[VPlan] Remove unused VPTransformState::VPValue2Value (NFCI).

Clean up unused member variable.

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -829,10 +829,6 @@ void VPlan::prepareToExecute(Value *TripCountV, Value *VectorTripCountV,
 /// Assumes a single pre-header basic-block was created for this. Introduce
 /// additional basic-blocks as needed, and fill them all.
 void VPlan::execute(VPTransformState *State) {
-  // Set the reverse mapping from VPValues to Values for code generation.
-  for (auto &Entry : Value2VPValue)
-    State->VPValue2Value[Entry.second] = Entry.first;
-
   // Initialize CFG state.
   State->CFG.PrevVPBB = nullptr;
   State->CFG.ExitBB = State->CFG.PrevBB->getSingleSuccessor();

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -383,8 +383,6 @@ struct VPTransformState {
   /// Hold a reference to the IRBuilder used to generate output IR code.
   IRBuilderBase &Builder;
 
-  VPValue2ValueTy VPValue2Value;
-
   /// Hold a pointer to InnerLoopVectorizer to reuse its IR generation methods.
   InnerLoopVectorizer *ILV;