diff --git a/llvm/lib/Analysis/MemorySSA.cpp b/llvm/lib/Analysis/MemorySSA.cpp
new file mode 100644
index 0000000..9101705
--- /dev/null
+++ b/llvm/lib/Analysis/MemorySSA.cpp
@@ -0,0 +1,2059 @@
+//===-- MemorySSA.cpp - Memory SSA Builder---------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------===//
+//
+// This file implements the MemorySSA class.
+//
+//===----------------------------------------------------------------===//
+#include "llvm/Analysis/MemorySSA.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/DepthFirstIterator.h"
+#include "llvm/ADT/GraphTraits.h"
+#include "llvm/ADT/PostOrderIterator.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallBitVector.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/CFG.h"
+#include "llvm/Analysis/GlobalsModRef.h"
+#include "llvm/Analysis/IteratedDominanceFrontier.h"
+#include "llvm/Analysis/MemoryLocation.h"
+#include "llvm/Analysis/PHITransAddr.h"
+#include "llvm/IR/AssemblyAnnotationWriter.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Metadata.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/PatternMatch.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/FormattedStream.h"
+#include "llvm/Transforms/Scalar.h"
+#include <algorithm>
+
+#define DEBUG_TYPE "memoryssa"
+using namespace llvm;
+INITIALIZE_PASS_BEGIN(MemorySSAWrapperPass, "memoryssa", "Memory SSA", false,
+                      true)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
+INITIALIZE_PASS_END(MemorySSAWrapperPass, "memoryssa", "Memory SSA", false,
+                    true)
+
+INITIALIZE_PASS_BEGIN(MemorySSAPrinterLegacyPass, "print-memoryssa",
+                      "Memory SSA Printer", false, false)
+INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
+INITIALIZE_PASS_END(MemorySSAPrinterLegacyPass, "print-memoryssa",
+                    "Memory SSA Printer", false, false)
+
+static cl::opt<unsigned> MaxCheckLimit(
+    "memssa-check-limit", cl::Hidden, cl::init(100),
+    cl::desc("The maximum number of stores/phis MemorySSA"
+             "will consider trying to walk past (default = 100)"));
+
+static cl::opt<bool>
+    VerifyMemorySSA("verify-memoryssa", cl::init(false), cl::Hidden,
+                    cl::desc("Verify MemorySSA in legacy printer pass."));
+
+namespace llvm {
+/// \brief An assembly annotator class to print Memory SSA information in
+/// comments.
+class MemorySSAAnnotatedWriter : public AssemblyAnnotationWriter {
+  friend class MemorySSA;
+  const MemorySSA *MSSA;
+
+public:
+  MemorySSAAnnotatedWriter(const MemorySSA *M) : MSSA(M) {}
+
+  virtual void emitBasicBlockStartAnnot(const BasicBlock *BB,
+                                        formatted_raw_ostream &OS) {
+    if (MemoryAccess *MA = MSSA->getMemoryAccess(BB))
+      OS << "; " << *MA << "\n";
+  }
+
+  virtual void emitInstructionAnnot(const Instruction *I,
+                                    formatted_raw_ostream &OS) {
+    if (MemoryAccess *MA = MSSA->getMemoryAccess(I))
+      OS << "; " << *MA << "\n";
+  }
+};
+}
+
+namespace {
+/// Our current alias analysis API differentiates heavily between calls and
+/// non-calls, and functions called on one usually assert on the other.
+/// This class encapsulates the distinction to simplify other code that wants
+/// "Memory affecting instructions and related data" to use as a key.
+/// For example, this class is used as a densemap key in the use optimizer.
+class MemoryLocOrCall {
+public:
+  MemoryLocOrCall() : IsCall(false) {}
+  MemoryLocOrCall(MemoryUseOrDef *MUD)
+      : MemoryLocOrCall(MUD->getMemoryInst()) {}
+  MemoryLocOrCall(const MemoryUseOrDef *MUD)
+      : MemoryLocOrCall(MUD->getMemoryInst()) {}
+
+  MemoryLocOrCall(Instruction *Inst) {
+    if (ImmutableCallSite(Inst)) {
+      IsCall = true;
+      CS = ImmutableCallSite(Inst);
+    } else {
+      IsCall = false;
+      // There is no such thing as a memorylocation for a fence inst, and it is
+      // unique in that regard.
+      if (!isa<FenceInst>(Inst))
+        Loc = MemoryLocation::get(Inst);
+    }
+  }
+
+  explicit MemoryLocOrCall(const MemoryLocation &Loc)
+      : IsCall(false), Loc(Loc) {}
+
+  bool IsCall;
+  ImmutableCallSite getCS() const {
+    assert(IsCall);
+    return CS;
+  }
+  MemoryLocation getLoc() const {
+    assert(!IsCall);
+    return Loc;
+  }
+
+  bool operator==(const MemoryLocOrCall &Other) const {
+    if (IsCall != Other.IsCall)
+      return false;
+
+    if (IsCall)
+      return CS.getCalledValue() == Other.CS.getCalledValue();
+    return Loc == Other.Loc;
+  }
+
+private:
+  union {
+    ImmutableCallSite CS;
+    MemoryLocation Loc;
+  };
+};
+}
+
+namespace llvm {
+template <> struct DenseMapInfo<MemoryLocOrCall> {
+  static inline MemoryLocOrCall getEmptyKey() {
+    return MemoryLocOrCall(DenseMapInfo<MemoryLocation>::getEmptyKey());
+  }
+  static inline MemoryLocOrCall getTombstoneKey() {
+    return MemoryLocOrCall(DenseMapInfo<MemoryLocation>::getTombstoneKey());
+  }
+  static unsigned getHashValue(const MemoryLocOrCall &MLOC) {
+    if (MLOC.IsCall)
+      return hash_combine(MLOC.IsCall,
+                          DenseMapInfo<const Value *>::getHashValue(
+                              MLOC.getCS().getCalledValue()));
+    return hash_combine(
+        MLOC.IsCall, DenseMapInfo<MemoryLocation>::getHashValue(MLOC.getLoc()));
+  }
+  static bool isEqual(const MemoryLocOrCall &LHS, const MemoryLocOrCall &RHS) {
+    return LHS == RHS;
+  }
+};
+
+enum class Reorderability { Always, IfNoAlias, Never };
+
+/// This does one-way checks to see if Use could theoretically be hoisted above
+/// MayClobber. This will not check the other way around.
+///
+/// This assumes that, for the purposes of MemorySSA, Use comes directly after
+/// MayClobber, with no potentially clobbering operations in between them.
+/// (Where potentially clobbering ops are memory barriers, aliased stores, etc.)
+static Reorderability getLoadReorderability(const LoadInst *Use,
+                                            const LoadInst *MayClobber) {
+  bool VolatileUse = Use->isVolatile();
+  bool VolatileClobber = MayClobber->isVolatile();
+  // Volatile operations may never be reordered with other volatile operations.
+  if (VolatileUse && VolatileClobber)
+    return Reorderability::Never;
+
+  // The lang ref allows reordering of volatile and non-volatile operations.
+  // Whether an aliasing nonvolatile load and volatile load can be reordered,
+  // though, is ambiguous. Because it may not be best to exploit this ambiguity,
+  // we only allow volatile/non-volatile reordering if the volatile and
+  // non-volatile operations don't alias.
+  Reorderability Result = VolatileUse || VolatileClobber
+                              ? Reorderability::IfNoAlias
+                              : Reorderability::Always;
+
+  // If a load is seq_cst, it cannot be moved above other loads. If its ordering
+  // is weaker, it can be moved above other loads. We just need to be sure that
+  // MayClobber isn't an acquire load, because loads can't be moved above
+  // acquire loads.
+  //
+  // Note that this explicitly *does* allow the free reordering of monotonic (or
+  // weaker) loads of the same address.
+  bool SeqCstUse = Use->getOrdering() == AtomicOrdering::SequentiallyConsistent;
+  bool MayClobberIsAcquire = isAtLeastOrStrongerThan(MayClobber->getOrdering(),
+                                                     AtomicOrdering::Acquire);
+  if (SeqCstUse || MayClobberIsAcquire)
+    return Reorderability::Never;
+  return Result;
+}
+
+static bool instructionClobbersQuery(MemoryDef *MD,
+                                     const MemoryLocation &UseLoc,
+                                     const Instruction *UseInst,
+                                     AliasAnalysis &AA) {
+  Instruction *DefInst = MD->getMemoryInst();
+  assert(DefInst && "Defining instruction not actually an instruction");
+  ImmutableCallSite UseCS(UseInst);
+
+  if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(DefInst)) {
+    // These intrinsics will show up as affecting memory, but they are just
+    // markers.
+    switch (II->getIntrinsicID()) {
+    case Intrinsic::lifetime_start:
+      if (UseCS)
+        return false;
+      return AA.isMustAlias(MemoryLocation(II->getArgOperand(1)), UseLoc);
+    case Intrinsic::lifetime_end:
+    case Intrinsic::invariant_start:
+    case Intrinsic::invariant_end:
+    case Intrinsic::assume:
+      return false;
+    default:
+      break;
+    }
+  }
+
+  if (UseCS) {
+    ModRefInfo I = AA.getModRefInfo(DefInst, UseCS);
+    return I != MRI_NoModRef;
+  }
+
+  if (auto *DefLoad = dyn_cast<LoadInst>(DefInst)) {
+    if (auto *UseLoad = dyn_cast<LoadInst>(UseInst)) {
+      switch (getLoadReorderability(UseLoad, DefLoad)) {
+      case Reorderability::Always:
+        return false;
+      case Reorderability::Never:
+        return true;
+      case Reorderability::IfNoAlias:
+        return !AA.isNoAlias(UseLoc, MemoryLocation::get(DefLoad));
+      }
+    }
+  }
+
+  return AA.getModRefInfo(DefInst, UseLoc) & MRI_Mod;
+}
+
+static bool instructionClobbersQuery(MemoryDef *MD, const MemoryUseOrDef *MU,
+                                     const MemoryLocOrCall &UseMLOC,
+                                     AliasAnalysis &AA) {
+  // FIXME: This is a temporary hack to allow a single instructionClobbersQuery
+  // to exist while MemoryLocOrCall is pushed through places.
+  if (UseMLOC.IsCall)
+    return instructionClobbersQuery(MD, MemoryLocation(), MU->getMemoryInst(),
+                                    AA);
+  return instructionClobbersQuery(MD, UseMLOC.getLoc(), MU->getMemoryInst(),
+                                  AA);
+}
+
+// Return true when MD may alias MU, return false otherwise.
+bool MemorySSAUtil::defClobbersUseOrDef(MemoryDef *MD, const MemoryUseOrDef *MU,
+                                        AliasAnalysis &AA) {
+  return instructionClobbersQuery(MD, MU, MemoryLocOrCall(MU), AA);
+}
+}
+
+namespace {
+struct UpwardsMemoryQuery {
+  // True if our original query started off as a call
+  bool IsCall;
+  // The pointer location we started the query with. This will be empty if
+  // IsCall is true.
