[SLP][NFC]Use DenseSet instead of SetVector, NFC.

For CSEBlocks we can safely use DenseSet, the order should not be
preserved for this container.

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -3034,7 +3034,7 @@ class BoUpSLP {
   SetVector<Instruction *> GatherShuffleExtractSeq;
 
   /// A list of blocks that we are going to CSE.
-  SetVector<BasicBlock *> CSEBlocks;
+  DenseSet<BasicBlock *> CSEBlocks;
 
   /// Contains all scheduling relevant data for an instruction.
   /// A ScheduleData either represents a single instruction or a member of an
@@ -10093,12 +10093,12 @@ class BoUpSLP::ShuffleInstructionBuilder final : public BaseShuffleAnalysis {
     /// Holds all of the instructions that we gathered.
     SetVector<Instruction *> &GatherShuffleExtractSeq;
     /// A list of blocks that we are going to CSE.
-    SetVector<BasicBlock *> &CSEBlocks;
+    DenseSet<BasicBlock *> &CSEBlocks;
 
   public:
     ShuffleIRBuilder(IRBuilderBase &Builder,
                      SetVector<Instruction *> &GatherShuffleExtractSeq,
-                     SetVector<BasicBlock *> &CSEBlocks)
+                     DenseSet<BasicBlock *> &CSEBlocks)
         : Builder(Builder), GatherShuffleExtractSeq(GatherShuffleExtractSeq),
           CSEBlocks(CSEBlocks) {}
     ~ShuffleIRBuilder() = default;