[llvm-bugs] [Bug 36184] New: Regression: Segfault in LICM after upgrading to 6.0.0

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=36184

            Bug ID: 36184
           Summary: Regression: Segfault in LICM after upgrading to 6.0.0
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: alex at crichton.co
                CC: llvm-bugs at lists.llvm.org

Created attachment 19788
  --> https://bugs.llvm.org/attachment.cgi?id=19788&action=edit
crashing bytecode

We've *almost* upgraded to LLVM 6 in rust-lang/rust [1] but we seem to have hit
what is hopefully our last blocker, a segfault when optimizing IR on MSVC. The
attached IR will non-deterministically segfault in `opt` during the LICM
passes. I've reproduced this with:

    for i in `seq 1 1000`; do
        echo $i
        opt -O2 -o /dev/null foo.ll || break
    done

Sometimes it takes up to 100 runs to crash, but I've been able to crash on a
debug and a release build of LLVM, both on Linux and on Windows.

[1]: https://github.com/rust-lang/rust/pull/47828

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