[LLVMdev] Difficulty with reusing DAG nodes.

[Evan Cheng]

This isn't due to node reuse. Rather it's the scheduler complaining of  
a malformed DAG. You should dump out the DAG before scheduling and  
look for multiple use of a FLAG value.

Evan

On Sep 11, 2008, at 6:09 PM, Richard Pennington wrote:

> I'm trying to implement *MUL_LOHI for my processor.
>
> My processor has mulxss (e.g.) that gives the 32 high bits of a 64 bit
> multiply.
>
> I tried this in ios2ISelDAGToDAG.cpp:
>    /// Mul/Div with two results
>     case ISD::SMUL_LOHI:
>     case ISD::UMUL_LOHI: {
>       SDValue Op1 = Node->getOperand(0);
>       SDValue Op2 = Node->getOperand(1);
>       AddToISelQueue(Op1);
>       AddToISelQueue(Op2);
>
>       unsigned Op;
>       Op = (Opcode == ISD::UMUL_LOHI ? Nios2::MULxu : Nios2::MULx);
>       SDNode *Hi = CurDAG->getTargetNode(Op, MVT::Flag, Op1, Op2);
>       SDNode *Lo = CurDAG->getTargetNode(Nios2::MUL, MVT::Flag, Op1,  
> Op2);
>       if (!N.getValue(0).use_empty())
>         ReplaceUses(N.getValue(0), SDValue(Lo,0));
>       if (!N.getValue(1).use_empty())
>         ReplaceUses(N.getValue(1), SDValue(Hi,0));
>       return NULL;
>     }
>
> The code generator complains:
> nios2-elf-ecc:
> /home/rich/llvm-trunk-new/lib/CodeGen/SelectionDAG/ScheduleDAG.cpp: 
> 141:
> void llvm::ScheduleDAG::BuildSchedUnits(): Assertion `N->getNodeId()  
> ==
> -1 && "Node already inserted!"' failed
>
> I'm guessing that's because I'm reusing Op1 and Op2.
> What is the right way to reuse DAG operands?
>
> -Rich
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev