Lowering instructions

In this chapter, we will see the implementation of 3 things – Function call calling convention, Formal argument calling convention, and Return value calling convention. We create a file TOYISelLowering.cpp, and implement Instructions Lowering in it.

First, let's look at how a call calling convention can be implemented.

SDValue TOYTar-getLoweing::LowerCall(TargetLowering::CallLoweringInfo &CLI, SmallVectorImpl<SDValue> &InVals)
 const {
  SelectionDAG &DAG = CLI.DAG;
  SDLoc &Loc = CLI.DL;
  SmallVectorImpl<ISD::OutputArg> &Outs = CLI.Outs;
  SmallVectorImpl<SDValue> &OutVals = CLI.OutVals;
  SmallVectorImpl<ISD::InputArg> &Ins = CLI.Ins;
  SDValue Chain = CLI.Chain;
  SDValue Callee = CLI.Callee;
  CallingConv::ID CallConv = CLI.CallConv;
  const bool isVarArg = CLI.IsVarArg;

  CLI.IsTailCall = false;

  if (isVarArg) {
    llvm_unreachable("Unimplemented");
  }

  // Analyze operands of the call, assigning locations...