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glibc/sysdeps/x86_64/multiarch/strcmp-evex.S
Noah Goldstein e108c02a5e x86: Fix bug in strncmp-evex and strncmp-avx2 [BZ #28895] 
Logic can read before the start of `s1` / `s2` if both `s1` and `s2`
are near the start of a page. To avoid having the result contimated by
these comparisons the `strcmp` variants would mask off these
comparisons. This was missing in the `strncmp` variants causing
the bug. This commit adds the masking to `strncmp` so that out of
range comparisons don't affect the result.

test-strcmp, test-strncmp, test-wcscmp, and test-wcsncmp all pass as
well a full xcheck on x86_64 linux.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
2022-02-16 02:11:16 -06:00

1208 lines
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/* strcmp/wcscmp/strncmp/wcsncmp optimized with 256-bit EVEX instructions.
Copyright (C) 2021-2022 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_evex
# endif
# define PAGE_SIZE 4096
/* VEC_SIZE = Number of bytes in a ymm register. */
# define VEC_SIZE 32
# define CHAR_PER_VEC (VEC_SIZE / SIZE_OF_CHAR)
# define VMOVU vmovdqu64
# define VMOVA vmovdqa64
# ifdef USE_AS_WCSCMP
# define TESTEQ subl $0xff,
/* Compare packed dwords. */
# define VPCMP vpcmpd
# define VPMINU vpminud
# define VPTESTM vptestmd
/* 1 dword char == 4 bytes. */
# define SIZE_OF_CHAR 4
# else
# define TESTEQ incl
/* Compare packed bytes. */
# define VPCMP vpcmpb
# define VPMINU vpminub
# define VPTESTM vptestmb
/* 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
# if defined USE_AS_STRNCMP || defined USE_AS_WCSCMP
# define VEC_OFFSET 0
# else
# define VEC_OFFSET (-VEC_SIZE)
# endif
# define XMMZERO xmm16
# define XMM0 xmm17
# define XMM1 xmm18
# define YMMZERO ymm16
# define YMM0 ymm17
# define YMM1 ymm18
# define YMM2 ymm19
# define YMM3 ymm20
# define YMM4 ymm21
# define YMM5 ymm22
# define YMM6 ymm23
# define YMM7 ymm24
# define YMM8 ymm25
# define YMM9 ymm26
# define YMM10 ymm27
/* 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 256-bit
EVEX instructions consists of comparing (VPCMP) 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 5 EVEX instructions (3 VPCMP and 2
KORD). In general, the costs of comparing VEC_SIZE bytes (32-bytes)
are 3 VPCMP and 2 KORD instructions, together with VMOVU and ktestd
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 .text.evex, "ax", @progbits
ENTRY(STRCMP)
# ifdef USE_AS_STRNCMP
# ifdef __ILP32__
/* Clear the upper 32 bits. */
movl %edx, %edx
# 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)
# endif
movl %edi, %eax
orl %esi, %eax
/* Shift out the bits irrelivant to page boundary ([63:12]). */
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
VPTESTM %YMM0, %YMM0, %k2
/* Each bit cleared in K1 represents a mismatch or a null CHAR
in YMM0 and 32 bytes at (%rsi). */
VPCMP $0, (%rsi), %YMM0, %k1{%k2}
kmovd %k1, %ecx
# ifdef USE_AS_STRNCMP
cmpq $CHAR_PER_VEC, %rdx
jbe L(vec_0_test_len)