+  MemoryLocation StartingLoc;
+  // This is the instruction we were querying about.
+  const Instruction *Inst;
+  // The MemoryAccess we actually got called with, used to test local domination
+  const MemoryAccess *OriginalAccess;
+
+  UpwardsMemoryQuery()
+      : IsCall(false), Inst(nullptr), OriginalAccess(nullptr) {}
+
+  UpwardsMemoryQuery(const Instruction *Inst, const MemoryAccess *Access)
+      : IsCall(ImmutableCallSite(Inst)), Inst(Inst), OriginalAccess(Access) {
+    if (!IsCall)
+      StartingLoc = MemoryLocation::get(Inst);
+  }
+};
+
+static bool lifetimeEndsAt(MemoryDef *MD, const MemoryLocation &Loc,
+                           AliasAnalysis &AA) {
+  Instruction *Inst = MD->getMemoryInst();
+  if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
+    switch (II->getIntrinsicID()) {
+    case Intrinsic::lifetime_end:
+      return AA.isMustAlias(MemoryLocation(II->getArgOperand(1)), Loc);
+    default:
+      return false;
+    }
+  }
+  return false;
+}
+
+static bool isUseTriviallyOptimizableToLiveOnEntry(AliasAnalysis &AA,
+                                                   const Instruction *I) {
+  // If the memory can't be changed, then loads of the memory can't be
+  // clobbered.
+  //
+  // FIXME: We should handle invariant groups, as well. It's a bit harder,
+  // because we need to pay close attention to invariant group barriers.
+  return isa<LoadInst>(I) && (I->getMetadata(LLVMContext::MD_invariant_load) ||
+                              AA.pointsToConstantMemory(cast<LoadInst>(I)->
+                                                          getPointerOperand()));
+}
+
+/// Verifies that `Start` is clobbered by `ClobberAt`, and that nothing
+/// inbetween `Start` and `ClobberAt` can clobbers `Start`.
+///
+/// This is meant to be as simple and self-contained as possible. Because it
+/// uses no cache, etc., it can be relatively expensive.
+///
+/// \param Start     The MemoryAccess that we want to walk from.
+/// \param ClobberAt A clobber for Start.
+/// \param StartLoc  The MemoryLocation for Start.
+/// \param MSSA      The MemorySSA isntance that Start and ClobberAt belong to.
+/// \param Query     The UpwardsMemoryQuery we used for our search.
+/// \param AA        The AliasAnalysis we used for our search.
+static void LLVM_ATTRIBUTE_UNUSED
+checkClobberSanity(MemoryAccess *Start, MemoryAccess *ClobberAt,
+                   const MemoryLocation &StartLoc, const MemorySSA &MSSA,
+                   const UpwardsMemoryQuery &Query, AliasAnalysis &AA) {
+  assert(MSSA.dominates(ClobberAt, Start) && "Clobber doesn't dominate start?");
+
+  if (MSSA.isLiveOnEntryDef(Start)) {
+    assert(MSSA.isLiveOnEntryDef(ClobberAt) &&
+           "liveOnEntry must clobber itself");
+    return;
+  }
+
+  bool FoundClobber = false;
+  DenseSet<MemoryAccessPair> VisitedPhis;
+  SmallVector<MemoryAccessPair, 8> Worklist;
+  Worklist.emplace_back(Start, StartLoc);
+  // Walk all paths from Start to ClobberAt, while looking for clobbers. If one
+  // is found, complain.
+  while (!Worklist.empty()) {
+    MemoryAccessPair MAP = Worklist.pop_back_val();
+    // All we care about is that nothing from Start to ClobberAt clobbers Start.
+    // We learn nothing from revisiting nodes.
+    if (!VisitedPhis.insert(MAP).second)
+      continue;
+
+    for (MemoryAccess *MA : def_chain(MAP.first)) {
+      if (MA == ClobberAt) {
+        if (auto *MD = dyn_cast<MemoryDef>(MA)) {
+          // instructionClobbersQuery isn't essentially free, so don't use `|=`,
+          // since it won't let us short-circuit.
+          //
+          // Also, note that this can't be hoisted out of the `Worklist` loop,
+          // since MD may only act as a clobber for 1 of N MemoryLocations.
+          FoundClobber =
+              FoundClobber || MSSA.isLiveOnEntryDef(MD) ||
+              instructionClobbersQuery(MD, MAP.second, Query.Inst, AA);
+        }
+        break;
+      }
+
+      // We should never hit liveOnEntry, unless it's the clobber.
+      assert(!MSSA.isLiveOnEntryDef(MA) && "Hit liveOnEntry before clobber?");
+
+      if (auto *MD = dyn_cast<MemoryDef>(MA)) {
+        (void)MD;
+        assert(!instructionClobbersQuery(MD, MAP.second, Query.Inst, AA) &&
+               "Found clobber before reaching ClobberAt!");
+        continue;
+      }
+
+      assert(isa<MemoryPhi>(MA));
+      Worklist.append(upward_defs_begin({MA, MAP.second}), upward_defs_end());
+    }
+  }
+
+  // If ClobberAt is a MemoryPhi, we can assume something above it acted as a
+  // clobber. Otherwise, `ClobberAt` should've acted as a clobber at some point.
+  assert((isa<MemoryPhi>(ClobberAt) || FoundClobber) &&
+         "ClobberAt never acted as a clobber");
+}
+
+/// Our algorithm for walking (and trying to optimize) clobbers, all wrapped up
+/// in one class.
+class ClobberWalker {
+  /// Save a few bytes by using unsigned instead of size_t.
+  using ListIndex = unsigned;
+
+  /// Represents a span of contiguous MemoryDefs, potentially ending in a
+  /// MemoryPhi.
+  struct DefPath {
+    MemoryLocation Loc;
+    // Note that, because we always walk in reverse, Last will always dominate
+    // First. Also note that First and Last are inclusive.
+    MemoryAccess *First;
+    MemoryAccess *Last;
+    Optional<ListIndex> Previous;
+
+    DefPath(const MemoryLocation &Loc, MemoryAccess *First, MemoryAccess *Last,
+            Optional<ListIndex> Previous)
+        : Loc(Loc), First(First), Last(Last), Previous(Previous) {}
+
+    DefPath(const MemoryLocation &Loc, MemoryAccess *Init,
+            Optional<ListIndex> Previous)
+        : DefPath(Loc, Init, Init, Previous) {}
+  };
+
+  const MemorySSA &MSSA;
+  AliasAnalysis &AA;
+  DominatorTree &DT;
+  UpwardsMemoryQuery *Query;
+
+  // Phi optimization bookkeeping
+  SmallVector<DefPath, 32> Paths;
+  DenseSet<ConstMemoryAccessPair> VisitedPhis;
+
+  /// Find the nearest def or phi that `From` can legally be optimized to.
+  const MemoryAccess *getWalkTarget(const MemoryPhi *From) const {
+    assert(From->getNumOperands() && "Phi with no operands?");
+
+    BasicBlock *BB = From->getBlock();
+    MemoryAccess *Result = MSSA.getLiveOnEntryDef();
+    DomTreeNode *Node = DT.getNode(BB);
+    while ((Node = Node->getIDom())) {
+      auto *Defs = MSSA.getBlockDefs(Node->getBlock());
+      if (Defs)
+        return &*Defs->rbegin();
+    }
+    return Result;
+  }
+
+  /// Result of calling walkToPhiOrClobber.
+  struct UpwardsWalkResult {
+    /// The "Result" of the walk. Either a clobber, the last thing we walked, or
+    /// both.
+    MemoryAccess *Result;
+    bool IsKnownClobber;
+  };
+
+  /// Walk to the next Phi or Clobber in the def chain starting at Desc.Last.
+  /// This will update Desc.Last as it walks. It will (optionally) also stop at
+  /// StopAt.
+  ///
+  /// This does not test for whether StopAt is a clobber
+  UpwardsWalkResult
+  walkToPhiOrClobber(DefPath &Desc,
+                     const MemoryAccess *StopAt = nullptr) const {
+    assert(!isa<MemoryUse>(Desc.Last) && "Uses don't exist in my world");
+
+    for (MemoryAccess *Current : def_chain(Desc.Last)) {
+      Desc.Last = Current;
+      if (Current == StopAt)
+        return {Current, false};
+
+      if (auto *MD = dyn_cast<MemoryDef>(Current))
+        if (MSSA.isLiveOnEntryDef(MD) ||
+            instructionClobbersQuery(MD, Desc.Loc, Query->Inst, AA))
+          return {MD, true};
+    }
+
+    assert(isa<MemoryPhi>(Desc.Last) &&
+           "Ended at a non-clobber that's not a phi?");
+    return {Desc.Last, false};
+  }
+
+  void addSearches(MemoryPhi *Phi, SmallVectorImpl<ListIndex> &PausedSearches,
+                   ListIndex PriorNode) {
+    auto UpwardDefs = make_range(upward_defs_begin({Phi, Paths[PriorNode].Loc}),
+                                 upward_defs_end());
+    for (const MemoryAccessPair &P : UpwardDefs) {
+      PausedSearches.push_back(Paths.size());
+      Paths.emplace_back(P.second, P.first, PriorNode);
+    }
+  }
+
+  /// Represents a search that terminated after finding a clobber. This clobber
+  /// may or may not be present in the path of defs from LastNode..SearchStart,
+  /// since it may have been retrieved from cache.
+  struct TerminatedPath {
+    MemoryAccess *Clobber;
+    ListIndex LastNode;
+  };
+
+  /// Get an access that keeps us from optimizing to the given phi.
+  ///
+  /// PausedSearches is an array of indices into the Paths array. Its incoming
+  /// value is the indices of searches that stopped at the last phi optimization
+  /// target. It's left in an unspecified state.
+  ///
+  /// If this returns None, NewPaused is a vector of searches that terminated
+  /// at StopWhere. Otherwise, NewPaused is left in an unspecified state.
+  Optional<TerminatedPath>
+  getBlockingAccess(const MemoryAccess *StopWhere,
+                    SmallVectorImpl<ListIndex> &PausedSearches,
+                    SmallVectorImpl<ListIndex> &NewPaused,
+                    SmallVectorImpl<TerminatedPath> &Terminated) {
+    assert(!PausedSearches.empty() && "No searches to continue?");
+
+    // BFS vs DFS really doesn't make a difference here, so just do a DFS with
+    // PausedSearches as our stack.
+    while (!PausedSearches.empty()) {
+      ListIndex PathIndex = PausedSearches.pop_back_val();
+      DefPath &Node = Paths[PathIndex];
+
+      // If we've already visited this path with this MemoryLocation, we don't
+      // need to do so again.
+      //
+      // NOTE: That we just drop these paths on the ground makes caching
+      // behavior sporadic. e.g. given a diamond:
+      //  A
+      // B C
+      //  D
+      //
+      // ...If we walk D, B, A, C, we'll only cache the result of phi
+      // optimization for A, B, and D; C will be skipped because it dies here.
+      // This arguably isn't the worst thing ever, since:
+      //   - We generally query things in a top-down order, so if we got below D
+      //     without needing cache entries for {C, MemLoc}, then chances are
+      //     that those cache entries would end up ultimately unused.
