[VPlan] Introduce and use VPValue::replaceUsesOfWith (NFC).

Adds an API matching LLVM's IR Value, which simplifies some code a
bit.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -9924,11 +9924,8 @@ void LoopVectorizationPlanner::adjustRecipesForReductions(
       VPValue *Cmp = Select->getOperand(0);
       // If the compare is checking the reduction PHI node, adjust it to check
       // the start value.
-      if (VPRecipeBase *CmpR = Cmp->getDefiningRecipe()) {
-        for (unsigned I = 0; I != CmpR->getNumOperands(); ++I)
-          if (CmpR->getOperand(I) == PhiR)
-            CmpR->setOperand(I, PhiR->getStartValue());
-      }
+      if (VPRecipeBase *CmpR = Cmp->getDefiningRecipe())
+        CmpR->replaceUsesOfWith(PhiR, PhiR->getStartValue());
       Builder.setInsertPoint(Select);
 
       // If the true value of the select is the reduction phi, the new value is

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -1414,6 +1414,13 @@ void VPValue::replaceUsesWithIf(
   }
 }
 
+void VPUser::replaceUsesOfWith(VPValue *From, VPValue *To) {
+  for (unsigned Idx = 0; Idx != getNumOperands(); ++Idx) {
+    if (getOperand(Idx) == From)
+      setOperand(Idx, To);
+  }
+}
+
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 void VPValue::printAsOperand(raw_ostream &OS, VPSlotTracker &Tracker) const {
   OS << Tracker.getOrCreateName(this);

llvm/lib/Transforms/Vectorize/VPlanValue.h

@@ -246,6 +246,9 @@ class VPUser {
     New->addUser(*this);
   }
 
+  /// Replaces all uses of \p From in the VPUser with \p To.
+  void replaceUsesOfWith(VPValue *From, VPValue *To);
+
   typedef SmallVectorImpl<VPValue *>::iterator operand_iterator;
   typedef SmallVectorImpl<VPValue *>::const_iterator const_operand_iterator;
   typedef iterator_range<operand_iterator> operand_range;