# endif
/* TESTEQ is `incl` for strcmp/strncmp and `subl $0xff` for
wcscmp/wcsncmp. */
/* All 1s represents all equals. TESTEQ will overflow to zero in
all equals case. Otherwise 1s will carry until position of first
mismatch. */
TESTEQ %ecx
jz L(more_3x_vec)
.p2align 4,, 4
L(return_vec_0):
tzcntl %ecx, %ecx
# ifdef USE_AS_WCSCMP
movl (%rdi, %rcx, SIZE_OF_CHAR), %edx
xorl %eax, %eax
cmpl (%rsi, %rcx, SIZE_OF_CHAR), %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):
ret
# ifdef USE_AS_STRNCMP
.p2align 4,, 4
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
ret
.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_evex
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_evex
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 its safe to subtract without
worrying about underflow. */
addq $-CHAR_PER_VEC, %rdx
cmpq %rcx, %rdx
jbe L(ret_zero)
# endif
# ifdef USE_AS_WCSCMP
movl VEC_SIZE(%rdi, %rcx, SIZE_OF_CHAR), %edx
xorl %eax, %eax
cmpl VEC_SIZE(%rsi, %rcx, SIZE_OF_CHAR), %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):
ret
.p2align 4,, 10
# ifdef USE_AS_STRNCMP
L(return_vec_3):
# if CHAR_PER_VEC <= 16
sall $CHAR_PER_VEC, %ecx
# else
salq $CHAR_PER_VEC, %rcx
# endif
# endif
L(return_vec_2):
# if (CHAR_PER_VEC <= 16) || !(defined USE_AS_STRNCMP)
tzcntl %ecx, %ecx
# else
tzcntq %rcx, %rcx
# endif
# ifdef USE_AS_STRNCMP
cmpq %rcx, %rdx
jbe L(ret_zero)
# endif
# ifdef USE_AS_WCSCMP
movl (VEC_SIZE * 2)(%rdi, %rcx, SIZE_OF_CHAR), %edx
xorl %eax, %eax
cmpl (VEC_SIZE * 2)(%rsi, %rcx, SIZE_OF_CHAR), %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):
ret
# ifndef USE_AS_STRNCMP
.p2align 4,, 10
L(return_vec_3):
tzcntl %ecx, %ecx
# ifdef USE_AS_WCSCMP
movl (VEC_SIZE * 3)(%rdi, %rcx, SIZE_OF_CHAR), %edx
xorl %eax, %eax
cmpl (VEC_SIZE * 3)(%rsi, %rcx, SIZE_OF_CHAR), %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):
ret
# endif
/* 32 byte align here ensures the main loop is ideally aligned
for DSB. */
.p2align 5
L(more_3x_vec):
/* Safe to compare 4x vectors. */
VMOVU (VEC_SIZE)(%rdi), %YMM0
VPTESTM %YMM0, %YMM0, %k2
VPCMP $0, (VEC_SIZE)(%rsi), %YMM0, %k1{%k2}
kmovd %k1, %ecx
TESTEQ %ecx
jnz L(return_vec_1)
# ifdef USE_AS_STRNCMP
subq $(CHAR_PER_VEC * 2), %rdx
jbe L(ret_zero)
# endif
VMOVU (VEC_SIZE * 2)(%rdi), %YMM0
VPTESTM %YMM0, %YMM0, %k2
VPCMP $0, (VEC_SIZE * 2)(%rsi), %YMM0, %k1{%k2}
kmovd %k1, %ecx
TESTEQ %ecx
jnz L(return_vec_2)
VMOVU (VEC_SIZE * 3)(%rdi), %YMM0
VPTESTM %YMM0, %YMM0, %k2
VPCMP $0, (VEC_SIZE * 3)(%rsi), %YMM0, %k1{%k2}
kmovd %k1, %ecx
TESTEQ %ecx
jnz L(return_vec_3)
# ifdef USE_AS_STRNCMP
cmpq $(CHAR_PER_VEC * 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
# ifdef USE_AS_WCSCMP
L(prepare_loop_no_len):
movl %edi, %ecx
andl $(VEC_SIZE * 4 - 1), %ecx
shrl $2, %ecx
leaq (CHAR_PER_VEC * 2)(%rdx, %rcx), %rdx
# else
/* Store N + (VEC_SIZE * 4) and place check at the begining of
the loop. */
leaq (VEC_SIZE * 2)(%rdi, %rdx), %rdx
L(prepare_loop_no_len):
# endif
# else
L(prepare_loop_no_len):
# endif
/* Align s1 and adjust s2 accordingly. */
subq %rdi, %rsi
andq $-(VEC_SIZE * 4), %rdi
L(prepare_loop_readj):
addq %rdi, %rsi
# if (defined USE_AS_STRNCMP) && !(defined USE_AS_WCSCMP)
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
vpxorq %YMMZERO, %YMMZERO, %YMMZERO
/* Loop 4x comparisons at a time. */
.p2align 4
L(loop):
/* End condition for strncmp. */
# ifdef USE_AS_STRNCMP
subq $(CHAR_PER_VEC * 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
VPMINU %YMM0, %YMM2, %YMM8
VPMINU %YMM4, %YMM6, %YMM9
/* A zero CHAR in YMM9 means that there is a null CHAR. */
VPMINU %YMM8, %YMM9, %YMM9
/* Each bit set in K1 represents a non-null CHAR in YMM8. */
VPTESTM %YMM9, %YMM9, %k1
vpxorq (VEC_SIZE * 0)(%rsi), %YMM0, %YMM1
vpxorq (VEC_SIZE * 1)(%rsi), %YMM2, %YMM3
vpxorq (VEC_SIZE * 2)(%rsi), %YMM4, %YMM5
/* Ternary logic to xor (VEC_SIZE * 3)(%rsi) with YMM6 while
oring with YMM1. Result is stored in YMM6. */
vpternlogd $0xde, (VEC_SIZE * 3)(%rsi), %YMM1, %YMM6
/* Or together YMM3, YMM5, and YMM6. */
vpternlogd $0xfe, %YMM3, %YMM5, %YMM6
/* A non-zero CHAR in YMM6 represents a mismatch. */
VPCMP $0, %YMMZERO, %YMM6, %k0{%k1}
kmovd %k0, %LOOP_REG
TESTEQ %LOOP_REG
jz L(loop)
/* Find which VEC has the mismatch of end of string. */
VPTESTM %YMM0, %YMM0, %k1
VPCMP $0, %YMMZERO, %YMM1, %k0{%k1}
kmovd %k0, %ecx
TESTEQ %ecx
jnz L(return_vec_0_end)
VPTESTM %YMM2, %YMM2, %k1
VPCMP $0, %YMMZERO, %YMM3, %k0{%k1}
kmovd %k0, %ecx
TESTEQ %ecx
jnz L(return_vec_1_end)
/* Handle VEC 2 and 3 without branches. */
L(return_vec_2_3_end):
# ifdef USE_AS_STRNCMP
subq $(CHAR_PER_VEC * 2), %rdx
jbe L(ret_zero_end)
# endif
VPTESTM %YMM4, %YMM4, %k1
VPCMP $0, %YMMZERO, %YMM5, %k0{%k1}
kmovd %k0, %ecx
TESTEQ %ecx
# if CHAR_PER_VEC <= 16
sall $CHAR_PER_VEC, %LOOP_REG
orl %ecx, %LOOP_REG
# else
salq $CHAR_PER_VEC, %LOOP_REG64
orq %rcx, %LOOP_REG64
# endif
L(return_vec_3_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. */
# if CHAR_PER_VEC <= 16
tzcntl %LOOP_REG, %LOOP_REG
# else
tzcntq %LOOP_REG64, %LOOP_REG64
# endif
# ifdef USE_AS_STRNCMP
cmpq %LOOP_REG64, %rdx
jbe L(ret_zero_end)
# endif
# ifdef USE_AS_WCSCMP
movl (VEC_SIZE * 2)(%rdi, %LOOP_REG64, SIZE_OF_CHAR), %ecx
xorl %eax, %eax
cmpl (VEC_SIZE * 2)(%rsi, %LOOP_REG64, SIZE_OF_CHAR), %ecx
je L(ret5)
setl %al
negl %eax
xorl %r8d, %eax
# else
movzbl (VEC_SIZE * 2)(%rdi, %LOOP_REG64), %eax
movzbl (VEC_SIZE * 2)(%rsi, %LOOP_REG64), %ecx
subl %ecx, %eax
xorl %r8d, %eax
subl %r8d, %eax
# endif
L(ret5):
ret
# ifdef USE_AS_STRNCMP
.p2align 4,, 2
L(ret_zero_end):
xorl %eax, %eax
ret
# 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):
# if CHAR_PER_VEC <= 16
sall $CHAR_PER_VEC, %ecx
# else
salq $CHAR_PER_VEC, %rcx
# endif
# endif
L(return_vec_0_end):
# if (CHAR_PER_VEC <= 16) || !(defined USE_AS_STRNCMP)
tzcntl %ecx, %ecx
# else
tzcntq %rcx, %rcx
# endif
# ifdef USE_AS_STRNCMP
cmpq %rcx, %rdx
jbe L(ret_zero_end)
# endif
# ifdef USE_AS_WCSCMP
movl (%rdi, %rcx, SIZE_OF_CHAR), %edx
xorl %eax, %eax
