[VPlan] Scalarize to first-lane-only directly on VPlan (#184267)
This is needed to enable subsequent
https://github.com/llvm/llvm-project/pull/182595.
I don't think we can fully port all scalarization logic from the legacy
path to VPlan-based right now because by that point in the pipeline
interleave groups aren't lowered into any VPlan-based representation and
as such this pass operates on incomplete information. Currently, the
pass can make transformations if "all uses are scalar" (that won't
change later) but not "are uses a mix of vector and scalar uses" (that
might change after lowering interleave groups).
As such, I decided just to implement something much simpler that would
be enough for #182595. However, we perform this transformation before
delegating to the old CM-based decision, so it **is** effective
immediately and taking precedence even for consecutive loads/stores
right away.
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Co-authored-by: Ramkumar Ramachandra <artagnon@tenstorrent.com>
llvm-project
0e0c9a5c - [VPlan] Scalarize to first-lane-only directly on VPlan (#184267)
