[llvm-commits] [llvm] r62383 - in /llvm/trunk: lib/CodeGen/SelectionDAG/DAGCombiner.cpp test/CodeGen/X86/scalar-extract.ll

[Duncan Sands]

Hi Mon Ping,

> +  SDValue InVec = N->getOperand(0);
> +  SDValue EltNo = N->getOperand(1);
> +
> +  if (isa<ConstantSDNode>(EltNo)) {
> +    unsigned Elt = cast<ConstantSDNode>(EltNo)->getZExtValue();
> +    if (InVec.getOpcode() == ISD::SCALAR_TO_VECTOR && Elt == 0) {
> +      return InVec.getOperand(0);
> +    }
> +  }

I don't think you need to check EltNo at all: if it's not the first
element then the value is undefined, i.e. you can assume it is whatever
is convenient to you.  In particular you may assume that it is the same
as the first element.  In short: if the input is SCALAR_TO_VECTOR, you
can always return InVec.getOperand(0) regardless of EltNo.

Ciao,

Duncan.