cmpl (%rsi, %rcx, SIZE_OF_CHAR), %edx
je L(ret6)
setl %al
negl %eax
/* This is the non-zero case for `eax` so just xorl with `r8d`
flip is `rdi` and `rsi` where swapped. */
xorl %r8d, %eax
# else
movzbl (%rdi, %rcx), %eax
movzbl (%rsi, %rcx), %ecx
subl %ecx, %eax
/* Flip `eax` if `rdi` and `rsi` where swapped in page cross
logic. Subtract `r8d` after xor for zero case. */
xorl %r8d, %eax
subl %r8d, %eax
# endif
L(ret6):
ret
# ifndef USE_AS_STRNCMP
.p2align 4,, 10
L(return_vec_1_end):
tzcntl %ecx, %ecx
# ifdef USE_AS_WCSCMP
movl VEC_SIZE(%rdi, %rcx, SIZE_OF_CHAR), %edx
xorl %eax, %eax
cmpl VEC_SIZE(%rsi, %rcx, SIZE_OF_CHAR), %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):
ret
# endif
/* 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 in which 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
VPTESTM %YMM0, %YMM0, %k2
VPCMP $0, (%rsi), %YMM0, %k1{%k2}
kmovd %k1, %ecx
TESTEQ %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
VPTESTM %YMM0, %YMM0, %k2
VPCMP $0, -VEC_SIZE(%rsi, %rax), %YMM0, %k1{%k2}
/* Mask of potentially valid bits. The lower bits can be out of
range comparisons (but safe regarding page crosses). */
# ifdef USE_AS_WCSCMP
movl $-1, %r10d
movl %esi, %ecx
andl $(VEC_SIZE - 1), %ecx
shrl $2, %ecx
shlxl %ecx, %r10d, %ecx
movzbl %cl, %r10d
# else
movl $-1, %ecx
shlxl %esi, %ecx, %r10d
# endif
kmovd %k1, %ecx
notl %ecx
# ifdef USE_AS_STRNCMP
# ifdef USE_AS_WCSCMP
movl %eax, %r11d
shrl $2, %r11d
cmpq %r11, %rdx
# else
cmpq %rax, %rdx
# endif
jbe L(return_page_cross_end_check)
# endif
movl %eax, %OFFSET_REG
/* Readjust eax before potentially returning to the loop. */
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
# if (defined USE_AS_STRNCMP) || (defined USE_AS_WCSCMP)
leal -VEC_SIZE(%OFFSET_REG64, %rcx, SIZE_OF_CHAR), %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):
ret
# ifdef USE_AS_STRNCMP
.p2align 4,, 10
L(return_page_cross_end_check):
andl %r10d, %ecx
tzcntl %ecx, %ecx
leal -VEC_SIZE(%rax, %rcx, SIZE_OF_CHAR), %ecx
# ifdef USE_AS_WCSCMP
sall $2, %edx
# endif
cmpl %ecx, %edx
ja L(return_page_cross_cmp_mem)
xorl %eax, %eax
ret
# 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. */
VMOVA VEC_SIZE(%rdi), %YMM0
VPTESTM %YMM0, %YMM0, %k2
VPCMP $0, VEC_SIZE(%rsi), %YMM0, %k1{%k2}
kmovd %k1, %ecx
TESTEQ %ecx
jnz L(return_vec_1_end)
# ifdef USE_AS_STRNCMP
cmpq $(CHAR_PER_VEC * 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
VPTESTM %YMM0, %YMM0, %k2
VPCMP $0, -(VEC_SIZE * 2)(%rsi, %rax), %YMM0, %k1{%k2}
kmovd %k1, %ecx
TESTEQ %ecx
jnz L(return_vec_page_cross_0)
VMOVU -(VEC_SIZE * 1)(%rdi, %rax), %YMM0
VPTESTM %YMM0, %YMM0, %k2
VPCMP $0, -(VEC_SIZE * 1)(%rsi, %rax), %YMM0, %k1{%k2}
kmovd %k1, %ecx
TESTEQ %ecx
jnz L(return_vec_page_cross_1)
# ifdef USE_AS_STRNCMP
/* Must check length here as length might proclude reading next
page. */
# ifdef USE_AS_WCSCMP
movl %eax, %r11d
shrl $2, %r11d
cmpq %r11, %rdx
# else
cmpq %rax, %rdx
# endif
jbe L(ret_zero_in_loop_page_cross)
# endif
/* Finish the loop. */