+      //   - We still cache things for A, so C only needs to walk up a bit.
+      // If this behavior becomes problematic, we can fix without a ton of extra
+      // work.
+      if (!VisitedPhis.insert({Node.Last, Node.Loc}).second)
+        continue;
+
+      UpwardsWalkResult Res = walkToPhiOrClobber(Node, /*StopAt=*/StopWhere);
+      if (Res.IsKnownClobber) {
+        assert(Res.Result != StopWhere);
+        // If this wasn't a cache hit, we hit a clobber when walking. That's a
+        // failure.
+        TerminatedPath Term{Res.Result, PathIndex};
+        if (!MSSA.dominates(Res.Result, StopWhere))
+          return Term;
+
+        // Otherwise, it's a valid thing to potentially optimize to.
+        Terminated.push_back(Term);
+        continue;
+      }
+
+      if (Res.Result == StopWhere) {
+        // We've hit our target. Save this path off for if we want to continue
+        // walking.
+        NewPaused.push_back(PathIndex);
+        continue;
+      }
+
+      assert(!MSSA.isLiveOnEntryDef(Res.Result) && "liveOnEntry is a clobber");
+      addSearches(cast<MemoryPhi>(Res.Result), PausedSearches, PathIndex);
+    }
+
+    return None;
+  }
+
+  template <typename T, typename Walker>
+  struct generic_def_path_iterator
+      : public iterator_facade_base<generic_def_path_iterator<T, Walker>,
+                                    std::forward_iterator_tag, T *> {
+    generic_def_path_iterator() : W(nullptr), N(None) {}
+    generic_def_path_iterator(Walker *W, ListIndex N) : W(W), N(N) {}
+
+    T &operator*() const { return curNode(); }
+
+    generic_def_path_iterator &operator++() {
+      N = curNode().Previous;
+      return *this;
+    }
+
+    bool operator==(const generic_def_path_iterator &O) const {
+      if (N.hasValue() != O.N.hasValue())
+        return false;
+      return !N.hasValue() || *N == *O.N;
+    }
+
+  private:
+    T &curNode() const { return W->Paths[*N]; }
+
+    Walker *W;
+    Optional<ListIndex> N;
+  };
+
+  using def_path_iterator = generic_def_path_iterator<DefPath, ClobberWalker>;
+  using const_def_path_iterator =
+      generic_def_path_iterator<const DefPath, const ClobberWalker>;
+
+  iterator_range<def_path_iterator> def_path(ListIndex From) {
+    return make_range(def_path_iterator(this, From), def_path_iterator());
+  }
+
+  iterator_range<const_def_path_iterator> const_def_path(ListIndex From) const {
+    return make_range(const_def_path_iterator(this, From),
+                      const_def_path_iterator());
+  }
+
+  struct OptznResult {
+    /// The path that contains our result.
+    TerminatedPath PrimaryClobber;
+    /// The paths that we can legally cache back from, but that aren't
+    /// necessarily the result of the Phi optimization.
+    SmallVector<TerminatedPath, 4> OtherClobbers;
+  };
+
+  ListIndex defPathIndex(const DefPath &N) const {
+    // The assert looks nicer if we don't need to do &N
+    const DefPath *NP = &N;
+    assert(!Paths.empty() && NP >= &Paths.front() && NP <= &Paths.back() &&
+           "Out of bounds DefPath!");
+    return NP - &Paths.front();
+  }
+
+  /// Try to optimize a phi as best as we can. Returns a SmallVector of Paths
+  /// that act as legal clobbers. Note that this won't return *all* clobbers.
+  ///
+  /// Phi optimization algorithm tl;dr:
+  ///   - Find the earliest def/phi, A, we can optimize to
+  ///   - Find if all paths from the starting memory access ultimately reach A
+  ///     - If not, optimization isn't possible.
+  ///     - Otherwise, walk from A to another clobber or phi, A'.
+  ///       - If A' is a def, we're done.
+  ///       - If A' is a phi, try to optimize it.
+  ///
+  /// A path is a series of {MemoryAccess, MemoryLocation} pairs. A path
+  /// terminates when a MemoryAccess that clobbers said MemoryLocation is found.
+  OptznResult tryOptimizePhi(MemoryPhi *Phi, MemoryAccess *Start,
+                             const MemoryLocation &Loc) {
+    assert(Paths.empty() && VisitedPhis.empty() &&
+           "Reset the optimization state.");
+
+    Paths.emplace_back(Loc, Start, Phi, None);
+    // Stores how many "valid" optimization nodes we had prior to calling
+    // addSearches/getBlockingAccess. Necessary for caching if we had a blocker.
+    auto PriorPathsSize = Paths.size();
+
+    SmallVector<ListIndex, 16> PausedSearches;
+    SmallVector<ListIndex, 8> NewPaused;
+    SmallVector<TerminatedPath, 4> TerminatedPaths;
+
+    addSearches(Phi, PausedSearches, 0);
+
+    // Moves the TerminatedPath with the "most dominated" Clobber to the end of
+    // Paths.
+    auto MoveDominatedPathToEnd = [&](SmallVectorImpl<TerminatedPath> &Paths) {
+      assert(!Paths.empty() && "Need a path to move");
+      auto Dom = Paths.begin();
+      for (auto I = std::next(Dom), E = Paths.end(); I != E; ++I)
+        if (!MSSA.dominates(I->Clobber, Dom->Clobber))
+          Dom = I;
+      auto Last = Paths.end() - 1;
+      if (Last != Dom)
+        std::iter_swap(Last, Dom);
+    };
+
+    MemoryPhi *Current = Phi;
+    while (1) {
+      assert(!MSSA.isLiveOnEntryDef(Current) &&
+             "liveOnEntry wasn't treated as a clobber?");
+
+      const auto *Target = getWalkTarget(Current);
+      // If a TerminatedPath doesn't dominate Target, then it wasn't a legal
+      // optimization for the prior phi.
+      assert(all_of(TerminatedPaths, [&](const TerminatedPath &P) {
+        return MSSA.dominates(P.Clobber, Target);
+      }));
+
+      // FIXME: This is broken, because the Blocker may be reported to be
+      // liveOnEntry, and we'll happily wait for that to disappear (read: never)
+      // For the moment, this is fine, since we do nothing with blocker info.
+      if (Optional<TerminatedPath> Blocker = getBlockingAccess(
+              Target, PausedSearches, NewPaused, TerminatedPaths)) {
+
+        // Find the node we started at. We can't search based on N->Last, since
+        // we may have gone around a loop with a different MemoryLocation.
+        auto Iter = find_if(def_path(Blocker->LastNode), [&](const DefPath &N) {
+          return defPathIndex(N) < PriorPathsSize;
+        });
+        assert(Iter != def_path_iterator());
+
+        DefPath &CurNode = *Iter;
+        assert(CurNode.Last == Current);
+
+        // Two things:
+        // A. We can't reliably cache all of NewPaused back. Consider a case
+        //    where we have two paths in NewPaused; one of which can't optimize
+        //    above this phi, whereas the other can. If we cache the second path
+        //    back, we'll end up with suboptimal cache entries. We can handle
+        //    cases like this a bit better when we either try to find all
+        //    clobbers that block phi optimization, or when our cache starts
+        //    supporting unfinished searches.
+        // B. We can't reliably cache TerminatedPaths back here without doing
+        //    extra checks; consider a case like:
+        //       T
+        //      / \
+        //     D   C
+        //      \ /
+        //       S
+        //    Where T is our target, C is a node with a clobber on it, D is a
+        //    diamond (with a clobber *only* on the left or right node, N), and
+        //    S is our start. Say we walk to D, through the node opposite N
+        //    (read: ignoring the clobber), and see a cache entry in the top
+        //    node of D. That cache entry gets put into TerminatedPaths. We then
+        //    walk up to C (N is later in our worklist), find the clobber, and
+        //    quit. If we append TerminatedPaths to OtherClobbers, we'll cache
+        //    the bottom part of D to the cached clobber, ignoring the clobber
+        //    in N. Again, this problem goes away if we start tracking all
+        //    blockers for a given phi optimization.
+        TerminatedPath Result{CurNode.Last, defPathIndex(CurNode)};
+        return {Result, {}};
+      }
+
+      // If there's nothing left to search, then all paths led to valid clobbers
+      // that we got from our cache; pick the nearest to the start, and allow
+      // the rest to be cached back.
+      if (NewPaused.empty()) {
+        MoveDominatedPathToEnd(TerminatedPaths);
+        TerminatedPath Result = TerminatedPaths.pop_back_val();
+        return {Result, std::move(TerminatedPaths)};
+      }
+
+      MemoryAccess *DefChainEnd = nullptr;
+      SmallVector<TerminatedPath, 4> Clobbers;
+      for (ListIndex Paused : NewPaused) {
+        UpwardsWalkResult WR = walkToPhiOrClobber(Paths[Paused]);
+        if (WR.IsKnownClobber)
+          Clobbers.push_back({WR.Result, Paused});
+        else
+          // Micro-opt: If we hit the end of the chain, save it.
+          DefChainEnd = WR.Result;
+      }
+
+      if (!TerminatedPaths.empty()) {
+        // If we couldn't find the dominating phi/liveOnEntry in the above loop,
+        // do it now.
+        if (!DefChainEnd)
+          for (auto *MA : def_chain(const_cast<MemoryAccess *>(Target)))
+            DefChainEnd = MA;
+
+        // If any of the terminated paths don't dominate the phi we'll try to
+        // optimize, we need to figure out what they are and quit.
+        const BasicBlock *ChainBB = DefChainEnd->getBlock();
+        for (const TerminatedPath &TP : TerminatedPaths) {
+          // Because we know that DefChainEnd is as "high" as we can go, we
+          // don't need local dominance checks; BB dominance is sufficient.
+          if (DT.dominates(ChainBB, TP.Clobber->getBlock()))
+            Clobbers.push_back(TP);
+        }
+      }
+
+      // If we have clobbers in the def chain, find the one closest to Current
+      // and quit.
+      if (!Clobbers.empty()) {
+        MoveDominatedPathToEnd(Clobbers);
+        TerminatedPath Result = Clobbers.pop_back_val();
+        return {Result, std::move(Clobbers)};
+      }
+
+      assert(all_of(NewPaused,
+                    [&](ListIndex I) { return Paths[I].Last == DefChainEnd; }));
+
+      // Because liveOnEntry is a clobber, this must be a phi.
+      auto *DefChainPhi = cast<MemoryPhi>(DefChainEnd);
+
+      PriorPathsSize = Paths.size();
+      PausedSearches.clear();
+      for (ListIndex I : NewPaused)
+        addSearches(DefChainPhi, PausedSearches, I);
+      NewPaused.clear();
+
+      Current = DefChainPhi;
+    }
+  }
+
+  void verifyOptResult(const OptznResult &R) const {
+    assert(all_of(R.OtherClobbers, [&](const TerminatedPath &P) {
+      return MSSA.dominates(P.Clobber, R.PrimaryClobber.Clobber);
+    }));
+  }
+
+  void resetPhiOptznState() {
+    Paths.clear();
+    VisitedPhis.clear();
+  }
+
+public:
+  ClobberWalker(const MemorySSA &MSSA, AliasAnalysis &AA, DominatorTree &DT)
+      : MSSA(MSSA), AA(AA), DT(DT) {}
+
+  void reset() {}
+
+  /// Finds the nearest clobber for the given query, optimizing phis if
+  /// possible.
