Revert "[LoadStoreVectorizer] Postprocess and merge equivalence classes" (#119657)

Reverts #114501, due to the following failure:
https://lab.llvm.org/buildbot/#/builders/55/builds/4171

Author: michalpaszkowski

llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp

@@ -324,11 +324,6 @@ class Vectorizer {
       Instruction *ChainElem, Instruction *ChainBegin,
       const DenseMap<Instruction *, APInt /*OffsetFromLeader*/> &ChainOffsets);
 
-  /// Merges the equivalence classes if they have underlying objects that differ
-  /// by one level of indirection (i.e., one is a getelementptr and the other is
-  /// the base pointer in that getelementptr).
-  void mergeEquivalenceClasses(EquivalenceClassMap &EQClasses) const;
-
   /// Collects loads and stores grouped by "equivalence class", where:
   ///   - all elements in an eq class are a load or all are a store,
   ///   - they all load/store the same element size (it's OK to have e.g. i8 and
@@ -1310,123 +1305,6 @@ std::optional<APInt> Vectorizer::getConstantOffsetSelects(
   return std::nullopt;
 }
 
-void Vectorizer::mergeEquivalenceClasses(EquivalenceClassMap &EQClasses) const {
-  if (EQClasses.size() < 2) // There is nothing to merge.
-    return;
-
-  // The reduced key has all elements of the ECClassKey except the underlying
-  // object. Check that EqClassKey has 4 elements and define the reduced key.
-  static_assert(std::tuple_size_v<EqClassKey> == 4,
-                "EqClassKey has changed - EqClassReducedKey needs changes too");
-  using EqClassReducedKey =
-      std::tuple<std::tuple_element_t<1, EqClassKey> /* AddrSpace */,
-                 std::tuple_element_t<2, EqClassKey> /* Element size */,
-                 std::tuple_element_t<3, EqClassKey> /* IsLoad; */>;
-  using ECReducedKeyToUnderlyingObjectMap =
-      MapVector<EqClassReducedKey,
-                SmallPtrSet<std::tuple_element_t<0, EqClassKey>, 4>>;
-
-  // Form a map from the reduced key (without the underlying object) to the
-  // underlying objects: 1 reduced key to many underlying objects, to form
-  // groups of potentially merge-able equivalence classes.
-  ECReducedKeyToUnderlyingObjectMap RedKeyToUOMap;
-  bool FoundPotentiallyOptimizableEC = false;
-  for (const auto &EC : EQClasses) {
-    const auto &Key = EC.first;
-    EqClassReducedKey RedKey{std::get<1>(Key), std::get<2>(Key),
-                             std::get<3>(Key)};
-    RedKeyToUOMap[RedKey].insert(std::get<0>(Key));
-    if (RedKeyToUOMap[RedKey].size() > 1)
-      FoundPotentiallyOptimizableEC = true;
-  }
-  if (!FoundPotentiallyOptimizableEC)
-    return;
-
-  LLVM_DEBUG({
-    dbgs() << "LSV: mergeEquivalenceClasses: before merging:\n";
-    for (const auto &EC : EQClasses) {
-      dbgs() << "    Key: ([" << std::get<0>(EC.first)
-             << "]: " << *std::get<0>(EC.first) << ", " << std::get<1>(EC.first)
-             << ", " << std::get<2>(EC.first) << ", "
-             << static_cast<int>(std::get<3>(EC.first)) << ")\n";
-      for (const auto &Inst : EC.second)
-        dbgs() << "\tInst: " << *Inst << '\n';
-    }
-  });
-  LLVM_DEBUG({
-    dbgs() << "LSV: mergeEquivalenceClasses: RedKeyToUOMap:\n";
-    for (const auto &RedKeyToUO : RedKeyToUOMap) {
-      dbgs() << "    Reduced key: (" << std::get<0>(RedKeyToUO.first) << ", "
