[VPlan] Retrieve LatchVPBB from region in adjustRecipesForRed (NFC)

The HeaderVPBB is retrieved in a similar fashion already.

This is in preparation for splitting up the very large
tryToBuildVPlanWithVPRecipes into several distinct functions, as
suggested multiple times, including in
#94760

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h

@@ -428,7 +428,7 @@ class LoopVectorizationPlanner {
   // converted to reductions, with one operand being vector and the other being
   // the scalar reduction chain. For other reductions, a select is introduced
   // between the phi and live-out recipes when folding the tail.
-  void adjustRecipesForReductions(VPBasicBlock *LatchVPBB, VPlanPtr &Plan,
+  void adjustRecipesForReductions(VPlanPtr &Plan,
                                   VPRecipeBuilder &RecipeBuilder,
                                   ElementCount MinVF);
 

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -8696,7 +8696,7 @@ LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(VFRange &Range) {
   // ---------------------------------------------------------------------------
 
   // Adjust the recipes for any inloop reductions.
-  adjustRecipesForReductions(LatchVPBB, Plan, RecipeBuilder, Range.Start);
+  adjustRecipesForReductions(Plan, RecipeBuilder, Range.Start);
 
   // Interleave memory: for each Interleave Group we marked earlier as relevant
   // for this VPlan, replace the Recipes widening its memory instructions with a
@@ -8838,8 +8838,7 @@ VPlanPtr LoopVectorizationPlanner::buildVPlan(VFRange &Range) {
 // with a boolean reduction phi node to check if the condition is true in any
 // iteration. The final value is selected by the final ComputeReductionResult.
 void LoopVectorizationPlanner::adjustRecipesForReductions(
-    VPBasicBlock *LatchVPBB, VPlanPtr &Plan, VPRecipeBuilder &RecipeBuilder,
-    ElementCount MinVF) {
+    VPlanPtr &Plan, VPRecipeBuilder &RecipeBuilder, ElementCount MinVF) {
   VPRegionBlock *VectorLoopRegion = Plan->getVectorLoopRegion();
   VPBasicBlock *Header = VectorLoopRegion->getEntryBasicBlock();
   // Gather all VPReductionPHIRecipe and sort them so that Intermediate stores
@@ -9003,6 +9002,7 @@ void LoopVectorizationPlanner::adjustRecipesForReductions(
       PreviousLink = RedRecipe;
     }
   }
+  VPBasicBlock *LatchVPBB = VectorLoopRegion->getExitingBasicBlock();
   Builder.setInsertPoint(&*LatchVPBB->begin());
   VPBasicBlock *MiddleVPBB =
       cast<VPBasicBlock>(VectorLoopRegion->getSingleSuccessor());