[SLP] Remove unnecessary member variables by using container APIs.

[mcrosier]

Summary

Please have a look.

Chad

[mcrosier]

Update the debug output accordingly. This is a functional change.

[mssimpso]

LGTM.

lib/Transforms/Vectorize/SLPVectorizer.cpp

bool runOnFunction(Function &F) override {
     // A general note: the vectorizer must use BoUpSLP::eraseInstruction() to
     // delete instructions.
 
     // Scan the blocks in the function in post order.
     for (auto BB : post_order(&F.getEntryBlock())) {
       collectSeedInstructions(BB);
 
       // Vectorize trees that end at stores.
-      if (NumStores > 0) {
-        DEBUG(dbgs() << "SLP: Found " << NumStores << " stores.\n");
+      if (!Stores.empty()) {
+        DEBUG(dbgs() << "SLP: Found " << Stores.size() << " stores.\n");
         Changed |= vectorizeStoreChains(R);
       }
 
       // Vectorize trees that end at reductions.
       Changed |= vectorizeChainsInBlock(BB, R);
 
       // Vectorize the index computations of getelementptr instructions. This
       // is primarily intended to catch gather-like idioms ending at
       // non-consecutive loads.
-      if (NumGEPs > 0) {
-        DEBUG(dbgs() << "SLP: Found " << NumGEPs << " GEPs.\n");
+      if (!GEPs.empty()) {
+        DEBUG(dbgs() << "SLP: Found " << GEPs.size() << " GEPs.\n");
         Changed |= vectorizeGEPIndices(BB, R);
       }
     }
 
     if (Changed) {
       R.optimizeGatherSequence();
       DEBUG(dbgs() << "SLP: vectorized \"" << F.getName() << "\"\n");
       DEBUG(verifyFunction(F));
bool vectorizeStores(ArrayRef<StoreInst *> Stores, int costThreshold,
                        BoUpSLP &R);
 
   /// The store instructions in a basic block organized by base pointer.
   StoreListMap Stores;
 
   /// The getelementptr instructions in a basic block organized by base pointer.
   WeakVHListMap GEPs;
 
-  /// The number of store instructions in a basic block.
-  unsigned NumStores;
-
-  /// The number of getelementptr instructions in a basic block.
-  unsigned NumGEPs;
-
   unsigned MaxVecRegSize; // This is set by TTI or overridden by cl::opt.
   unsigned MinVecRegSize; // Set by cl::opt (default: 128).
 };
 
 /// \brief Check that the Values in the slice in VL array are still existent in
 /// the WeakVH array.
 /// Vectorization of part of the VL array may cause later values in the VL array
 /// to become invalid. We track when this has happened in the WeakVH array.
bool SLPVectorizer::vectorizeStores(ArrayRef<StoreInst *> Stores,
   return Changed;
 }
 
 void SLPVectorizer::collectSeedInstructions(BasicBlock *BB) {
 
   // Initialize the collections. We will make a single pass over the block.
   Stores.clear();
   GEPs.clear();
-  NumStores = NumGEPs = 0;
 
   // Visit the store and getelementptr instructions in BB and organize them in
   // Stores and GEPs according to the underlying objects of their pointer
   // operands.
   for (Instruction &I : *BB) {
 
     // Ignore store instructions that are volatile or have a pointer operand
     // that doesn't point to a scalar type.
     if (auto *SI = dyn_cast<StoreInst>(&I)) {
       if (!SI->isSimple())
         continue;
       if (!isValidElementType(SI->getValueOperand()->getType()))
         continue;
       Stores[GetUnderlyingObject(SI->getPointerOperand(), *DL)].push_back(SI);
-      ++NumStores;
     }
 
     // Ignore getelementptr instructions that have more than one index, a
     // constant index, or a pointer operand that doesn't point to a scalar
     // type.
     else if (auto *GEP = dyn_cast<GetElementPtrInst>(&I)) {
       auto Idx = GEP->idx_begin()->get();
       if (GEP->getNumIndices() > 1 || isa<Constant>(Idx))
         continue;
       if (!isValidElementType(Idx->getType()))
         continue;
       GEPs[GetUnderlyingObject(GEP->getPointerOperand(), *DL)].push_back(GEP);
-      ++NumGEPs;
     }
   }
 }
 
 bool SLPVectorizer::tryToVectorizePair(Value *A, Value *B, BoUpSLP &R) {
   if (!A || !B)
     return false;
   Value *VL[] = { A, B };