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Fix avx2 strncmp offset compare condition check [BZ #25933] 

strcmp-avx2.S: In avx2 strncmp function, strings are compared in
chunks of 4 vector size(i.e. 32x4=128 byte for avx2). After first 4
vector size comparison, code must check whether it already passed
the given offset. This patch implement avx2 offset check condition
for strncmp function, if both string compare same for first 4 vector
size.

(cherry picked from commit 75870237ff3bb363447b03f4b0af100227570910)
This commit is contained in:
Sunil K Pandey 2020-06-12 08:57:16 -07:00 committed by H.J. Lu
parent b0d3f7858c
commit 0a4d3eac67
1 changed files with 15 additions and 0 deletions
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15
sysdeps/x86_64/multiarch/strcmp-avx2.S
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@ -591,7 +591,14 @@ L(loop_cross_page_2_vec):
movl $(PAGE_SIZE / (VEC_SIZE * 4) - 1), %esi
testq %rdi, %rdi
# ifdef USE_AS_STRNCMP
/* At this point, if %rdi value is 0, it already tested
VEC_SIZE*4+%r10 byte starting from %rax. This label
checks whether strncmp maximum offset reached or not. */
je L(string_nbyte_offset_check)
# else
je L(back_to_loop)
# endif
tzcntq %rdi, %rcx
addq %r10, %rcx
/* Adjust for number of bytes skipped. */
@ -627,6 +634,14 @@ L(loop_cross_page_2_vec):
VZEROUPPER
ret
# ifdef USE_AS_STRNCMP
L(string_nbyte_offset_check):
leaq (VEC_SIZE * 4)(%r10), %r10
cmpq %r10, %r11
jbe L(zero)
jmp L(back_to_loop)
# endif
.p2align 4
L(cross_page_loop):
/* Check one byte/dword at a time. */