[llvm] [LV] Use frozen start value for FindLastIV if needed. (PR #132691)

[David Sherwood via llvm-commits]

================
@@ -10448,6 +10451,10 @@ preparePlanForEpilogueVectorLoop(VPlan &Plan, Loop *L,
         ResumeV =
             Builder.CreateICmpNE(ResumeV, RdxDesc.getRecurrenceStartValue());
       } else if (RecurrenceDescriptor::isFindLastIVRecurrenceKind(RK)) {
+        ToFrozen[RdxDesc.getRecurrenceStartValue()] =
+            cast<PHINode>(ResumeV)->getIncomingValueForBlock(
+                EPI.MainLoopIterationCountCheck);
----------------
david-arm wrote:

This confused me at first because there is no obvious indication that `EPI.MainLoopIterationCountCheck` is a Block pointer. Doesn't need doing in this PR, but it would be good to rename `MainLoopIterationCountCheck` to something like `MainLoopIterationCountCheckBlock`.

https://github.com/llvm/llvm-project/pull/132691