From: "H.J. Lu" <hjl.tools@gmail.com>
To: libc-alpha@sourceware.org
Cc: libc-stable@sourceware.org, Sunil K Pandey <skpgkp1@gmail.com>
Subject: [2.31/2.30/2.29] [PATCH] Fix avx2 strncmp offset compare condition check [BZ #25933]
Date: Sat, 4 Jul 2020 09:37:42 -0700 [thread overview]
Message-ID: <20200704163742.3347595-1-hjl.tools@gmail.com> (raw)
From: Sunil K Pandey <skpgkp1@gmail.com>
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)
---
sysdeps/x86_64/multiarch/strcmp-avx2.S | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/sysdeps/x86_64/multiarch/strcmp-avx2.S b/sysdeps/x86_64/multiarch/strcmp-avx2.S
index 48d03a9f46..ee82fa3e19 100644
--- a/sysdeps/x86_64/multiarch/strcmp-avx2.S
+++ b/sysdeps/x86_64/multiarch/strcmp-avx2.S
@@ -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. */
--
2.26.2
reply other threads:[~2020-07-04 16:37 UTC|newest]
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