-             << std::get<1>(RedKeyToUO.first) << ", "
-             << static_cast<int>(std::get<2>(RedKeyToUO.first)) << ") --> "
-             << RedKeyToUO.second.size() << " underlying objects:\n";
-      for (auto UObject : RedKeyToUO.second)
-        dbgs() << "    [" << UObject << "]: " << *UObject << '\n';
-    }
-  });
-
-  using UObjectToUObjectMap = DenseMap<const Value *, const Value *>;
-
-  // Compute the ultimate targets for a set of underlying objects.
-  auto GetUltimateTargets =
-      [](SmallPtrSetImpl<const Value *> &UObjects) -> UObjectToUObjectMap {
-    UObjectToUObjectMap IndirectionMap;
-    for (const auto *UObject : UObjects) {
-      const unsigned MaxLookupDepth = 1; // look for 1-level indirections only
-      const auto *UltimateTarget = getUnderlyingObject(UObject, MaxLookupDepth);
-      if (UltimateTarget != UObject)
-        IndirectionMap[UObject] = UltimateTarget;
-    }
-    UObjectToUObjectMap UltimateTargetsMap;
-    for (const auto *UObject : UObjects) {
-      auto Target = UObject;
-      auto It = IndirectionMap.find(Target);
-      for (; It != IndirectionMap.end(); It = IndirectionMap.find(Target))
-        Target = It->second;
-      UltimateTargetsMap[UObject] = Target;
-    }
-    return UltimateTargetsMap;
-  };
-
-  // For each item in RedKeyToUOMap, if it has more than one underlying object,
-  // try to merge the equivalence classes.
-  for (auto &[RedKey, UObjects] : RedKeyToUOMap) {
-    if (UObjects.size() < 2)
-      continue;
-    auto UTMap = GetUltimateTargets(UObjects);
-    for (const auto &[UObject, UltimateTarget] : UTMap) {
-      if (UObject == UltimateTarget)
-        continue;
-
-      EqClassKey KeyFrom{UObject, std::get<0>(RedKey), std::get<1>(RedKey),
-                         std::get<2>(RedKey)};
-      EqClassKey KeyTo{UltimateTarget, std::get<0>(RedKey), std::get<1>(RedKey),
-                       std::get<2>(RedKey)};
-      const auto &VecFrom = EQClasses[KeyFrom];
-      const auto &VecTo = EQClasses[KeyTo];
-      SmallVector<Instruction *, 8> MergedVec;
-      std::merge(VecFrom.begin(), VecFrom.end(), VecTo.begin(), VecTo.end(),
-                 std::back_inserter(MergedVec),
-                 [](Instruction *A, Instruction *B) {
-                   return A && B && A->comesBefore(B);
-                 });
-      EQClasses[KeyTo] = std::move(MergedVec);
-      EQClasses.erase(KeyFrom);
-    }
-  }
-  LLVM_DEBUG({
-    dbgs() << "LSV: mergeEquivalenceClasses: after merging:\n";
-    for (const auto &EC : EQClasses) {
-      dbgs() << "    Key: ([" << std::get<0>(EC.first)
-             << "]: " << *std::get<0>(EC.first) << ", " << std::get<1>(EC.first)
-             << ", " << std::get<2>(EC.first) << ", "
-             << static_cast<int>(std::get<3>(EC.first)) << ")\n";
-      for (const auto &Inst : EC.second)
-        dbgs() << "\tInst: " << *Inst << '\n';
-    }
-  });
-}
-
 EquivalenceClassMap
 Vectorizer::collectEquivalenceClasses(BasicBlock::iterator Begin,
                                       BasicBlock::iterator End) {
@@ -1499,7 +1377,6 @@ Vectorizer::collectEquivalenceClasses(BasicBlock::iterator Begin,
         .emplace_back(&I);
   }
 
-  mergeEquivalenceClasses(Ret);
   return Ret;
 }