[VPlan] Remove fixHeaderPhis (NFC).

Removes unneeded code after #124432.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -8675,16 +8675,6 @@ VPRecipeBuilder::tryToWidenHistogram(const HistogramInfo *HI,
                                HI->Store->getDebugLoc());
 }
 
-void VPRecipeBuilder::fixHeaderPhis() {
-  BasicBlock *OrigLatch = OrigLoop->getLoopLatch();
-  for (VPHeaderPHIRecipe *R : PhisToFix) {
-    auto *PN = cast<PHINode>(R->getUnderlyingValue());
-    VPRecipeBase *IncR =
-        getRecipe(cast<Instruction>(PN->getIncomingValueForBlock(OrigLatch)));
-    R->addOperand(IncR->getVPSingleValue());
-  }
-}
-
 VPReplicateRecipe *
 VPRecipeBuilder::handleReplication(Instruction *I, ArrayRef<VPValue *> Operands,
                                    VFRange &Range) {
@@ -8870,6 +8860,7 @@ VPRecipeBase *VPRecipeBuilder::tryToCreateWidenRecipe(
     if (Phi->getParent() != OrigLoop->getHeader())
       return tryToBlend(Phi, Operands);
 
+    assert(Operands.size() == 2 && "Must have 2 operands for header phis");
     if ((Recipe = tryToOptimizeInductionPHI(Phi, Operands, Range)))
       return Recipe;
 
@@ -8897,8 +8888,8 @@ VPRecipeBase *VPRecipeBuilder::tryToCreateWidenRecipe(
       // directly, enabling more efficient codegen.
       PhiRecipe = new VPFirstOrderRecurrencePHIRecipe(Phi, *StartV);
     }
-
-    PhisToFix.push_back(PhiRecipe);
+    // Add backedge value.
+    PhiRecipe->addOperand(Operands[1]);
     return PhiRecipe;
   }
 
@@ -9500,7 +9491,6 @@ LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(VFRange &Range) {
          !Plan->getVectorLoopRegion()->getEntryBasicBlock()->empty() &&
          "entry block must be set to a VPRegionBlock having a non-empty entry "
          "VPBasicBlock");
-  RecipeBuilder.fixHeaderPhis();
 
   // Update wide induction increments to use the same step as the corresponding
   // wide induction. This enables detecting induction increments directly in

llvm/lib/Transforms/Vectorize/VPRecipeBuilder.h

@@ -225,10 +225,6 @@ class VPRecipeBuilder {
                                        ArrayRef<VPValue *> Operands,
                                        VFRange &Range);
 
-  /// Add the incoming values from the backedge to reduction & first-order
-  /// recurrence cross-iteration phis.
-  void fixHeaderPhis();
-
   VPValue *getVPValueOrAddLiveIn(Value *V) {
     if (auto *I = dyn_cast<Instruction>(V)) {
       if (auto *R = Ingredient2Recipe.lookup(I))