There are four major classes to implement by the target:
- :ref:`CallLowering <translator-call-lower>` --- lower calls, returns, and arguments according to the ABI.
- :ref:`RegisterBankInfo <api-registerbankinfo>` --- describe :ref:`gmir-regbank` coverage, cross-bank copy cost, and the mapping of operands onto banks for each instruction.
- :ref:`LegalizerInfo <api-legalizerinfo>` --- describe what is legal, and how to legalize what isn't.
- :ref:`InstructionSelector <api-instructionselector>` --- select generic MIR to target-specific MIR.
Additionally:
TargetPassConfig--- create the passes constituting the pipeline, including additional passes not included in the :ref:`pipeline`.
We'd recommend watching this tutorial from the 2017 LLVM DevMeeting which gave an overview of how to bring up a new backend in GlobalISel.