llvm dev - Dec 2009 - [LLVMdev] LegalizeDAG Error?

The LegalizeDAG.cpp file has this code in SelectionDAGLegalize::PromoteNode:

  case ISD::BSWAP: {
    unsigned DiffBits = NVT.getSizeInBits() - OVT.getSizeInBits();
    Tmp1 = DAG.getNode(ISD::ZERO_EXTEND, dl, NVT, Tmp1);
    Tmp1 = DAG.getNode(ISD::BSWAP, dl, NVT, Tmp1);
    Tmp1 = DAG.getNode(ISD::SRL, dl, NVT, Tmp1,
                       DAG.getConstant(DiffBits, TLI.getShiftAmountTy()));
    Results.push_back(Tmp1);
    break;
  }

Notice the first DAG.getNode() call. It's using "Tmp1", which at
this point isn't initialized. What should it be instead?

-bw

On Dec 22, 2009, at 2:38 PMPST, Bill Wendling wrote:
> The LegalizeDAG.cpp file has this code in  
> SelectionDAGLegalize::PromoteNode:
>
>  case ISD::BSWAP: {
>    unsigned DiffBits = NVT.getSizeInBits() - OVT.getSizeInBits();
>    Tmp1 = DAG.getNode(ISD::ZERO_EXTEND, dl, NVT, Tmp1);
>    Tmp1 = DAG.getNode(ISD::BSWAP, dl, NVT, Tmp1);
>    Tmp1 = DAG.getNode(ISD::SRL, dl, NVT, Tmp1,
>                       DAG.getConstant(DiffBits,  
> TLI.getShiftAmountTy()));
>    Results.push_back(Tmp1);
>    break;
>  }
>
> Notice the first DAG.getNode() call. It's using "Tmp1", which
at
> this point isn't initialized. What should it be instead?
Node->getOperand(0) , probably, try it.  Nice catch.

On Dec 22, 2009, at 2:46 PM, Dale Johannesen wrote:
> On Dec 22, 2009, at 2:38 PMPST, Bill Wendling wrote:
> 
>> The LegalizeDAG.cpp file has this code in
SelectionDAGLegalize::PromoteNode:
>> 
>> case ISD::BSWAP: {
>>   unsigned DiffBits = NVT.getSizeInBits() - OVT.getSizeInBits();
>>   Tmp1 = DAG.getNode(ISD::ZERO_EXTEND, dl, NVT, Tmp1);
>>   Tmp1 = DAG.getNode(ISD::BSWAP, dl, NVT, Tmp1);
>>   Tmp1 = DAG.getNode(ISD::SRL, dl, NVT, Tmp1,
>>                      DAG.getConstant(DiffBits,
TLI.getShiftAmountTy()));
>>   Results.push_back(Tmp1);
>>   break;
>> }
>> 
>> Notice the first DAG.getNode() call. It's using "Tmp1",
which at this point isn't initialized. What should it be instead?
> 
> Node->getOperand(0) , probably, try it.  Nice catch.
> 
Sounds reasonable to me. I'll check in the change. :-)

Thanks

-bw