[SLP][NFC]Remove extra unused vars, add TODO, NFC.

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -6961,13 +6961,12 @@ class BoUpSLP::ShuffleCostEstimator : public BaseShuffleAnalysis {
                  }))) &&
         !all_of(Gathers, [&](Value *V) { return R.getTreeEntry(V); }) &&
         !isSplat(Gathers)) {
-      BoUpSLP::ValueSet VectorizedLoads;
+      SetVector<Value *> VectorizedLoads;
       SmallVector<LoadInst *> VectorizedStarts;
       SmallVector<std::pair<unsigned, unsigned>> ScatterVectorized;
       unsigned StartIdx = 0;
       unsigned VF = VL.size() / 2;
-      const unsigned Sz = R.DL->getTypeSizeInBits(VL.front()->getType());
-      for (unsigned MinVF = R.getMinVF(2 * Sz); VF >= MinVF; VF /= 2) {
+      for (; VF >= MinVF; VF /= 2) {
         for (unsigned Cnt = StartIdx, End = VL.size(); Cnt + VF <= End;
              Cnt += VF) {
           ArrayRef<Value *> Slice = VL.slice(Cnt, VF);
@@ -6990,6 +6989,7 @@ class BoUpSLP::ShuffleCostEstimator : public BaseShuffleAnalysis {
             case LoadsState::PossibleStridedVectorize:
               // Mark the vectorized loads so that we don't vectorize them
               // again.
+              // TODO: better handling of loads with reorders.
               if (LS == LoadsState::Vectorize && CurrentOrder.empty())
                 VectorizedStarts.push_back(cast<LoadInst>(Slice.front()));
               else