Lowering the ABI with SDISel
To lower the ABI with SDISel, you must implement the four methods of your target-specific version of the TargetLowering class that are responsible for this part of the selector. Specifically, you must implement the LowerFormalArguments, LowerReturn, LowerCall, and CanLowerReturn methods. These methods map exactly to the logic we said you would need to provide at the beginning of the Overview of the IR building section.
Concretely, as we hinted previously, the implementation of these methods will rely heavily on the CCState and the CCValAssign classes. More specifically, you need to use one of the CCState::AnalyzeXXX methods with a proper CCAssignFn instance (the one you produced with TableGen) to produce a list of CCValAssign instances. The CCState::AnalyzeXXX method to use depends on what you are trying to achieve:
AnalyzeFormalArguments: Use this method when producing the sequence of instructions to read the arguments from within acallee...
