Reapply "[VPlan] Detect and create partial reductions in VPlan. (NFCI) (#167851)"
This reverts commit d1e477b00b49c63ff4dd513eeb14a5b18bc055d7.
Recommit with a extra checks making sure extends are VPWidenCastRecipes,
rejecting VPReplicateRecipes.
Original message:
As a first step, move the existing partial reduction detection logic to
VPlan, trying to preserve the existing code structure & behavior as
closely as possible.
With this, partial reductions are detected and created together in a
single step.
This allows forming partial reductions and bundling them up if
profitable together in a follow-up.
PR: https://github.com/llvm/llvm-project/pull/167851
llvm-project
90b3712d - Reapply "[VPlan] Detect and create partial reductions in VPlan. (NFCI) (#167851)"
