[SLP][NFC] Cleanup: Remove KeyNodes set.

[vporpo]

Summary

I don't see a good reason form having the KeyNodes set.
This patch removes the set.

[ABataev]

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

14679–14680

You can remove this container too, since it is not used anymore.

[vporpo]

Remove KeyNodes.

[ABataev]

LG

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

HaveVectorizedPhiNodes = tryToVectorizeSequence<Value>(
         /*MaxVFOnly=*/true, R);
     Changed |= HaveVectorizedPhiNodes;
     VisitedInstrs.insert(Incoming.begin(), Incoming.end());
   } while (HaveVectorizedPhiNodes);
 
   VisitedInstrs.clear();
 
   InstSetVector PostProcessInserts;
   SmallSetVector<CmpInst *, 8> PostProcessCmps;
-  SmallDenseSet<Instruction *, 4> KeyNodes;
   // Vectorizes Inserts in `PostProcessInserts` and if `VecctorizeCmps` is true
   // also vectorizes `PostProcessCmps`.
   auto VectorizeInsertsAndCmps = [&](bool VectorizeCmps) {
     bool Changed = vectorizeInserts(PostProcessInserts, BB, R);
     if (VectorizeCmps) {
       Changed |= vectorizeCmpInsts(reverse(PostProcessCmps), BB, R);
       PostProcessCmps.clear();
     }
     PostProcessInserts.clear();
     return Changed;
   };
   // Returns true if `I` is in `PostProcessInserts` or `PostProcessCmps`.
   auto IsInPostProcessInstrs = [&](Instruction *I) {
     if (auto *Cmp = dyn_cast<CmpInst>(I))
       return PostProcessCmps.contains(Cmp);
     return isa<InsertElementInst, InsertValueInst>(I) &&
            PostProcessInserts.contains(I);
   };
+  // Returns true if `I` is an instruction without users, like terminator, or
+  // function call with ignored return value, store. Ignore unused instructions
+  // (basing on instruction type, except for CallInst and InvokeInst).
+  auto HasNoUsers = [](Instruction *I) {
+    return I->use_empty() &&
+           (I->getType()->isVoidTy() || isa<CallInst, InvokeInst>(I));
+  };
   for (BasicBlock::iterator it = BB->begin(), e = BB->end(); it != e; ++it) {
     // Skip instructions with scalable type. The num of elements is unknown at
     // compile-time for scalable type.
     if (isa<ScalableVectorType>(it->getType()))
       continue;
 
     // Skip instructions marked for the deletion.
     if (R.isDeleted(&*it))
       continue;
     // We may go through BB multiple times so skip the one we have checked.
     if (!VisitedInstrs.insert(&*it).second) {
-      if (it->use_empty() && KeyNodes.contains(&*it) &&
+      if (HasNoUsers(&*it) &&
           VectorizeInsertsAndCmps(/*VectorizeCmps=*/it->isTerminator())) {
         // We would like to start over since some instructions are deleted
         // and the iterator may become invalid value.
         Changed = true;
         it = BB->begin();
         e = BB->end();
       }
       continue;
if (PHINode *P = dyn_cast<PHINode>(it)) {
         if (auto *PI = dyn_cast<Instruction>(P->getIncomingValue(I));
             PI && !IsInPostProcessInstrs(PI))
           Changed |= vectorizeRootInstruction(nullptr, PI,
                                               P->getIncomingBlock(I), R, TTI);
       }
       continue;
     }
 
-    // Ran into an instruction without users, like terminator, or function call
-    // with ignored return value, store. Ignore unused instructions (basing on
-    // instruction type, except for CallInst and InvokeInst).
-    if (it->use_empty() &&
-        (it->getType()->isVoidTy() || isa<CallInst, InvokeInst>(it))) {
-      KeyNodes.insert(&*it);
+    if (HasNoUsers(&*it)) {
       bool OpsChanged = false;
       auto *SI = dyn_cast<StoreInst>(it);
       bool TryToVectorizeRoot = ShouldStartVectorizeHorAtStore || !SI;
       if (SI) {
         auto I = Stores.find(getUnderlyingObject(SI->getPointerOperand()));
         // Try to vectorize chain in store, if this is the only store to the
         // address in the block.
         // TODO: This is just a temporarily solution to save compile time. Need