[llvm-bugs] [Bug 28828] New: Loop unrolling lead to program crash

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=28828

            Bug ID: 28828
           Summary: Loop unrolling lead to program crash
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Loop Optimizer
          Assignee: unassignedbugs at nondot.org
          Reporter: feishenniubi at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Created attachment 16869
  --> https://llvm.org/bugs/attachment.cgi?id=16869&action=edit
The original program, in .ll form

Running the trunk version of the loop unroller will transform a non-crashing
program into a crashing one.

Here's how the original program behaves:
> llc test.ll -o test.s
> g++ test.s -o test
> ./test
// Program terminates normally

Here's how the loop-unrolled program behaves:
> opt test.ll -loop-unroll -o test_opt.bc
> llc test_opt.bc -o test_opt.s
> g++ test_opt.s -o test_opt
> ./test_opt
// Segmentation fault

I can reproduce the issue on two different Linux platforms: RHEL 7.2 and Ubuntu
14.04. Both platform use gcc 5.3 toolchain.

Also, I am not able to shrink the test case further using bugpoint due to an
unfixed bug in bugpoint itself: https://llvm.org/bugs/show_bug.cgi?id=28803

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