+  MemoryAccess *findClobber(MemoryAccess *Start, UpwardsMemoryQuery &Q) {
+    Query = &Q;
+
+    MemoryAccess *Current = Start;
+    // This walker pretends uses don't exist. If we're handed one, silently grab
+    // its def. (This has the nice side-effect of ensuring we never cache uses)
+    if (auto *MU = dyn_cast<MemoryUse>(Start))
+      Current = MU->getDefiningAccess();
+
+    DefPath FirstDesc(Q.StartingLoc, Current, Current, None);
+    // Fast path for the overly-common case (no crazy phi optimization
+    // necessary)
+    UpwardsWalkResult WalkResult = walkToPhiOrClobber(FirstDesc);
+    MemoryAccess *Result;
+    if (WalkResult.IsKnownClobber) {
+      Result = WalkResult.Result;
+    } else {
+      OptznResult OptRes = tryOptimizePhi(cast<MemoryPhi>(FirstDesc.Last),
+                                          Current, Q.StartingLoc);
+      verifyOptResult(OptRes);
+      resetPhiOptznState();
+      Result = OptRes.PrimaryClobber.Clobber;
+    }
+
+#ifdef EXPENSIVE_CHECKS
+    checkClobberSanity(Current, Result, Q.StartingLoc, MSSA, Q, AA);
+#endif
+    return Result;
+  }
+
+  void verify(const MemorySSA *MSSA) { assert(MSSA == &this->MSSA); }
+};
+
+struct RenamePassData {
+  DomTreeNode *DTN;
+  DomTreeNode::const_iterator ChildIt;
+  MemoryAccess *IncomingVal;
+
+  RenamePassData(DomTreeNode *D, DomTreeNode::const_iterator It,
+                 MemoryAccess *M)
+      : DTN(D), ChildIt(It), IncomingVal(M) {}
+  void swap(RenamePassData &RHS) {
+    std::swap(DTN, RHS.DTN);
+    std::swap(ChildIt, RHS.ChildIt);
+    std::swap(IncomingVal, RHS.IncomingVal);
+  }
+};
+} // anonymous namespace
+
+namespace llvm {
+/// \brief A MemorySSAWalker that does AA walks to disambiguate accesses. It no
+/// longer does caching on its own,
+/// but the name has been retained for the moment.
+class MemorySSA::CachingWalker final : public MemorySSAWalker {
+  ClobberWalker Walker;
+  bool AutoResetWalker;
+
+  MemoryAccess *getClobberingMemoryAccess(MemoryAccess *, UpwardsMemoryQuery &);
+  void verifyRemoved(MemoryAccess *);
+
+public:
+  CachingWalker(MemorySSA *, AliasAnalysis *, DominatorTree *);
+  ~CachingWalker() override;
+
+  using MemorySSAWalker::getClobberingMemoryAccess;
+  MemoryAccess *getClobberingMemoryAccess(MemoryAccess *) override;
+  MemoryAccess *getClobberingMemoryAccess(MemoryAccess *,
+                                          const MemoryLocation &) override;
+  void invalidateInfo(MemoryAccess *) override;
+
+  /// Whether we call resetClobberWalker() after each time we *actually* walk to
+  /// answer a clobber query.
+  void setAutoResetWalker(bool AutoReset) { AutoResetWalker = AutoReset; }
+
+  /// Drop the walker's persistent data structures.
+  void resetClobberWalker() { Walker.reset(); }
+
+  void verify(const MemorySSA *MSSA) override {
+    MemorySSAWalker::verify(MSSA);
+    Walker.verify(MSSA);
+  }
+};
+
+void MemorySSA::renameSuccessorPhis(BasicBlock *BB, MemoryAccess *IncomingVal,
+                                    bool RenameAllUses) {
+  // Pass through values to our successors
+  for (const BasicBlock *S : successors(BB)) {
+    auto It = PerBlockAccesses.find(S);
+    // Rename the phi nodes in our successor block
+    if (It == PerBlockAccesses.end() || !isa<MemoryPhi>(It->second->front()))
+      continue;
+    AccessList *Accesses = It->second.get();
+    auto *Phi = cast<MemoryPhi>(&Accesses->front());
+    if (RenameAllUses) {
+      int PhiIndex = Phi->getBasicBlockIndex(BB);
+      assert(PhiIndex != -1 && "Incomplete phi during partial rename");
+      Phi->setIncomingValue(PhiIndex, IncomingVal);
+    } else
+      Phi->addIncoming(IncomingVal, BB);
+  }
+}
+
+/// \brief Rename a single basic block into MemorySSA form.
+/// Uses the standard SSA renaming algorithm.
+/// \returns The new incoming value.
+MemoryAccess *MemorySSA::renameBlock(BasicBlock *BB, MemoryAccess *IncomingVal,
+                                     bool RenameAllUses) {
+  auto It = PerBlockAccesses.find(BB);
+  // Skip most processing if the list is empty.
+  if (It != PerBlockAccesses.end()) {
+    AccessList *Accesses = It->second.get();
+    for (MemoryAccess &L : *Accesses) {
+      if (MemoryUseOrDef *MUD = dyn_cast<MemoryUseOrDef>(&L)) {
+        if (MUD->getDefiningAccess() == nullptr || RenameAllUses)
+          MUD->setDefiningAccess(IncomingVal);
+        if (isa<MemoryDef>(&L))
+          IncomingVal = &L;
+      } else {
+        IncomingVal = &L;
+      }
+    }
+  }
+  return IncomingVal;
+}
+
+/// \brief This is the standard SSA renaming algorithm.
+///
+/// We walk the dominator tree in preorder, renaming accesses, and then filling
+/// in phi nodes in our successors.
+void MemorySSA::renamePass(DomTreeNode *Root, MemoryAccess *IncomingVal,
+                           SmallPtrSetImpl<BasicBlock *> &Visited,
+                           bool SkipVisited, bool RenameAllUses) {
+  SmallVector<RenamePassData, 32> WorkStack;
+  // Skip everything if we already renamed this block and we are skipping.
+  // Note: You can't sink this into the if, because we need it to occur
+  // regardless of whether we skip blocks or not.
+  bool AlreadyVisited = !Visited.insert(Root->getBlock()).second;
+  if (SkipVisited && AlreadyVisited)
+    return;
+
+  IncomingVal = renameBlock(Root->getBlock(), IncomingVal, RenameAllUses);
+  renameSuccessorPhis(Root->getBlock(), IncomingVal, RenameAllUses);
+  WorkStack.push_back({Root, Root->begin(), IncomingVal});
+
+  while (!WorkStack.empty()) {
+    DomTreeNode *Node = WorkStack.back().DTN;
+    DomTreeNode::const_iterator ChildIt = WorkStack.back().ChildIt;
+    IncomingVal = WorkStack.back().IncomingVal;
+
+    if (ChildIt == Node->end()) {
+      WorkStack.pop_back();
+    } else {
+      DomTreeNode *Child = *ChildIt;
+      ++WorkStack.back().ChildIt;
+      BasicBlock *BB = Child->getBlock();
+      // Note: You can't sink this into the if, because we need it to occur
+      // regardless of whether we skip blocks or not.
+      AlreadyVisited = !Visited.insert(BB).second;
+      if (SkipVisited && AlreadyVisited) {
+        // We already visited this during our renaming, which can happen when
+        // being asked to rename multiple blocks. Figure out the incoming val,
+        // which is the last def.
+        // Incoming value can only change if there is a block def, and in that
+        // case, it's the last block def in the list.
+        if (auto *BlockDefs = getWritableBlockDefs(BB))
+          IncomingVal = &*BlockDefs->rbegin();
+      } else
+        IncomingVal = renameBlock(BB, IncomingVal, RenameAllUses);
+      renameSuccessorPhis(BB, IncomingVal, RenameAllUses);
+      WorkStack.push_back({Child, Child->begin(), IncomingVal});
+    }
+  }
+}
+
+/// \brief This handles unreachable block accesses by deleting phi nodes in
+/// unreachable blocks, and marking all other unreachable MemoryAccess's as
+/// being uses of the live on entry definition.
+void MemorySSA::markUnreachableAsLiveOnEntry(BasicBlock *BB) {
+  assert(!DT->isReachableFromEntry(BB) &&
+         "Reachable block found while handling unreachable blocks");
+
+  // Make sure phi nodes in our reachable successors end up with a
+  // LiveOnEntryDef for our incoming edge, even though our block is forward
+  // unreachable.  We could just disconnect these blocks from the CFG fully,
+  // but we do not right now.
+  for (const BasicBlock *S : successors(BB)) {
+    if (!DT->isReachableFromEntry(S))
+      continue;
+    auto It = PerBlockAccesses.find(S);
+    // Rename the phi nodes in our successor block
+    if (It == PerBlockAccesses.end() || !isa<MemoryPhi>(It->second->front()))
+      continue;
+    AccessList *Accesses = It->second.get();
+    auto *Phi = cast<MemoryPhi>(&Accesses->front());
+    Phi->addIncoming(LiveOnEntryDef.get(), BB);
+  }
+
+  auto It = PerBlockAccesses.find(BB);
+  if (It == PerBlockAccesses.end())
+    return;
+
+  auto &Accesses = It->second;
+  for (auto AI = Accesses->begin(), AE = Accesses->end(); AI != AE;) {
+    auto Next = std::next(AI);
+    // If we have a phi, just remove it. We are going to replace all
+    // users with live on entry.
+    if (auto *UseOrDef = dyn_cast<MemoryUseOrDef>(AI))
+      UseOrDef->setDefiningAccess(LiveOnEntryDef.get());
+    else
+      Accesses->erase(AI);
+    AI = Next;
+  }
+}
+
+MemorySSA::MemorySSA(Function &Func, AliasAnalysis *AA, DominatorTree *DT)
+    : AA(AA), DT(DT), F(Func), LiveOnEntryDef(nullptr), Walker(nullptr),
+      NextID(INVALID_MEMORYACCESS_ID) {
+  buildMemorySSA();
+}
+
+MemorySSA::~MemorySSA() {
+  // Drop all our references
+  for (const auto &Pair : PerBlockAccesses)
+    for (MemoryAccess &MA : *Pair.second)
+      MA.dropAllReferences();
+}
+
+MemorySSA::AccessList *MemorySSA::getOrCreateAccessList(const BasicBlock *BB) {
+  auto Res = PerBlockAccesses.insert(std::make_pair(BB, nullptr));
+
+  if (Res.second)
+    Res.first->second = make_unique<AccessList>();
+  return Res.first->second.get();
+}
+MemorySSA::DefsList *MemorySSA::getOrCreateDefsList(const BasicBlock *BB) {
+  auto Res = PerBlockDefs.insert(std::make_pair(BB, nullptr));
+
+  if (Res.second)
+    Res.first->second = make_unique<DefsList>();
+  return Res.first->second.get();
+}
+
+/// This class is a batch walker of all MemoryUse's in the program, and points
+/// their defining access at the thing that actually clobbers them.  Because it
+/// is a batch walker that touches everything, it does not operate like the
+/// other walkers.  This walker is basically performing a top-down SSA renaming
+/// pass, where the version stack is used as the cache.  This enables it to be
+/// significantly more time and memory efficient than using the regular walker,
+/// which is walking bottom-up.