VMOVA (VEC_SIZE * 2)(%rdi), %YMM4
VMOVA (VEC_SIZE * 3)(%rdi), %YMM6
VPMINU %YMM4, %YMM6, %YMM9
VPTESTM %YMM9, %YMM9, %k1
vpxorq (VEC_SIZE * 2)(%rsi), %YMM4, %YMM5
/* YMM6 = YMM5 | ((VEC_SIZE * 3)(%rsi) ^ YMM6). */
vpternlogd $0xde, (VEC_SIZE * 3)(%rsi), %YMM5, %YMM6
VPCMP $0, %YMMZERO, %YMM6, %k0{%k1}
kmovd %k0, %LOOP_REG
TESTEQ %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 $(CHAR_PER_VEC * 4), %rdx
ja L(loop_skip_page_cross_check)
L(ret_zero_in_loop_page_cross):
xorl %eax, %eax
ret
# 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
# if defined USE_AS_STRNCMP || defined USE_AS_WCSCMP
leal -VEC_SIZE(%rax, %rcx, SIZE_OF_CHAR), %ecx
# ifdef USE_AS_STRNCMP
# ifdef USE_AS_WCSCMP
/* Must divide ecx instead of multiply rdx due to overflow. */
movl %ecx, %eax
shrl $2, %eax
cmpq %rax, %rdx
# else
cmpq %rcx, %rdx
# endif
jbe L(ret_zero_in_loop_page_cross)
# endif
# 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):
ret
.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,, 8
L(page_cross_loop):
VMOVU (%rdi, %OFFSET_REG64, SIZE_OF_CHAR), %YMM0
VPTESTM %YMM0, %YMM0, %k2
VPCMP $0, (%rsi, %OFFSET_REG64, SIZE_OF_CHAR), %YMM0, %k1{%k2}
kmovd %k1, %ecx
TESTEQ %ecx
jnz L(check_ret_vec_page_cross)
addl $CHAR_PER_VEC, %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)
# ifdef USE_AS_WCSCMP
shrl $2, %eax
# endif
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, SIZE_OF_CHAR), %YMM0
VPTESTM %YMM0, %YMM0, %k2
VPCMP $0, (%rsi, %OFFSET_REG64, SIZE_OF_CHAR), %YMM0, %k1{%k2}
kmovd %k1, %ecx
# ifdef USE_AS_STRNCMP
leal CHAR_PER_VEC(%OFFSET_REG64), %eax
cmpq %rax, %rdx
jbe L(check_ret_vec_page_cross2)
# ifdef USE_AS_WCSCMP
addq $-(CHAR_PER_VEC * 2), %rdx
# else
addq %rdi, %rdx
# endif
# endif
TESTEQ %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, SIZE_OF_CHAR), %edx
xorl %eax, %eax
cmpl (%rsi, %rcx, SIZE_OF_CHAR), %edx
je L(ret12)
setl %al
negl %eax
xorl %r8d, %eax
# else
movzbl (%rdi, %rcx, SIZE_OF_CHAR), %eax
movzbl (%rsi, %rcx, SIZE_OF_CHAR), %ecx
subl %ecx, %eax
xorl %r8d, %eax
subl %r8d, %eax
# endif
L(ret12):
ret
# ifdef USE_AS_STRNCMP
.p2align 4,, 10
L(check_ret_vec_page_cross2):
TESTEQ %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
ret
# 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):
# ifdef USE_AS_WCSCMP
shrl $2, %eax
# endif
/* Find largest load size we can use. */
cmpl $(16 / SIZE_OF_CHAR), %eax
ja L(less_16_till_page)
/* Use 16 byte comparison. */
vmovdqu (%rdi), %xmm0
VPTESTM %xmm0, %xmm0, %k2
VPCMP $0, (%rsi), %xmm0, %k1{%k2}
kmovd %k1, %ecx
# ifdef USE_AS_WCSCMP
subl $0xf, %ecx
# else
incw %cx
# endif
jnz L(check_ret_vec_page_cross)
movl $(16 / SIZE_OF_CHAR), %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
vmovdqu (%rdi, %OFFSET_REG64, SIZE_OF_CHAR), %xmm0
VPTESTM %xmm0, %xmm0, %k2
VPCMP $0, (%rsi, %OFFSET_REG64, SIZE_OF_CHAR), %xmm0, %k1{%k2}
kmovd %k1, %ecx
# ifdef USE_AS_WCSCMP
subl $0xf, %ecx
# else
incw %cx
# endif
jnz L(check_ret_vec_page_cross)
