[llvm-branch-commits] [llvm] [VPlan] Initial modeling of runtime VF * UF as VPValue. (PR #74761)

[Florian Hahn via llvm-branch-commits]

https://github.com/fhahn created https://github.com/llvm/llvm-project/pull/74761

This patch starts initial modeling of runtime VF * UF in VPlan.
Initially, introduce a dedicated RuntimeVFxUF VPValue, which is then
populated during VPlan::prepareToExecute. Initially, the runtime
VF * UF applies only to the main vector loop region. Once we extend the
scope of VPlan in the future, we may want to associate different VFxUFs
with different vector loop regions (e.g. the epilogue vector loop)

This allows explicitly parameterizing recipes that rely on the runtime
VF * UF, like the canonical induction increment. At the moment, this
mainly helps to avoid generating some duplicated calls to vscale with
scalable vectors. It should also allow using EVL as induction increments
explicitly in D99750. Referring to VF * UF is also needed in other
places that we plan to migrate to VPlan, like the minimum trip count
check during skeleton creation.

The first version creates the value for VF * UF directly in
prepareToExecute to limit the scope of the patch. A follow-on patch will
model VF * UF computation explicitly in VPlan using recipes.

Moved from Phabricator (https://reviews.llvm.org/D157322)