This is a generalization of the LookupPtrRegClass mechanism.
AMDGPU has several use cases for swapping the register class of
instruction operands based on the subtarget, but none of them
really fit into the box of being pointer-like.
The current system requires manual management of an arbitrary integer
ID. For the AMDGPU use case, this would end up being around 40 new
entries to manage.
This just introduces the base infrastructure. I have ports of all
the target specific usage of PointerLikeRegClass ready.
This is needed to provide proper size and offset for the GPRPair subreg
indices on RISC-V. The size of a GPR already uses HwMode. Previously we
said the subreg indices have unknown size and offset, but this stops
DwarfExpression::addMachineReg from being able to find the registers
that make up the pair.
I believe this fixes https://github.com/llvm/llvm-project/issues/85864
but need to verify.
Refactor of the llvm-tblgen source into:
- a "Basic" library, which contains the bare minimum utilities to build
`llvm-min-tablegen`
- a "Common" library which contains all of the helpers for TableGen
backends. Such helpers can be shared by more than one backend, and even
unit tested (e.g. CodeExpander is, maybe we can add more over time)
Fixes#80647
