MIPS ISel Passes

// llvm/lib/Target/Mips/MipsTargetMachine.cpp
// parent->child: TargetPassConfig -> MipsPassConfig

// Install an instruction selector pass using
// the ISelDag to gen Mips code.
bool MipsPassConfig::addInstSelector() {
  addPass(createMipsModuleISelDagPass());
  addPass(createMips16ISelDag(getMipsTargetMachine(), getOptLevel()));
  addPass(createMipsSEISelDag(getMipsTargetMachine(), getOptLevel()));
  return false;
}

// createMipsModuleISelDagPass()
// llvm/lib/Target/Mips/MipsModuleISelDAGToDAG.cpp
llvm::FunctionPass *llvm::createMipsModuleISelDagPass() {
  return new MipsModuleDAGToDAGISel();
}

// createMips16ISelDag()
// llvm/lib/Target/Mips/Mips16ISelDAGToDAG.cpp
FunctionPass *llvm::createMips16ISelDag(MipsTargetMachine &TM,
                                        CodeGenOpt::Level OptLevel) {
  return new Mips16DAGToDAGISel(TM, OptLevel);
}

// createMipsSEISelDag()
FunctionPass *llvm::createMipsSEISelDag(MipsTargetMachine &TM,
                                        CodeGenOpt::Level OptLevel) {
  return new MipsSEDAGToDAGISel(TM, OptLevel);
}

MachineFunctionPass
 -> SelectionDAGISel
  -> MipsDAGToDAGISel
   -> MipsSEDAGToDAGISel

// llvm/lib/Target/Mips/MipsSEISelDAGToDAG.cpp

bool MipsSEDAGToDAGISel::runOnMachineFunction(MachineFunction &MF) {
  Subtarget = &static_cast<const MipsSubtarget &>(MF.getSubtarget());
  if (Subtarget->inMips16Mode())
    return false;
  return MipsDAGToDAGISel::runOnMachineFunction(MF);
}

// MipsDAGToDAGISel::runOnMachineFunction
// llvm/lib/Target/Mips/MipsISelDAGToDAG.cpp

bool MipsDAGToDAGISel::runOnMachineFunction(MachineFunction &MF) {
  Subtarget = &static_cast<const MipsSubtarget &>(MF.getSubtarget());

  DebugLL("MipsDAGToDAGISel pass on MF: "<< MF.getName() << "\n")

  bool Ret = SelectionDAGISel::runOnMachineFunction(MF);

  processFunctionAfterISel(MF);

  return Ret;
}

// llvm/lib/Target/Mips/MipsModuleISelDAGToDAG.cpp

bool MipsModuleDAGToDAGISel::runOnMachineFunction(MachineFunction &MF) {
  LLVM_DEBUG(errs() << "In MipsModuleDAGToDAGISel::runMachineFunction\n");
  auto &TPC = getAnalysis<TargetPassConfig>();
  auto &TM = TPC.getTM<MipsTargetMachine>();
  TM.resetSubtarget(&MF);
  return false;
}

// MipsTargetMachine::resetSubTarget()
// llvm/lib/Target/Mips/MipsTargetMachine.cpp
void MipsTargetMachine::resetSubtarget(MachineFunction *MF) {
  LLVM_DEBUG(dbgs() << "resetSubtarget\n");

  Subtarget = &MF->getSubtarget<MipsSubtarget>();
}

MachineFunctionPass
 -> SelectionDAGISel
  -> MipsDAGToDAGISel 
    -> Mips16DAGToDAGISel

// llvm/lib/Target/Mips/Mips16ISelDAGToDAG.cpp

bool Mips16DAGToDAGISel::runOnMachineFunction(MachineFunction &MF) {
  Subtarget = &static_cast<const MipsSubtarget &>(MF.getSubtarget());

  DebugLL("Mips16DAGToDAGISel pass on MF: "<< MF.getName() << "\n");

  if (!Subtarget->inMips16Mode())
    return false;
  return MipsDAGToDAGISel::runOnMachineFunction(MF);
}