[llvm-bugs] [Bug 33706] New: [Loop vectorizer] miscompile since r272715

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https://bugs.llvm.org/show_bug.cgi?id=33706

            Bug ID: 33706
           Summary: [Loop vectorizer] miscompile since r272715
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Loop Optimizer
          Assignee: unassignedbugs at nondot.org
          Reporter: Wolfgang_Pieb at playstation.sony.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 18763
  --> https://bugs.llvm.org/attachment.cgi?id=18763&action=edit
test case (different output with -O2 vs. -O0).

The attached test case produces different output for -O2 vs. -O0 compilation,
which we bisected down to the loop vectorizer. The failure started with
r272715, but appears to be masked whenever the GVNHoist pass is enabled (which
it currently isn't at r307289).

Apologies for not providing a more narrowed test case with opt/llc, but opt
resisted my attempts to find a set of switches that reproduces the failure. 

Compile with

clang -O2 --target=x86_64-unknown-linux-gnu

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