# ifdef USE_AS_STRNCMP
addl $(16 / SIZE_OF_CHAR), %OFFSET_REG
subq %OFFSET_REG64, %rdx
jbe L(ret_zero_page_cross_slow_case0)
subq $-(CHAR_PER_VEC * 4), %rdx
leaq -(VEC_SIZE * 4)(%rdi, %OFFSET_REG64, SIZE_OF_CHAR), %rdi
leaq -(VEC_SIZE * 4)(%rsi, %OFFSET_REG64, SIZE_OF_CHAR), %rsi
# else
leaq (16 - VEC_SIZE * 4)(%rdi, %OFFSET_REG64, SIZE_OF_CHAR), %rdi
leaq (16 - VEC_SIZE * 4)(%rsi, %OFFSET_REG64, SIZE_OF_CHAR), %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):
cmpl $(24 / SIZE_OF_CHAR), %eax
ja L(less_8_till_page)
/* Use 8 byte comparison. */
vmovq (%rdi), %xmm0
vmovq (%rsi), %xmm1
VPTESTM %xmm0, %xmm0, %k2
VPCMP $0, %xmm1, %xmm0, %k1{%k2}
kmovd %k1, %ecx
# ifdef USE_AS_WCSCMP
subl $0x3, %ecx
# else
incb %cl
# endif
jnz L(check_ret_vec_page_cross)
# ifdef USE_AS_STRNCMP
cmpq $(8 / SIZE_OF_CHAR), %rdx
jbe L(ret_zero_page_cross_slow_case0)
# endif
movl $(24 / SIZE_OF_CHAR), %OFFSET_REG
subl %eax, %OFFSET_REG
vmovq (%rdi, %OFFSET_REG64, SIZE_OF_CHAR), %xmm0
vmovq (%rsi, %OFFSET_REG64, SIZE_OF_CHAR), %xmm1
VPTESTM %xmm0, %xmm0, %k2
VPCMP $0, %xmm1, %xmm0, %k1{%k2}
kmovd %k1, %ecx
# ifdef USE_AS_WCSCMP
subl $0x3, %ecx
# else
incb %cl
# endif
jnz L(check_ret_vec_page_cross)
# ifdef USE_AS_STRNCMP
addl $(8 / SIZE_OF_CHAR), %OFFSET_REG
subq %OFFSET_REG64, %rdx
jbe L(ret_zero_page_cross_slow_case0)
subq $-(CHAR_PER_VEC * 4), %rdx
leaq -(VEC_SIZE * 4)(%rdi, %OFFSET_REG64, SIZE_OF_CHAR), %rdi
leaq -(VEC_SIZE * 4)(%rsi, %OFFSET_REG64, SIZE_OF_CHAR), %rsi
# else
leaq (8 - VEC_SIZE * 4)(%rdi, %OFFSET_REG64, SIZE_OF_CHAR), %rdi
leaq (8 - VEC_SIZE * 4)(%rsi, %OFFSET_REG64, SIZE_OF_CHAR), %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 $-(CHAR_PER_VEC * 2), %rdx
/* We already checked for len <= 1 so cannot hit that case here.
*/
# endif
testl %eax, %eax
jnz L(prepare_loop)
ret
.p2align 4,, 8
L(ret_less_8_wcs):
setl %OFFSET_REG8
negl %OFFSET_REG
movl %OFFSET_REG, %eax
xorl %r8d, %eax
ret
# else
cmpl $28, %eax
ja L(less_4_till_page)
vmovd (%rdi), %xmm0
vmovd (%rsi), %xmm1
VPTESTM %xmm0, %xmm0, %k2
VPCMP $0, %xmm1, %xmm0, %k1{%k2}
kmovd %k1, %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 / SIZE_OF_CHAR), %OFFSET_REG
subl %eax, %OFFSET_REG
vmovd (%rdi, %OFFSET_REG64, SIZE_OF_CHAR), %xmm0
vmovd (%rsi, %OFFSET_REG64, SIZE_OF_CHAR), %xmm1
VPTESTM %xmm0, %xmm0, %k2
VPCMP $0, %xmm1, %xmm0, %k1{%k2}
kmovd %k1, %ecx
subl $0xf, %ecx
jnz L(check_ret_vec_page_cross)
# ifdef USE_AS_STRNCMP
addl $(4 / SIZE_OF_CHAR), %OFFSET_REG
subq %OFFSET_REG64, %rdx
jbe L(ret_zero_page_cross_slow_case1)
subq $-(CHAR_PER_VEC * 4), %rdx
leaq -(VEC_SIZE * 4)(%rdi, %OFFSET_REG64, SIZE_OF_CHAR), %rdi
leaq -(VEC_SIZE * 4)(%rsi, %OFFSET_REG64, SIZE_OF_CHAR), %rsi
# else
leaq (4 - VEC_SIZE * 4)(%rdi, %OFFSET_REG64, SIZE_OF_CHAR), %rdi
leaq (4 - VEC_SIZE * 4)(%rsi, %OFFSET_REG64, SIZE_OF_CHAR), %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 $-(CHAR_PER_VEC * 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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