+class MemorySSA::OptimizeUses {
+public:
+  OptimizeUses(MemorySSA *MSSA, MemorySSAWalker *Walker, AliasAnalysis *AA,
+               DominatorTree *DT)
+      : MSSA(MSSA), Walker(Walker), AA(AA), DT(DT) {
+    Walker = MSSA->getWalker();
+  }
+
+  void optimizeUses();
+
+private:
+  /// This represents where a given memorylocation is in the stack.
+  struct MemlocStackInfo {
+    // This essentially is keeping track of versions of the stack. Whenever
+    // the stack changes due to pushes or pops, these versions increase.
+    unsigned long StackEpoch;
+    unsigned long PopEpoch;
+    // This is the lower bound of places on the stack to check. It is equal to
+    // the place the last stack walk ended.
+    // Note: Correctness depends on this being initialized to 0, which densemap
+    // does
+    unsigned long LowerBound;
+    const BasicBlock *LowerBoundBlock;
+    // This is where the last walk for this memory location ended.
+    unsigned long LastKill;
+    bool LastKillValid;
+  };
+  void optimizeUsesInBlock(const BasicBlock *, unsigned long &, unsigned long &,
+                           SmallVectorImpl<MemoryAccess *> &,
+                           DenseMap<MemoryLocOrCall, MemlocStackInfo> &);
+  MemorySSA *MSSA;
+  MemorySSAWalker *Walker;
+  AliasAnalysis *AA;
+  DominatorTree *DT;
+};
+
+/// Optimize the uses in a given block This is basically the SSA renaming
+/// algorithm, with one caveat: We are able to use a single stack for all
+/// MemoryUses.  This is because the set of *possible* reaching MemoryDefs is
+/// the same for every MemoryUse.  The *actual* clobbering MemoryDef is just
+/// going to be some position in that stack of possible ones.
+///
+/// We track the stack positions that each MemoryLocation needs
+/// to check, and last ended at.  This is because we only want to check the
+/// things that changed since last time.  The same MemoryLocation should
+/// get clobbered by the same store (getModRefInfo does not use invariantness or
+/// things like this, and if they start, we can modify MemoryLocOrCall to
+/// include relevant data)
+void MemorySSA::OptimizeUses::optimizeUsesInBlock(
+    const BasicBlock *BB, unsigned long &StackEpoch, unsigned long &PopEpoch,
+    SmallVectorImpl<MemoryAccess *> &VersionStack,
+    DenseMap<MemoryLocOrCall, MemlocStackInfo> &LocStackInfo) {
+
+  /// If no accesses, nothing to do.
+  MemorySSA::AccessList *Accesses = MSSA->getWritableBlockAccesses(BB);
+  if (Accesses == nullptr)
+    return;
+
+  // Pop everything that doesn't dominate the current block off the stack,
+  // increment the PopEpoch to account for this.
+  while (true) {
+    assert(
+        !VersionStack.empty() &&
+        "Version stack should have liveOnEntry sentinel dominating everything");
+    BasicBlock *BackBlock = VersionStack.back()->getBlock();
+    if (DT->dominates(BackBlock, BB))
+      break;
+    while (VersionStack.back()->getBlock() == BackBlock)
+      VersionStack.pop_back();
+    ++PopEpoch;
+  }
+
+  for (MemoryAccess &MA : *Accesses) {
+    auto *MU = dyn_cast<MemoryUse>(&MA);
+    if (!MU) {
+      VersionStack.push_back(&MA);
+      ++StackEpoch;
+      continue;
+    }
+
+    if (isUseTriviallyOptimizableToLiveOnEntry(*AA, MU->getMemoryInst())) {
+      MU->setDefiningAccess(MSSA->getLiveOnEntryDef(), true);
+      continue;
+    }
+
+    MemoryLocOrCall UseMLOC(MU);
+    auto &LocInfo = LocStackInfo[UseMLOC];
+    // If the pop epoch changed, it means we've removed stuff from top of
+    // stack due to changing blocks. We may have to reset the lower bound or
+    // last kill info.
+    if (LocInfo.PopEpoch != PopEpoch) {
+      LocInfo.PopEpoch = PopEpoch;
+      LocInfo.StackEpoch = StackEpoch;
+      // If the lower bound was in something that no longer dominates us, we
+      // have to reset it.
+      // We can't simply track stack size, because the stack may have had
+      // pushes/pops in the meantime.
+      // XXX: This is non-optimal, but only is slower cases with heavily
+      // branching dominator trees.  To get the optimal number of queries would
+      // be to make lowerbound and lastkill a per-loc stack, and pop it until
+      // the top of that stack dominates us.  This does not seem worth it ATM.
+      // A much cheaper optimization would be to always explore the deepest
+      // branch of the dominator tree first. This will guarantee this resets on
+      // the smallest set of blocks.
+      if (LocInfo.LowerBoundBlock && LocInfo.LowerBoundBlock != BB &&
+          !DT->dominates(LocInfo.LowerBoundBlock, BB)) {
+        // Reset the lower bound of things to check.
+        // TODO: Some day we should be able to reset to last kill, rather than
+        // 0.
+        LocInfo.LowerBound = 0;
+        LocInfo.LowerBoundBlock = VersionStack[0]->getBlock();
+        LocInfo.LastKillValid = false;
+      }
+    } else if (LocInfo.StackEpoch != StackEpoch) {
+      // If all that has changed is the StackEpoch, we only have to check the
+      // new things on the stack, because we've checked everything before.  In
+      // this case, the lower bound of things to check remains the same.
+      LocInfo.PopEpoch = PopEpoch;
+      LocInfo.StackEpoch = StackEpoch;
+    }
+    if (!LocInfo.LastKillValid) {
+      LocInfo.LastKill = VersionStack.size() - 1;
+      LocInfo.LastKillValid = true;
+    }
+
+    // At this point, we should have corrected last kill and LowerBound to be
+    // in bounds.
+    assert(LocInfo.LowerBound < VersionStack.size() &&
+           "Lower bound out of range");
+    assert(LocInfo.LastKill < VersionStack.size() &&
+           "Last kill info out of range");
+    // In any case, the new upper bound is the top of the stack.
+    unsigned long UpperBound = VersionStack.size() - 1;
+
+    if (UpperBound - LocInfo.LowerBound > MaxCheckLimit) {
+      DEBUG(dbgs() << "MemorySSA skipping optimization of " << *MU << " ("
+                   << *(MU->getMemoryInst()) << ")"
+                   << " because there are " << UpperBound - LocInfo.LowerBound
+                   << " stores to disambiguate\n");
+      // Because we did not walk, LastKill is no longer valid, as this may
+      // have been a kill.
+      LocInfo.LastKillValid = false;
+      continue;
+    }
+    bool FoundClobberResult = false;
+    while (UpperBound > LocInfo.LowerBound) {
+      if (isa<MemoryPhi>(VersionStack[UpperBound])) {
+        // For phis, use the walker, see where we ended up, go there
+        Instruction *UseInst = MU->getMemoryInst();
+        MemoryAccess *Result = Walker->getClobberingMemoryAccess(UseInst);
+        // We are guaranteed to find it or something is wrong
+        while (VersionStack[UpperBound] != Result) {
+          assert(UpperBound != 0);
+          --UpperBound;
+        }
+        FoundClobberResult = true;
+        break;
+      }
+
+      MemoryDef *MD = cast<MemoryDef>(VersionStack[UpperBound]);
+      // If the lifetime of the pointer ends at this instruction, it's live on
+      // entry.
+      if (!UseMLOC.IsCall && lifetimeEndsAt(MD, UseMLOC.getLoc(), *AA)) {
+        // Reset UpperBound to liveOnEntryDef's place in the stack
+        UpperBound = 0;
+        FoundClobberResult = true;
+        break;
+      }
+      if (instructionClobbersQuery(MD, MU, UseMLOC, *AA)) {
+        FoundClobberResult = true;
+        break;
+      }
+      --UpperBound;
+    }
+    // At the end of this loop, UpperBound is either a clobber, or lower bound
+    // PHI walking may cause it to be < LowerBound, and in fact, < LastKill.
+    if (FoundClobberResult || UpperBound < LocInfo.LastKill) {
+      MU->setDefiningAccess(VersionStack[UpperBound], true);
+      // We were last killed now by where we got to
+      LocInfo.LastKill = UpperBound;
+    } else {
+      // Otherwise, we checked all the new ones, and now we know we can get to
+      // LastKill.
+      MU->setDefiningAccess(VersionStack[LocInfo.LastKill], true);
+    }
+    LocInfo.LowerBound = VersionStack.size() - 1;
+    LocInfo.LowerBoundBlock = BB;
+  }
+}
+
+/// Optimize uses to point to their actual clobbering definitions.
+void MemorySSA::OptimizeUses::optimizeUses() {
+  SmallVector<MemoryAccess *, 16> VersionStack;
+  DenseMap<MemoryLocOrCall, MemlocStackInfo> LocStackInfo;
+  VersionStack.push_back(MSSA->getLiveOnEntryDef());
+
+  unsigned long StackEpoch = 1;
+  unsigned long PopEpoch = 1;
+  // We perform a non-recursive top-down dominator tree walk.
+  for (const auto *DomNode : depth_first(DT->getRootNode()))
+    optimizeUsesInBlock(DomNode->getBlock(), StackEpoch, PopEpoch, VersionStack,
+                        LocStackInfo);
+}
+
+void MemorySSA::placePHINodes(
+    const SmallPtrSetImpl<BasicBlock *> &DefiningBlocks,
+    const DenseMap<const BasicBlock *, unsigned int> &BBNumbers) {
+  // Determine where our MemoryPhi's should go
+  ForwardIDFCalculator IDFs(*DT);
+  IDFs.setDefiningBlocks(DefiningBlocks);
+  SmallVector<BasicBlock *, 32> IDFBlocks;
+  IDFs.calculate(IDFBlocks);
+
+  std::sort(IDFBlocks.begin(), IDFBlocks.end(),
+            [&BBNumbers](const BasicBlock *A, const BasicBlock *B) {
+              return BBNumbers.lookup(A) < BBNumbers.lookup(B);
+            });
+
+  // Now place MemoryPhi nodes.
+  for (auto &BB : IDFBlocks)
+    createMemoryPhi(BB);
+}
+
+void MemorySSA::buildMemorySSA() {
+  // We create an access to represent "live on entry", for things like
+  // arguments or users of globals, where the memory they use is defined before
+  // the beginning of the function. We do not actually insert it into the IR.
