Summary:
This patch handles the types(MVT) in `selectionDAG` for RISCV vector
tuples.
As described in previous patch handling llvm types, the MVTs also have
32 variants:
```
riscv_nxv1i8x2, riscv_nxv1i8x3, riscv_nxv1i8x4, riscv_nxv1i8x5, riscv_nxv1i8x6, riscv_nxv1i8x7, riscv_nxv1i8x8,
riscv_nxv2i8x2, riscv_nxv2i8x3, riscv_nxv2i8x4, riscv_nxv2i8x5, riscv_nxv2i8x6, riscv_nxv2i8x7, riscv_nxv2i8x8,
riscv_nxv4i8x2, riscv_nxv4i8x3, riscv_nxv4i8x4, riscv_nxv4i8x5, riscv_nxv4i8x6, riscv_nxv4i8x7, riscv_nxv4i8x8,
riscv_nxv8i8x2, riscv_nxv8i8x3, riscv_nxv8i8x4, riscv_nxv8i8x5, riscv_nxv8i8x6, riscv_nxv8i8x7, riscv_nxv8i8x8,
riscv_nxv16i8x2, riscv_nxv16i8x3, riscv_nxv16i8x4,
riscv_nxv32i8x2.
```
Detail:
An intuitive way to model vector tuple type is using nested scalable
vector, e.g. `nElts=NF, EltTy=nxv2i32`. However it's not compatible to
what we've done to handle scalable vector in TargetLowering, so it would
need more effort to change the code to handle this concept.
Another approach is encoding the `MinNumElts` info in `sz` of `MVT`,
e.g.
`nElts=NF, sz=(NF*MinNumElts*8)`, this makes it much easier to handle
and
changes less code.
This patch adopts the latter approach.
Stacked on https://github.com/llvm/llvm-project/pull/97992
Implement MVT::getVectorElementType and MVT::getVectorMinNumElements
with table lookup instead of switch.
This speeds up "check-llvm-codegen-amdgpu" by about 7% in my Release
build.
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
