[Mlir-commits] [mlir] [mlir][scf] Add simple LICM pattern for `scf.while` (PR #76370)

[Ivan Butygin]

Hardcode84 wrote:

> or even (for example) interleave CSE and canonicalization until fixed-point?

Yes, and we did it downstream in kind of generic way https://github.com/numba/numba-mlir/blob/main/mlir/lib/Transforms/CompositePass.cpp but there is nothing like this upstream :)

Anyways, I can close this PR an continue with main PR (https://github.com/llvm/llvm-project/pull/76108), making a test pass first, and then making it canonicalization in separate PR.

Also, I'll need to add another pattern which is most likely not qualifies as canonicalization, transforming:
```
%res = scf.while() {
before:
  %1 = foo.bar()
  condition %cond, %1
after(%arg):
  use %arg
}
use %res
```
to
```
scf.while() {
before:
  condition %cond
after():
  %arg = foo.bar()
  use %arg
}
%res = foo.bar()
use %res
```
I initially wanted to add it to uplifting pass itself, but if it will be gone, we probably need another separate pass.

https://github.com/llvm/llvm-project/pull/76370