[LLVMbugs] [Bug 15787] New: Assert in llvm::MachineRegisterInfo::clearVirtRegs: Vreg use list non-empty still

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=15787

            Bug ID: 15787
           Summary: Assert in llvm::MachineRegisterInfo::clearVirtRegs:
                    Vreg use list non-empty still
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: hfinkel at anl.gov
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 10373
  --> http://llvm.org/bugs/attachment.cgi?id=10373&action=edit
bugpoint reduced test case

I may have found a bug in the register allocator. To see the bug, first apply
the attached patch (which makes the PPC optimizeCompareInst function more
aggressive than it should be), and then run the attached test case using:
-mtriple=powerpc64-unknown-linux-gnu -mcpu=pwr7 -- While applying the patch
will make optimizeCompareInst make a transformation that it can't guarantee is
legal, I don't think that the register allocator should care about that.

It currently asserts like this:
llc: llvm-trunk/lib/CodeGen/MachineRegisterInfo.cpp:111: void
llvm::MachineRegisterInfo::clearVirtRegs(): Assertion
`VRegInfo[TargetRegisterInfo::index2VirtReg(i)].second == 0 && "Vreg use list
non-empty still?"' failed.

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