[llvm-branch-commits] [llvm] [LoopVectorize] Support vectorization of compressing patterns in VPlan (PR #140723)

[Andrei Elovikov via llvm-branch-commits]

eas wrote:

Tiny bit of feedback if there is still interest in it. I think this would benefit from a VPlan-dump-based test under `test/LoopVectorize/VPlan`, probably extending the printing of the recipe to include information if the store is compressed or not.

For negative tests, it would help to add a comment to explain if it's fundamentally wrong to vectorize or just a TODO for a future improvement (and maybe some of the positive could benefit from extra comments as well). I also didn't see a negative test with an "invalid" extra use of a phi in the middle of the phi-chain (maybe I just missed).

Another potentially interesting test would be

```
  if (condition) {
    a[idx] = ...;
    b[idx] = ...;  // multiple use
    idx += 1;
  }
```

Github shows "no conflicts with base branch" but that's probably because of the stacked PRs.


https://github.com/llvm/llvm-project/pull/140723