[llvm] [VPlan] Manage noalias/alias_scope metadata in VPlan. (NFC) (PR #136450)

[Florian Hahn via llvm-commits]

fhahn wrote:

> Could the no-alias metadata added by loop versioning be managed by a dedicated VPlan-to-VPlan pass, continuing to capture only metadata that propagates from underlying instructions during initial VPlan/recipe construction? May require introducing API to update recipe metadata, but hopefully simple as it merely augments additional nodes?

We could, but we at the moment this would still mean we will be tied to the underlying instruction, which is then used to look up the metadata, which is why added it on construction of the recipes.

We could add VPIRMetadata to VPInstruction, and add the metadata before creating widen recipes (at that point we must have the underlying instruction available, although it might warrant even more a separate class for such VPInstructions at the early stage, raises the question what it should be called and its relationship with VPIRInstruction).

Or change the lookup of the metadata to be based on SCEV, which would require building SCEVs from various VP recipes.  Both may also be good to do as follow-ups

https://github.com/llvm/llvm-project/pull/136450