[LLVMbugs] [Bug 16460] New: instcombine miscompile (t12958 case from PR16431)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=16460

            Bug ID: 16460
           Summary: instcombine miscompile (t12958 case from PR16431)
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: hfinkel at anl.gov
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 10770
  --> http://llvm.org/bugs/attachment.cgi?id=10770&action=edit
bugpoint reduced test case and input file

instcombine miscompiles the attached input (there is an input text file read by
the program which demonstrates the problem). This is the t12958 case from
PR16431.

Specifically, if you run:
opt -instcombine bugpoint-passinput.ll

Then the resulting program segmentation faults.

whereas compiling it without running instcombine, the resulting program
outputs:
res = 4294930716

Unfortunately, bugpoint crashes when attempting to further reduce the test case
:(
 -- but at least it was able to isolate the relevant pass.

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