[llvm] [VPlan] Introduce ComputeReductionResult VPInstruction opcode. (PR #70253)

[via llvm-commits]

================
@@ -7664,6 +7531,17 @@ SCEV2ValueTy LoopVectorizationPlanner::executePlan(
 
   BestVPlan.execute(&State);
 
+  // 2.5 Collect reduction resume values.
+  DenseMap<const RecurrenceDescriptor *, Value *> ReductionResumeValues;
----------------
ayalz wrote:

Note that updating ReductionResumeValues is needed only when !IsEpilogueVectorization, but collectMergePhiForReduction() is called unconditionally because it introduces phi's into the scalar preheader, for both main and epilog loops.

https://github.com/llvm/llvm-project/pull/70253