[llvm] [SLP]Reduce number of alternate instruction, where possible (PR #128907)

[via llvm-commits]

hiraditya wrote:

> > needs rebase and clang format.
> 
> No, it does not. The check failed because of undefs, which are generated by builder constant folder and not related to the patch

i see. there is one tset failure showing up in the last build https://buildkite.com/llvm-project/github-pull-requests/builds/154547#0195706c-d4c0-4a5b-bd8b-1fddfc3bc646

```
Failed Tests (1):
  LLVM :: Transforms/InstCombine/AMDGPU/simplify-demanded-vector-elts-lane-intrinsics.ll
```


https://github.com/llvm/llvm-project/pull/128907