[all-commits] [llvm/llvm-project] 08165c: [RISCV] Add searchable table for tune information ...

[Wang Pengcheng via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 08165c444e11defd42d417fa88a3dede83b230e5
      https://github.com/llvm/llvm-project/commit/08165c444e11defd42d417fa88a3dede83b230e5
  Author: Wang Pengcheng <137158460+wangpc-pp at users.noreply.github.com>
  Date:   2023-09-26 (Tue, 26 Sep 2023)

  Changed paths:
    M llvm/lib/Target/RISCV/RISCVFeatures.td
    M llvm/lib/Target/RISCV/RISCVProcessors.td
    M llvm/lib/Target/RISCV/RISCVSubtarget.cpp
    M llvm/lib/Target/RISCV/RISCVSubtarget.h
    M llvm/test/CodeGen/RISCV/align-loops.ll
    M llvm/test/CodeGen/RISCV/align.ll

  Log Message:
  -----------
  [RISCV] Add searchable table for tune information (#66193)

There are many information that can be used for tuning, like
alignments, cache line size, etc. But we can't make all of them
`SubtargetFeature` because some of them are not with enumerable
value, for example, `PrefetchDistance` used by `LoopDataPrefetch`.

In this patch, a searchable table `RISCVTuneInfoTable` is added,
in which each entry contains the CPU name and all tune information
defined in `RISCVTuneInfo`. Each field of `RISCVTuneInfo` should
have a default value and processor definitions can override the
default value via `let` statements.

We don't need to define a `RISCVTuneInfo` for each processor and
it will use the default value (which is for `generic`) if no
`RISCVTuneInfo` defined.

For processors in the same series, a subclass can inherit from
`RISCVTuneInfo` and override the fields. And we can also override
the fields in processor definitions if there are some differences
in the same processor series.

When initilizing `RISCVSubtarget`, we will use `TuneCPU` as the
key to serach the tune info table. So, the behavior here is if
we don't specify the tune CPU, we will use specified `CPU`, which
is expected I think. 

This patch almost undoes 61ab106, in which I added tune features
of preferred function/loop alignments. More tune information can
be added in the future.