[llvm-bugs] [Bug 44652] New: eb0e1978df7b9e7 caused msan false positive in vectorized crc code

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=44652

            Bug ID: 44652
           Summary: eb0e1978df7b9e7 caused msan false positive in
                    vectorized crc code
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: nicolasweber at gmx.de
                CC: llvm-bugs at lists.llvm.org

Created attachment 23056
  --> https://bugs.llvm.org/attachment.cgi?id=23056&action=edit
crc_folding.c standalone repro

This is very similar to issue 42982, but in slightly different vectorized crc
code in zlib.

As far as I can tell, no uninitialized reads happen here, and things are happy
before eb0e1978df7b9e7

bin/clang crc_folding.c -msse4.2 -mpclmul -g -O2 -fsanitize=memory && ./a.out 
==135688==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x499549 in crc_fold_512to32
/usr/local/google/home/thakis/src/chrome/src/crc_folding.c:479:16
    #1 0x499549 in main
/usr/local/google/home/thakis/src/chrome/src/crc_folding.c:514:10
    #2 0x7f706ab6f52a in __libc_start_main
(/lib/x86_64-linux-gnu/libc.so.6+0x2352a)
    #3 0x41f269 in _start
(/usr/local/google/home/thakis/src/chrome/src/a.out+0x41f269)

SUMMARY: MemorySanitizer: use-of-uninitialized-value
/usr/local/google/home/thakis/src/chrome/src/crc_folding.c:479:16 in
crc_fold_512to32


(reduced from https://crbug.com/1045291)

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