[llvm] [VPlan] Introduce VPScalarPHIRecipe, use for can & EVL IV codegen (NFC). (PR #114305)

[via llvm-commits]

================
@@ -3165,6 +3152,12 @@ void VPWidenPointerInductionRecipe::execute(VPTransformState &State) {
   BasicBlock *VectorPH = State.CFG.getPreheaderBBFor(this);
   PHINode *NewPointerPhi = nullptr;
   if (CurrentPart == 0) {
+    auto *IVR = cast<VPHeaderPHIRecipe>(&getParent()
+                                             ->getPlan()
+                                             ->getVectorLoopRegion()
+                                             ->getEntryBasicBlock()
+                                             ->front());
----------------
ayalz wrote:

This deserves a method, being getCanonicalIV() w/o casting its result to VPCanonicalIVPHIRecipe?

https://github.com/llvm/llvm-project/pull/114305