For selecting a machine-specific instruction, a separate class, TOYDAGToDAGISel, needs to be defined. To compile the file containing this class definition, add the filename to the CMakeLists.txt file in the TOY folder:

$ vi CMakeLists .txt
add_llvm_target(...
...
TOYISelDAGToDAG.cpp
...
)

A pass entry needs to be added in the TOYTargetMachine.h and TOYTargetMachine.cpp files:

$ vi TOYTargetMachine.h
const TOYInstrInfo *getInstrInfo() const override {
return getSubtargetImpl()->getInstrInfo();
}

The following code in TOYTargetMachine.cpp will create a pass in the instruction selection stage:

class TOYPassConfig : public TargetPassConfig {
public:
...
virtual bool addInstSelector();
};
...
bool TOYPassConfig::addInstSelector() {
addPass...