[LLVMbugs] [Bug 1951] New: Gratuitous renames of variables

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=1951

           Summary: Gratuitous renames of variables
           Product: tools
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: TableGen
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: scottm at aero.org
                CC: llvmbugs at cs.uiuc.edu


Ran across this unique problem in tblgen in the CellSPU development. Note the
"Tmp2" variable reference in the code:

SDNode *Emit_0(const SDOperand &N, unsigned Opc0, unsigned Opc1, MVT::ValueType
VT0, MVT::ValueType VT1) DISABLE_INLINE {
  SDOperand N0 = N.getOperand(0);
  SDOperand N00 = N0.getOperand(0);
  SDOperand N01 = N0.getOperand(1);
  SDOperand N1 = N.getOperand(1);
  SDOperand N10 = N1.getOperand(0);
  SDOperand N11 = N1.getOperand(1);
  SDOperand Tmp3(CurDAG->getTargetNode(Opc0, VT0, N00), 0);
  return CurDAG->SelectNodeTo(N.Val, Opc1, VT1, Tmp3, Tmp2);
}

I did manage to run this bug to ground -- tblgen was gratuitously renaming
variables when no temporary was produced. Test case also attached as is a
patch.


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