+  // We do not define a live on exit for the immediate uses, and thus our
+  // semantics do *not* imply that something with no immediate uses can simply
+  // be removed.
+  BasicBlock &StartingPoint = F.getEntryBlock();
+  LiveOnEntryDef = make_unique<MemoryDef>(F.getContext(), nullptr, nullptr,
+                                          &StartingPoint, NextID++);
+  DenseMap<const BasicBlock *, unsigned int> BBNumbers;
+  unsigned NextBBNum = 0;
+
+  // We maintain lists of memory accesses per-block, trading memory for time. We
+  // could just look up the memory access for every possible instruction in the
+  // stream.
+  SmallPtrSet<BasicBlock *, 32> DefiningBlocks;
+  SmallPtrSet<BasicBlock *, 32> DefUseBlocks;
+  // Go through each block, figure out where defs occur, and chain together all
+  // the accesses.
+  for (BasicBlock &B : F) {
+    BBNumbers[&B] = NextBBNum++;
+    bool InsertIntoDef = false;
+    AccessList *Accesses = nullptr;
+    DefsList *Defs = nullptr;
+    for (Instruction &I : B) {
+      MemoryUseOrDef *MUD = createNewAccess(&I);
+      if (!MUD)
+        continue;
+
+      if (!Accesses)
+        Accesses = getOrCreateAccessList(&B);
+      Accesses->push_back(MUD);
+      if (isa<MemoryDef>(MUD)) {
+        InsertIntoDef = true;
+        if (!Defs)
+          Defs = getOrCreateDefsList(&B);
+        Defs->push_back(*MUD);
+      }
+    }
+    if (InsertIntoDef)
+      DefiningBlocks.insert(&B);
+    if (Accesses)
+      DefUseBlocks.insert(&B);
+  }
+  placePHINodes(DefiningBlocks, BBNumbers);
+
+  // Now do regular SSA renaming on the MemoryDef/MemoryUse. Visited will get
+  // filled in with all blocks.
+  SmallPtrSet<BasicBlock *, 16> Visited;
+  renamePass(DT->getRootNode(), LiveOnEntryDef.get(), Visited);
+
+  CachingWalker *Walker = getWalkerImpl();
+
+  // We're doing a batch of updates; don't drop useful caches between them.
+  Walker->setAutoResetWalker(false);
+  OptimizeUses(this, Walker, AA, DT).optimizeUses();
+  Walker->setAutoResetWalker(true);
+  Walker->resetClobberWalker();
+
+  // Mark the uses in unreachable blocks as live on entry, so that they go
+  // somewhere.
+  for (auto &BB : F)
+    if (!Visited.count(&BB))
+      markUnreachableAsLiveOnEntry(&BB);
+}
+
+MemorySSAWalker *MemorySSA::getWalker() { return getWalkerImpl(); }
+
+MemorySSA::CachingWalker *MemorySSA::getWalkerImpl() {
+  if (Walker)
+    return Walker.get();
+
+  Walker = make_unique<CachingWalker>(this, AA, DT);
+  return Walker.get();
+}
+
+// This is a helper function used by the creation routines. It places NewAccess
+// into the access and defs lists for a given basic block, at the given
+// insertion point.
+void MemorySSA::insertIntoListsForBlock(MemoryAccess *NewAccess,
+                                        const BasicBlock *BB,
+                                        InsertionPlace Point) {
+  auto *Accesses = getOrCreateAccessList(BB);
+  if (Point == Beginning) {
+    // If it's a phi node, it goes first, otherwise, it goes after any phi
+    // nodes.
+    if (isa<MemoryPhi>(NewAccess)) {
+      Accesses->push_front(NewAccess);
+      auto *Defs = getOrCreateDefsList(BB);
+      Defs->push_front(*NewAccess);
+    } else {
+      auto AI = find_if_not(
+          *Accesses, [](const MemoryAccess &MA) { return isa<MemoryPhi>(MA); });
+      Accesses->insert(AI, NewAccess);
+      if (!isa<MemoryUse>(NewAccess)) {
+        auto *Defs = getOrCreateDefsList(BB);
+        auto DI = find_if_not(
+            *Defs, [](const MemoryAccess &MA) { return isa<MemoryPhi>(MA); });
+        Defs->insert(DI, *NewAccess);
+      }
+    }
+  } else {
+    Accesses->push_back(NewAccess);
+    if (!isa<MemoryUse>(NewAccess)) {
+      auto *Defs = getOrCreateDefsList(BB);
+      Defs->push_back(*NewAccess);
+    }
+  }
+  BlockNumberingValid.erase(BB);
+}
+
+void MemorySSA::insertIntoListsBefore(MemoryAccess *What, const BasicBlock *BB,
+                                      AccessList::iterator InsertPt) {
+  auto *Accesses = getWritableBlockAccesses(BB);
+  bool WasEnd = InsertPt == Accesses->end();
+  Accesses->insert(AccessList::iterator(InsertPt), What);
+  if (!isa<MemoryUse>(What)) {
+    auto *Defs = getOrCreateDefsList(BB);
+    // If we got asked to insert at the end, we have an easy job, just shove it
+    // at the end. If we got asked to insert before an existing def, we also get
+    // an terator. If we got asked to insert before a use, we have to hunt for
+    // the next def.
+    if (WasEnd) {
+      Defs->push_back(*What);
+    } else if (isa<MemoryDef>(InsertPt)) {
+      Defs->insert(InsertPt->getDefsIterator(), *What);
+    } else {
+      while (InsertPt != Accesses->end() && !isa<MemoryDef>(InsertPt))
+        ++InsertPt;
+      // Either we found a def, or we are inserting at the end
+      if (InsertPt == Accesses->end())
+        Defs->push_back(*What);
+      else
+        Defs->insert(InsertPt->getDefsIterator(), *What);
+    }
+  }
+  BlockNumberingValid.erase(BB);
+}
+
+// Move What before Where in the IR.  The end result is taht What will belong to
+// the right lists and have the right Block set, but will not otherwise be
+// correct. It will not have the right defining access, and if it is a def,
+// things below it will not properly be updated.
+void MemorySSA::moveTo(MemoryUseOrDef *What, BasicBlock *BB,
+                       AccessList::iterator Where) {
+  // Keep it in the lookup tables, remove from the lists
+  removeFromLists(What, false);
+  What->setBlock(BB);
+  insertIntoListsBefore(What, BB, Where);
+}
+
+void MemorySSA::moveTo(MemoryUseOrDef *What, BasicBlock *BB,
+                       InsertionPlace Point) {
+  removeFromLists(What, false);
+  What->setBlock(BB);
+  insertIntoListsForBlock(What, BB, Point);
+}
+
+MemoryPhi *MemorySSA::createMemoryPhi(BasicBlock *BB) {
+  assert(!getMemoryAccess(BB) && "MemoryPhi already exists for this BB");
+  MemoryPhi *Phi = new MemoryPhi(BB->getContext(), BB, NextID++);
+  // Phi's always are placed at the front of the block.
+  insertIntoListsForBlock(Phi, BB, Beginning);
+  ValueToMemoryAccess[BB] = Phi;
+  return Phi;
+}
+
+MemoryUseOrDef *MemorySSA::createDefinedAccess(Instruction *I,
+                                               MemoryAccess *Definition) {
+  assert(!isa<PHINode>(I) && "Cannot create a defined access for a PHI");
+  MemoryUseOrDef *NewAccess = createNewAccess(I);
+  assert(
+      NewAccess != nullptr &&
+      "Tried to create a memory access for a non-memory touching instruction");
+  NewAccess->setDefiningAccess(Definition);
+  return NewAccess;
+}
+
+// Return true if the instruction has ordering constraints.
+// Note specifically that this only considers stores and loads
+// because others are still considered ModRef by getModRefInfo.
+static inline bool isOrdered(const Instruction *I) {
+  if (auto *SI = dyn_cast<StoreInst>(I)) {
+    if (!SI->isUnordered())
+      return true;
+  } else if (auto *LI = dyn_cast<LoadInst>(I)) {
+    if (!LI->isUnordered())
+      return true;
+  }
+  return false;
+}
+/// \brief Helper function to create new memory accesses
+MemoryUseOrDef *MemorySSA::createNewAccess(Instruction *I) {
+  // The assume intrinsic has a control dependency which we model by claiming
+  // that it writes arbitrarily. Ignore that fake memory dependency here.
+  // FIXME: Replace this special casing with a more accurate modelling of
+  // assume's control dependency.
+  if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
+    if (II->getIntrinsicID() == Intrinsic::assume)
+      return nullptr;
+
+  // Find out what affect this instruction has on memory.
+  ModRefInfo ModRef = AA->getModRefInfo(I);
+  // The isOrdered check is used to ensure that volatiles end up as defs
+  // (atomics end up as ModRef right now anyway).  Until we separate the
+  // ordering chain from the memory chain, this enables people to see at least
+  // some relative ordering to volatiles.  Note that getClobberingMemoryAccess
+  // will still give an answer that bypasses other volatile loads.  TODO:
+  // Separate memory aliasing and ordering into two different chains so that we
+  // can precisely represent both "what memory will this read/write/is clobbered
+  // by" and "what instructions can I move this past".
+  bool Def = bool(ModRef & MRI_Mod) || isOrdered(I);
+  bool Use = bool(ModRef & MRI_Ref);
+
+  // It's possible for an instruction to not modify memory at all. During
+  // construction, we ignore them.
+  if (!Def && !Use)
+    return nullptr;
+
+  assert((Def || Use) &&
+         "Trying to create a memory access with a non-memory instruction");
+
+  MemoryUseOrDef *MUD;
+  if (Def)
+    MUD = new MemoryDef(I->getContext(), nullptr, I, I->getParent(), NextID++);
+  else
+    MUD = new MemoryUse(I->getContext(), nullptr, I, I->getParent());
+  ValueToMemoryAccess[I] = MUD;
+  return MUD;
+}
+
+/// \brief Returns true if \p Replacer dominates \p Replacee .
+bool MemorySSA::dominatesUse(const MemoryAccess *Replacer,
+                             const MemoryAccess *Replacee) const {
+  if (isa<MemoryUseOrDef>(Replacee))
+    return DT->dominates(Replacer->getBlock(), Replacee->getBlock());
+  const auto *MP = cast<MemoryPhi>(Replacee);
+  // For a phi node, the use occurs in the predecessor block of the phi node.
+  // Since we may occur multiple times in the phi node, we have to check each
+  // operand to ensure Replacer dominates each operand where Replacee occurs.
+  for (const Use &Arg : MP->operands()) {
+    if (Arg.get() != Replacee &&
+        !DT->dominates(Replacer->getBlock(), MP->getIncomingBlock(Arg)))
+      return false;
+  }
+  return true;
+}
+
+/// \brief Properly remove \p MA from all of MemorySSA's lookup tables.
