[LLVMbugs] [Bug 17876] New: TailDuplicate makes bad assumption about SSA form

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Mon Nov 11 07:09:40 PST 2013


            Bug ID: 17876
           Summary: TailDuplicate makes bad assumption about SSA form
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: justin.holewinski at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 11508
  --> http://llvm.org/bugs/attachment.cgi?id=11508&action=edit
Repro for TailDuplicate assert failure

During late machine code optimization with NVPTX, the following code in
TailDuplicate.cpp may be hit:

236├>      MachineInstr *DefMI = MRI->getVRegDef(VReg);

MachineRegisterInfo::getVRegDef() assumes SSA form, but when running
TailDuplicate MRI->isSSA() is false.

For repro, the attached .ll file can be used with the nvptx target with the
following change to NVPTXTargetMachine.cpp:

1. Remove "disablePass(&TailDuplicateID);"

The TailDuplicate pass is currently disabled in NVPTX for a few reasons,
including this one.

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