Revert "[SLP]Fix non-determinism in reused elements analysis"

This reverts commit 3158525 to fix
a bug revealed in https://lab.llvm.org/buildbot/#/builders/123/builds/14930

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -3801,7 +3801,7 @@ class BoUpSLP {
   SetVector<const TreeEntry *> PostponedGathers;
 
   using ValueToGatherNodesMap =
-      DenseMap<Value *, SmallSetVector<const TreeEntry *, 4>>;
+      DenseMap<Value *, SmallPtrSet<const TreeEntry *, 4>>;
   ValueToGatherNodesMap ValueToGatherNodes;
 
   /// A list of the load entries (node indices), which can be vectorized using
@@ -8328,15 +8328,14 @@ class PHIHandler {
       }
       return;
     }
-    SmallMapVector<std::pair<BasicBlock *, unsigned>, SmallVector<unsigned>, 4>
-        Blocks;
-    for (unsigned I : seq<unsigned>(Main->getNumIncomingValues())) {
+    SmallDenseMap<BasicBlock *, SmallVector<unsigned>, 4> Blocks;
+    for (unsigned I : seq<unsigned>(0, Main->getNumIncomingValues())) {
       BasicBlock *InBB = Main->getIncomingBlock(I);
       if (!DT.isReachableFromEntry(InBB)) {
         Operands[I].assign(Phis.size(), PoisonValue::get(Main->getType()));
         continue;
       }
-      Blocks.try_emplace(std::make_pair(InBB, I)).first->second.push_back(I);
+      Blocks.try_emplace(InBB).first->second.push_back(I);
     }
     for (auto [Idx, V] : enumerate(Phis)) {
       if (isa<PoisonValue>(V)) {
@@ -8345,26 +8344,25 @@ class PHIHandler {
         continue;
       }
       auto *P = cast<PHINode>(V);
-      for (unsigned I : seq<unsigned>(P->getNumIncomingValues())) {
+      for (unsigned I : seq<unsigned>(0, P->getNumIncomingValues())) {
         BasicBlock *InBB = P->getIncomingBlock(I);
         if (InBB == Main->getIncomingBlock(I)) {
           if (isa_and_nonnull<PoisonValue>(Operands[I][Idx]))
             continue;
           Operands[I][Idx] = P->getIncomingValue(I);
           continue;
         }
-        auto *It = Blocks.find(std::make_pair(InBB, I));
+        auto It = Blocks.find(InBB);
         if (It == Blocks.end())
           continue;
         Operands[It->second.front()][Idx] = P->getIncomingValue(I);
       }
     }
     for (const auto &P : Blocks) {
-      ArrayRef<unsigned> IncomingValues = P.second;
-      if (IncomingValues.size() <= 1)
+      if (P.getSecond().size() <= 1)
         continue;
-      unsigned BasicI = IncomingValues.front();
-      for (unsigned I : IncomingValues.drop_front()) {
+      unsigned BasicI = P.getSecond().front();
+      for (unsigned I : ArrayRef(P.getSecond()).drop_front()) {
         assert(all_of(enumerate(Operands[I]),
                       [&](const auto &Data) {
                         return !Data.value() ||