZE * 4)(%rsi, %OFFSET_REG64), %rsi
# else
leaq (4 - VEC_SIZE * 4)(%rdi, %OFFSET_REG64), %rdi
leaq (4 - VEC_SIZE * 4)(%rsi, %OFFSET_REG64), %rsi
# endif
jmp L(prepare_loop_aligned)
# ifdef USE_AS_STRNCMP
.p2align 4,, 2
L(ret_zero_page_cross_slow_case1):
xorl %eax, %eax
ret
# endif
.p2align 4,, 10
L(less_4_till_page):
subq %rdi, %rsi
/* Extremely slow byte comparison loop. */
L(less_4_loop):
movzbl (%rdi), %eax
movzbl (%rsi, %rdi), %ecx
subl %ecx, %eax
jnz L(ret_less_4_loop)
testl %ecx, %ecx
jz L(ret_zero_4_loop)
# ifdef USE_AS_STRNCMP
decq %rdx
jz L(ret_zero_4_loop)
# endif
incq %rdi
/* end condition is reach page boundary (rdi is aligned). */
testl $31, %edi
jnz L(less_4_loop)
leaq -(VEC_SIZE * 4)(%rdi, %rsi), %rsi
addq $-(VEC_SIZE * 4), %rdi
# ifdef USE_AS_STRNCMP
subq $-(VEC_SIZE * 4), %rdx
# endif
jmp L(prepare_loop_aligned)
L(ret_zero_4_loop):
xorl %eax, %eax
ret
L(ret_less_4_loop):
xorl %r8d, %eax
subl %r8d, %eax
ret
# endif
END(STRCMP)
#endif
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