+void MemorySSA::removeFromLookups(MemoryAccess *MA) {
+  assert(MA->use_empty() &&
+         "Trying to remove memory access that still has uses");
+  BlockNumbering.erase(MA);
+  if (MemoryUseOrDef *MUD = dyn_cast<MemoryUseOrDef>(MA))
+    MUD->setDefiningAccess(nullptr);
+  // Invalidate our walker's cache if necessary
+  if (!isa<MemoryUse>(MA))
+    Walker->invalidateInfo(MA);
+  // The call below to erase will destroy MA, so we can't change the order we
+  // are doing things here
+  Value *MemoryInst;
+  if (MemoryUseOrDef *MUD = dyn_cast<MemoryUseOrDef>(MA)) {
+    MemoryInst = MUD->getMemoryInst();
+  } else {
+    MemoryInst = MA->getBlock();
+  }
+  auto VMA = ValueToMemoryAccess.find(MemoryInst);
+  if (VMA->second == MA)
+    ValueToMemoryAccess.erase(VMA);
+}
+
+/// \brief Properly remove \p MA from all of MemorySSA's lists.
+///
+/// Because of the way the intrusive list and use lists work, it is important to
+/// do removal in the right order.
+/// ShouldDelete defaults to true, and will cause the memory access to also be
+/// deleted, not just removed.
+void MemorySSA::removeFromLists(MemoryAccess *MA, bool ShouldDelete) {
+  // The access list owns the reference, so we erase it from the non-owning list
+  // first.
+  if (!isa<MemoryUse>(MA)) {
+    auto DefsIt = PerBlockDefs.find(MA->getBlock());
+    std::unique_ptr<DefsList> &Defs = DefsIt->second;
+    Defs->remove(*MA);
+    if (Defs->empty())
+      PerBlockDefs.erase(DefsIt);
+  }
+
+  // The erase call here will delete it. If we don't want it deleted, we call
+  // remove instead.
+  auto AccessIt = PerBlockAccesses.find(MA->getBlock());
+  std::unique_ptr<AccessList> &Accesses = AccessIt->second;
+  if (ShouldDelete)
+    Accesses->erase(MA);
+  else
+    Accesses->remove(MA);
+
+  if (Accesses->empty())
+    PerBlockAccesses.erase(AccessIt);
+}
+
+void MemorySSA::print(raw_ostream &OS) const {
+  MemorySSAAnnotatedWriter Writer(this);
+  F.print(OS, &Writer);
+}
+
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+LLVM_DUMP_METHOD void MemorySSA::dump() const { print(dbgs()); }
+#endif
+
+void MemorySSA::verifyMemorySSA() const {
+  verifyDefUses(F);
+  verifyDomination(F);
+  verifyOrdering(F);
+  Walker->verify(this);
+}
+
+/// \brief Verify that the order and existence of MemoryAccesses matches the
+/// order and existence of memory affecting instructions.
+void MemorySSA::verifyOrdering(Function &F) const {
+  // Walk all the blocks, comparing what the lookups think and what the access
+  // lists think, as well as the order in the blocks vs the order in the access
+  // lists.
+  SmallVector<MemoryAccess *, 32> ActualAccesses;
+  SmallVector<MemoryAccess *, 32> ActualDefs;
+  for (BasicBlock &B : F) {
+    const AccessList *AL = getBlockAccesses(&B);
+    const auto *DL = getBlockDefs(&B);
+    MemoryAccess *Phi = getMemoryAccess(&B);
+    if (Phi) {
+      ActualAccesses.push_back(Phi);
+      ActualDefs.push_back(Phi);
+    }
+
+    for (Instruction &I : B) {
+      MemoryAccess *MA = getMemoryAccess(&I);
+      assert((!MA || (AL && (isa<MemoryUse>(MA) || DL))) &&
+             "We have memory affecting instructions "
+             "in this block but they are not in the "
+             "access list or defs list");
+      if (MA) {
+        ActualAccesses.push_back(MA);
+        if (isa<MemoryDef>(MA))
+          ActualDefs.push_back(MA);
+      }
+    }
+    // Either we hit the assert, really have no accesses, or we have both
+    // accesses and an access list.
+    // Same with defs.
+    if (!AL && !DL)
+      continue;
+    assert(AL->size() == ActualAccesses.size() &&
+           "We don't have the same number of accesses in the block as on the "
+           "access list");
+    assert((DL || ActualDefs.size() == 0) &&
+           "Either we should have a defs list, or we should have no defs");
+    assert((!DL || DL->size() == ActualDefs.size()) &&
+           "We don't have the same number of defs in the block as on the "
+           "def list");
+    auto ALI = AL->begin();
+    auto AAI = ActualAccesses.begin();
+    while (ALI != AL->end() && AAI != ActualAccesses.end()) {
+      assert(&*ALI == *AAI && "Not the same accesses in the same order");
+      ++ALI;
+      ++AAI;
+    }
+    ActualAccesses.clear();
+    if (DL) {
+      auto DLI = DL->begin();
+      auto ADI = ActualDefs.begin();
+      while (DLI != DL->end() && ADI != ActualDefs.end()) {
+        assert(&*DLI == *ADI && "Not the same defs in the same order");
+        ++DLI;
+        ++ADI;
+      }
+    }
+    ActualDefs.clear();
+  }
+}
+
+/// \brief Verify the domination properties of MemorySSA by checking that each
+/// definition dominates all of its uses.
+void MemorySSA::verifyDomination(Function &F) const {
+#ifndef NDEBUG
+  for (BasicBlock &B : F) {
+    // Phi nodes are attached to basic blocks
+    if (MemoryPhi *MP = getMemoryAccess(&B))
+      for (const Use &U : MP->uses())
+        assert(dominates(MP, U) && "Memory PHI does not dominate it's uses");
+
+    for (Instruction &I : B) {
+      MemoryAccess *MD = dyn_cast_or_null<MemoryDef>(getMemoryAccess(&I));
+      if (!MD)
+        continue;
+
+      for (const Use &U : MD->uses())
+        assert(dominates(MD, U) && "Memory Def does not dominate it's uses");
+    }
+  }
+#endif
+}
+
+/// \brief Verify the def-use lists in MemorySSA, by verifying that \p Use
+/// appears in the use list of \p Def.
+
+void MemorySSA::verifyUseInDefs(MemoryAccess *Def, MemoryAccess *Use) const {
+#ifndef NDEBUG
+  // The live on entry use may cause us to get a NULL def here
+  if (!Def)
+    assert(isLiveOnEntryDef(Use) &&
+           "Null def but use not point to live on entry def");
+  else
+    assert(is_contained(Def->users(), Use) &&
+           "Did not find use in def's use list");
+#endif
+}
+
+/// \brief Verify the immediate use information, by walking all the memory
+/// accesses and verifying that, for each use, it appears in the
+/// appropriate def's use list
+void MemorySSA::verifyDefUses(Function &F) const {
+  for (BasicBlock &B : F) {
+    // Phi nodes are attached to basic blocks
+    if (MemoryPhi *Phi = getMemoryAccess(&B)) {
+      assert(Phi->getNumOperands() == static_cast<unsigned>(std::distance(
+                                          pred_begin(&B), pred_end(&B))) &&
+             "Incomplete MemoryPhi Node");
+      for (unsigned I = 0, E = Phi->getNumIncomingValues(); I != E; ++I)
+        verifyUseInDefs(Phi->getIncomingValue(I), Phi);
+    }
+
+    for (Instruction &I : B) {
+      if (MemoryUseOrDef *MA = getMemoryAccess(&I)) {
+        verifyUseInDefs(MA->getDefiningAccess(), MA);
+      }
+    }
+  }
+}
+
+MemoryUseOrDef *MemorySSA::getMemoryAccess(const Instruction *I) const {
+  return cast_or_null<MemoryUseOrDef>(ValueToMemoryAccess.lookup(I));
+}
+
+MemoryPhi *MemorySSA::getMemoryAccess(const BasicBlock *BB) const {
+  return cast_or_null<MemoryPhi>(ValueToMemoryAccess.lookup(cast<Value>(BB)));
+}
+
+/// Perform a local numbering on blocks so that instruction ordering can be
+/// determined in constant time.
+/// TODO: We currently just number in order.  If we numbered by N, we could
+/// allow at least N-1 sequences of insertBefore or insertAfter (and at least
+/// log2(N) sequences of mixed before and after) without needing to invalidate
+/// the numbering.
+void MemorySSA::renumberBlock(const BasicBlock *B) const {
+  // The pre-increment ensures the numbers really start at 1.
+  unsigned long CurrentNumber = 0;
+  const AccessList *AL = getBlockAccesses(B);
+  assert(AL != nullptr && "Asking to renumber an empty block");
+  for (const auto &I : *AL)
+    BlockNumbering[&I] = ++CurrentNumber;
+  BlockNumberingValid.insert(B);
+}
+
+/// \brief Determine, for two memory accesses in the same block,
+/// whether \p Dominator dominates \p Dominatee.
+/// \returns True if \p Dominator dominates \p Dominatee.
+bool MemorySSA::locallyDominates(const MemoryAccess *Dominator,
+                                 const MemoryAccess *Dominatee) const {
+
+  const BasicBlock *DominatorBlock = Dominator->getBlock();
+
+  assert((DominatorBlock == Dominatee->getBlock()) &&
+         "Asking for local domination when accesses are in different blocks!");
+  // A node dominates itself.
+  if (Dominatee == Dominator)
+    return true;
+
+  // When Dominatee is defined on function entry, it is not dominated by another
+  // memory access.
+  if (isLiveOnEntryDef(Dominatee))
+    return false;
+
+  // When Dominator is defined on function entry, it dominates the other memory
+  // access.
+  if (isLiveOnEntryDef(Dominator))
+    return true;
+
+  if (!BlockNumberingValid.count(DominatorBlock))
+    renumberBlock(DominatorBlock);
+
+  unsigned long DominatorNum = BlockNumbering.lookup(Dominator);
+  // All numbers start with 1
+  assert(DominatorNum != 0 && "Block was not numbered properly");
+  unsigned long DominateeNum = BlockNumbering.lookup(Dominatee);
+  assert(DominateeNum != 0 && "Block was not numbered properly");
+  return DominatorNum < DominateeNum;
+}
+
+bool MemorySSA::dominates(const MemoryAccess *Dominator,
+                          const MemoryAccess *Dominatee) const {
+  if (Dominator == Dominatee)
+    return true;
+
+  if (isLiveOnEntryDef(Dominatee))
+    return false;
+
+  if (Dominator->getBlock() != Dominatee->getBlock())
+    return DT->dominates(Dominator->getBlock(), Dominatee->getBlock());
+  return locallyDominates(Dominator, Dominatee);
+}
+
+bool MemorySSA::dominates(const MemoryAccess *Dominator,
+                          const Use &Dominatee) const {
+  if (MemoryPhi *MP = dyn_cast<MemoryPhi>(Dominatee.getUser())) {
+    BasicBlock *UseBB = MP->getIncomingBlock(Dominatee);
+    // The def must dominate the incoming block of the phi.
