https://bugs.llvm.org/show_bug.cgi?id=42982
Bug ID: 42982
Summary: r368276 caused msan false positive in vectorized crc
code
Product: new-bugs
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: new bugs
Assignee: unassignedb...@nondot.org
Reporter: h...@chromium.org
CC: htmldevelo...@gmail.com, llvm-bugs@lists.llvm.org,
llvm-...@redking.me.uk
Created attachment 22372
--> https://bugs.llvm.org/attachment.cgi?id=22372&action=edit
reproducer
Building the attached source code at r368276:
$ /work/llvm.monorepo/build.release/bin/clang.bad crc32_simd.c -msse4.2
-mpclmul -g -O2 -fsanitize=memory
$ MSAN_SYMBOLIZER_PATH=/work/llvm.monorepo/build.release/bin/llvm-symbolizer
./a.out
==87075==WARNING: MemorySanitizer: use-of-uninitialized-value
#0 0x4a2c06 in crc32_sse42_simd_ /tmp/crc32_simd.c:141:10
#1 0x4a2c06 in main /tmp/crc32_simd.c:163:10
#2 0x7fed1ff0152a in __libc_start_main
(/lib/x86_64-linux-gnu/libc.so.6+0x2352a)
#3 0x41f299 in _start (/tmp/a.out+0x41f299)
SUMMARY: MemorySanitizer: use-of-uninitialized-value /tmp/crc32_simd.c:141:10
in crc32_sse42_simd_
Exiting
The warning didn't fire before, and I don't see anything wrong with the code.
This suggests perhaps the transformation in r368660 is not correct, or exposed
some previous problem. It was reverted in r368660.
(This was discovered in Chromium, see https://crbug.com/992853)
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