Porting GlobalISel to A New Target

There are four major classes to implement by the target:

• CallLowering — lower calls, returns, and arguments according to the ABI.

• RegisterBankInfo — describe Register Bank coverage, cross-bank copy cost, and the mapping of operands onto banks for each instruction.

• LegalizerInfo — describe what is legal, and how to legalize what isn’t.

• InstructionSelector — select generic MIR to target-specific MIR.

Additionally:

• TargetPassConfig — create the passes constituting the pipeline, including additional passes not included in the Core Pipeline.

Tutorials

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.