+    if (UseBB != Dominator->getBlock())
+      return DT->dominates(Dominator->getBlock(), UseBB);
+    // If the UseBB and the DefBB are the same, compare locally.
+    return locallyDominates(Dominator, cast<MemoryAccess>(Dominatee));
+  }
+  // If it's not a PHI node use, the normal dominates can already handle it.
+  return dominates(Dominator, cast<MemoryAccess>(Dominatee.getUser()));
+}
+
+const static char LiveOnEntryStr[] = "liveOnEntry";
+
+void MemoryDef::print(raw_ostream &OS) const {
+  MemoryAccess *UO = getDefiningAccess();
+
+  OS << getID() << " = MemoryDef(";
+  if (UO && UO->getID())
+    OS << UO->getID();
+  else
+    OS << LiveOnEntryStr;
+  OS << ')';
+}
+
+void MemoryPhi::print(raw_ostream &OS) const {
+  bool First = true;
+  OS << getID() << " = MemoryPhi(";
+  for (const auto &Op : operands()) {
+    BasicBlock *BB = getIncomingBlock(Op);
+    MemoryAccess *MA = cast<MemoryAccess>(Op);
+    if (!First)
+      OS << ',';
+    else
+      First = false;
+
+    OS << '{';
+    if (BB->hasName())
+      OS << BB->getName();
+    else
+      BB->printAsOperand(OS, false);
+    OS << ',';
+    if (unsigned ID = MA->getID())
+      OS << ID;
+    else
+      OS << LiveOnEntryStr;
+    OS << '}';
+  }
+  OS << ')';
+}
+
+MemoryAccess::~MemoryAccess() {}
+
+void MemoryUse::print(raw_ostream &OS) const {
+  MemoryAccess *UO = getDefiningAccess();
+  OS << "MemoryUse(";
+  if (UO && UO->getID())
+    OS << UO->getID();
+  else
+    OS << LiveOnEntryStr;
+  OS << ')';
+}
+
+void MemoryAccess::dump() const {
+// Cannot completely remove virtual function even in release mode.
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+  print(dbgs());
+  dbgs() << "\n";
+#endif
+}
+
+char MemorySSAPrinterLegacyPass::ID = 0;
+
+MemorySSAPrinterLegacyPass::MemorySSAPrinterLegacyPass() : FunctionPass(ID) {
+  initializeMemorySSAPrinterLegacyPassPass(*PassRegistry::getPassRegistry());
+}
+
+void MemorySSAPrinterLegacyPass::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.setPreservesAll();
+  AU.addRequired<MemorySSAWrapperPass>();
+  AU.addPreserved<MemorySSAWrapperPass>();
+}
+
+bool MemorySSAPrinterLegacyPass::runOnFunction(Function &F) {
+  auto &MSSA = getAnalysis<MemorySSAWrapperPass>().getMSSA();
+  MSSA.print(dbgs());
+  if (VerifyMemorySSA)
+    MSSA.verifyMemorySSA();
+  return false;
+}
+
+AnalysisKey MemorySSAAnalysis::Key;
+
+MemorySSAAnalysis::Result MemorySSAAnalysis::run(Function &F,
+                                                 FunctionAnalysisManager &AM) {
+  auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
+  auto &AA = AM.getResult<AAManager>(F);
+  return MemorySSAAnalysis::Result(make_unique<MemorySSA>(F, &AA, &DT));
+}
+
+PreservedAnalyses MemorySSAPrinterPass::run(Function &F,
+                                            FunctionAnalysisManager &AM) {
+  OS << "MemorySSA for function: " << F.getName() << "\n";
+  AM.getResult<MemorySSAAnalysis>(F).getMSSA().print(OS);
+
+  return PreservedAnalyses::all();
+}
+
+PreservedAnalyses MemorySSAVerifierPass::run(Function &F,
+                                             FunctionAnalysisManager &AM) {
+  AM.getResult<MemorySSAAnalysis>(F).getMSSA().verifyMemorySSA();
+
+  return PreservedAnalyses::all();
+}
+
+char MemorySSAWrapperPass::ID = 0;
+
+MemorySSAWrapperPass::MemorySSAWrapperPass() : FunctionPass(ID) {
+  initializeMemorySSAWrapperPassPass(*PassRegistry::getPassRegistry());
+}
+
+void MemorySSAWrapperPass::releaseMemory() { MSSA.reset(); }
+
+void MemorySSAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.setPreservesAll();
+  AU.addRequiredTransitive<DominatorTreeWrapperPass>();
+  AU.addRequiredTransitive<AAResultsWrapperPass>();
+}
+
+bool MemorySSAWrapperPass::runOnFunction(Function &F) {
+  auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+  auto &AA = getAnalysis<AAResultsWrapperPass>().getAAResults();
+  MSSA.reset(new MemorySSA(F, &AA, &DT));
+  return false;
+}
+
+void MemorySSAWrapperPass::verifyAnalysis() const { MSSA->verifyMemorySSA(); }
+
+void MemorySSAWrapperPass::print(raw_ostream &OS, const Module *M) const {
+  MSSA->print(OS);
+}
+
+MemorySSAWalker::MemorySSAWalker(MemorySSA *M) : MSSA(M) {}
+
+MemorySSA::CachingWalker::CachingWalker(MemorySSA *M, AliasAnalysis *A,
+                                        DominatorTree *D)
+    : MemorySSAWalker(M), Walker(*M, *A, *D), AutoResetWalker(true) {}
+
+MemorySSA::CachingWalker::~CachingWalker() {}
+
+void MemorySSA::CachingWalker::invalidateInfo(MemoryAccess *MA) {
+  if (auto *MUD = dyn_cast<MemoryUseOrDef>(MA))
+    MUD->resetOptimized();
+}
+
+/// \brief Walk the use-def chains starting at \p MA and find
+/// the MemoryAccess that actually clobbers Loc.
+///
+/// \returns our clobbering memory access
+MemoryAccess *MemorySSA::CachingWalker::getClobberingMemoryAccess(
+    MemoryAccess *StartingAccess, UpwardsMemoryQuery &Q) {
+  MemoryAccess *New = Walker.findClobber(StartingAccess, Q);
+#ifdef EXPENSIVE_CHECKS
+  MemoryAccess *NewNoCache = Walker.findClobber(StartingAccess, Q);
+  assert(NewNoCache == New && "Cache made us hand back a different result?");
+#endif
+  if (AutoResetWalker)
+    resetClobberWalker();
+  return New;
+}
+
+MemoryAccess *MemorySSA::CachingWalker::getClobberingMemoryAccess(
+    MemoryAccess *StartingAccess, const MemoryLocation &Loc) {
+  if (isa<MemoryPhi>(StartingAccess))
+    return StartingAccess;
+
+  auto *StartingUseOrDef = cast<MemoryUseOrDef>(StartingAccess);
+  if (MSSA->isLiveOnEntryDef(StartingUseOrDef))
+    return StartingUseOrDef;
+
+  Instruction *I = StartingUseOrDef->getMemoryInst();
+
+  // Conservatively, fences are always clobbers, so don't perform the walk if we
+  // hit a fence.
+  if (!ImmutableCallSite(I) && I->isFenceLike())
+    return StartingUseOrDef;
+
+  UpwardsMemoryQuery Q;
+  Q.OriginalAccess = StartingUseOrDef;
+  Q.StartingLoc = Loc;
+  Q.Inst = I;
+  Q.IsCall = false;
+
+  // Unlike the other function, do not walk to the def of a def, because we are
+  // handed something we already believe is the clobbering access.
+  MemoryAccess *DefiningAccess = isa<MemoryUse>(StartingUseOrDef)
+                                     ? StartingUseOrDef->getDefiningAccess()
+                                     : StartingUseOrDef;
+
+  MemoryAccess *Clobber = getClobberingMemoryAccess(DefiningAccess, Q);
+  DEBUG(dbgs() << "Starting Memory SSA clobber for " << *I << " is ");
+  DEBUG(dbgs() << *StartingUseOrDef << "\n");
+  DEBUG(dbgs() << "Final Memory SSA clobber for " << *I << " is ");
+  DEBUG(dbgs() << *Clobber << "\n");
+  return Clobber;
+}
+
+MemoryAccess *
+MemorySSA::CachingWalker::getClobberingMemoryAccess(MemoryAccess *MA) {
+  auto *StartingAccess = dyn_cast<MemoryUseOrDef>(MA);
+  // If this is a MemoryPhi, we can't do anything.
+  if (!StartingAccess)
+    return MA;
+
+  // If this is an already optimized use or def, return the optimized result.
+  // Note: Currently, we do not store the optimized def result because we'd need
+  // a separate field, since we can't use it as the defining access.
+  if (auto *MUD = dyn_cast<MemoryUseOrDef>(StartingAccess))
+    if (MUD->isOptimized())
+      return MUD->getOptimized();
+
+  const Instruction *I = StartingAccess->getMemoryInst();
+  UpwardsMemoryQuery Q(I, StartingAccess);
+  // We can't sanely do anything with a fences, they conservatively
+  // clobber all memory, and have no locations to get pointers from to
+  // try to disambiguate.
+  if (!Q.IsCall && I->isFenceLike())
+    return StartingAccess;
+
+  if (isUseTriviallyOptimizableToLiveOnEntry(*MSSA->AA, I)) {
+    MemoryAccess *LiveOnEntry = MSSA->getLiveOnEntryDef();
+    if (auto *MUD = dyn_cast<MemoryUseOrDef>(StartingAccess))
+      MUD->setOptimized(LiveOnEntry);
+    return LiveOnEntry;
+  }
+
+  // Start with the thing we already think clobbers this location
+  MemoryAccess *DefiningAccess = StartingAccess->getDefiningAccess();
+
+  // At this point, DefiningAccess may be the live on entry def.
+  // If it is, we will not get a better result.
+  if (MSSA->isLiveOnEntryDef(DefiningAccess))
+    return DefiningAccess;
+
+  MemoryAccess *Result = getClobberingMemoryAccess(DefiningAccess, Q);
+  DEBUG(dbgs() << "Starting Memory SSA clobber for " << *I << " is ");
+  DEBUG(dbgs() << *DefiningAccess << "\n");
+  DEBUG(dbgs() << "Final Memory SSA clobber for " << *I << " is ");
+  DEBUG(dbgs() << *Result << "\n");
+  if (auto *MUD = dyn_cast<MemoryUseOrDef>(StartingAccess))
+    MUD->setOptimized(Result);
+
+  return Result;
+}
+
+MemoryAccess *
+DoNothingMemorySSAWalker::getClobberingMemoryAccess(MemoryAccess *MA) {
+  if (auto *Use = dyn_cast<MemoryUseOrDef>(MA))
+    return Use->getDefiningAccess();
+  return MA;
+}
+
+MemoryAccess *DoNothingMemorySSAWalker::getClobberingMemoryAccess(
+    MemoryAccess *StartingAccess, const MemoryLocation &) {
+  if (auto *Use = dyn_cast<MemoryUseOrDef>(StartingAccess))
+    return Use->getDefiningAccess();
+  return StartingAccess;
+}
+} // namespace llvm