[LLVMbugs] [Bug 4093] New: LegalizeDAG does not allow expansion of subtraction operation

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=4093

           Summary: LegalizeDAG does not allow expansion of subtraction
                    operation
           Product: libraries
           Version: 2.5
          Platform: PC
        OS/Version: Windows NT
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Common Code Generator Code
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: micah.villmow at amd.com
                CC: llvmbugs at cs.uiuc.edu


I ran into a problem where setOperationAction(ISD::SUB, MVT::i64, Expand) was
giving an assertion.

I wrote this code to expand subtraction into multiple instructions.

It goes at line 3352 of LegalizeDAG.cpp.

if (Node->getOpcode() == ISD::SUB &&
        TLI.isOperationLegalOrCustom(ISD::ADD, VT)) {
                if (VT.isFloatingPoint() &&
                        TLI.isOperationLegalOrCustom(ISD::MUL, VT)) {
                SDValue t1 = SDValue(DAG.getNode(ISD::MUL, dl,
                                                 VT, Tmp2,
DAG.getConstantFP(-1, VT)
                                                 ).getNode(), 0);
                Result = SDValue(DAG.getNode(ISD::ADD, dl, VT, Tmp1, 
                                                 t1).getNode(), 0);
                break;
                } else if (VT.isInteger() &&
                        TLI.isOperationLegalOrCustom(ISD::XOR, VT)) {           
                SDValue t1 = SDValue(DAG.getNode(ISD::XOR, dl,
                                                 VT, Tmp2,DAG.getConstant(
                                                 (uint64_t)-1, VT)
                                                 ).getNode(), 0);               
                SDValue t2 = SDValue(DAG.getNode(ISD::ADD, dl,
                                                 VT, t1, DAG.getConstant(1, VT)
                                                 ).getNode(), 0);               
                Result = SDValue(DAG.getNode(ISD::ADD, dl, VT, Tmp1, 
                                                 t2).getNode(), 0);
                break;
                }
          }


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