Index: include/llvm/Analysis/LoopAnalysisManager.h
===================================================================
--- include/llvm/Analysis/LoopAnalysisManager.h
+++ include/llvm/Analysis/LoopAnalysisManager.h
@@ -37,6 +37,7 @@
 #include "llvm/Analysis/BasicAliasAnalysis.h"
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/MemorySSA.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
@@ -58,6 +59,7 @@
   ScalarEvolution &SE;
   TargetLibraryInfo &TLI;
   TargetTransformInfo &TTI;
+  MemorySSA &MSSA;
 };
 
 /// Extern template declaration for the analysis set for this IR unit.
Index: include/llvm/Support/Debug.h
===================================================================
--- include/llvm/Support/Debug.h
+++ include/llvm/Support/Debug.h
@@ -93,6 +93,14 @@
 ///
 extern bool VerifyLoopInfo;
 
+/// Enables memory ssa as a dependency for loop passes.
+///
+extern bool EnableMSSALoopDep;
+
+/// Enables LICM to use MSSA if available
+///
+extern bool UseLICMwMSSA;
+
 ///\}
 
 /// EnableDebugBuffering - This defaults to false.  If true, the debug
Index: include/llvm/Transforms/Scalar/LoopPassManager.h
===================================================================
--- include/llvm/Transforms/Scalar/LoopPassManager.h
+++ include/llvm/Transforms/Scalar/LoopPassManager.h
@@ -271,13 +271,15 @@
       return PA;
 
     // Get the analysis results needed by loop passes.
-    LoopStandardAnalysisResults LAR = {AM.getResult<AAManager>(F),
-                                       AM.getResult<AssumptionAnalysis>(F),
-                                       AM.getResult<DominatorTreeAnalysis>(F),
-                                       AM.getResult<LoopAnalysis>(F),
-                                       AM.getResult<ScalarEvolutionAnalysis>(F),
-                                       AM.getResult<TargetLibraryAnalysis>(F),
-                                       AM.getResult<TargetIRAnalysis>(F)};
+    LoopStandardAnalysisResults LAR = {
+        AM.getResult<AAManager>(F),
+        AM.getResult<AssumptionAnalysis>(F),
+        AM.getResult<DominatorTreeAnalysis>(F),
+        AM.getResult<LoopAnalysis>(F),
+        AM.getResult<ScalarEvolutionAnalysis>(F),
+        AM.getResult<TargetLibraryAnalysis>(F),
+        AM.getResult<TargetIRAnalysis>(F),
+        AM.getResult<MemorySSAAnalysis>(F).getMSSA()};
 
     // Setup the loop analysis manager from its proxy. It is important that
     // this is only done when there are loops to process and we have built the
@@ -345,6 +347,9 @@
     PA.preserve<DominatorTreeAnalysis>();
     PA.preserve<LoopAnalysis>();
     PA.preserve<ScalarEvolutionAnalysis>();
+    if (EnableMSSALoopDep) {
+      PA.preserve<MemorySSAAnalysis>();
+    }
     // FIXME: What we really want to do here is preserve an AA category, but
     // that concept doesn't exist yet.
     PA.preserve<AAManager>();
Index: include/llvm/Transforms/Utils/LoopUtils.h
===================================================================
--- include/llvm/Transforms/Utils/LoopUtils.h
+++ include/llvm/Transforms/Utils/LoopUtils.h
@@ -38,6 +38,9 @@
 class DataLayout;
 class Loop;
 class LoopInfo;
+class MemorySSA;
+class MemorySSAUpdater;
+class MemorySSAAliasSets;
 class OptimizationRemarkEmitter;
 class PredicatedScalarEvolution;
 class PredIteratorCache;
@@ -425,7 +428,8 @@
 /// arguments. Diagnostics is emitted via \p ORE. It returns changed status.
 bool sinkRegion(DomTreeNode *, AliasAnalysis *, LoopInfo *, DominatorTree *,
                 TargetLibraryInfo *, Loop *, AliasSetTracker *,
-                LoopSafetyInfo *, OptimizationRemarkEmitter *ORE);
+                MemorySSAUpdater *, MemorySSA *, LoopSafetyInfo *,
+                OptimizationRemarkEmitter *ORE);
 
 /// \brief Walk the specified region of the CFG (defined by all blocks
 /// dominated by the specified block, and that are in the current loop) in depth
@@ -437,7 +441,8 @@
 /// ORE. It returns changed status.
 bool hoistRegion(DomTreeNode *, AliasAnalysis *, LoopInfo *, DominatorTree *,
                  TargetLibraryInfo *, Loop *, AliasSetTracker *,
-                 LoopSafetyInfo *, OptimizationRemarkEmitter *ORE);
+                 MemorySSAUpdater *, MemorySSA *, LoopSafetyInfo *,
+                 OptimizationRemarkEmitter *ORE);
 
 /// \brief Try to promote memory values to scalars by sinking stores out of
 /// the loop and moving loads to before the loop.  We do this by looping over
@@ -446,19 +451,18 @@
 /// vector, loop exit blocks insertion point vector, PredIteratorCache,
 /// LoopInfo, DominatorTree, Loop, AliasSet information for all instructions
 /// of the loop and loop safety information as arguments.
+/// The AliasSetTracker and MemorySSAAliasSets are alternatives to one another.
 /// Diagnostics is emitted via \p ORE. It returns changed status.
-bool promoteLoopAccessesToScalars(const SmallSetVector<Value *, 8> &,
-                                  SmallVectorImpl<BasicBlock *> &,
-                                  SmallVectorImpl<Instruction *> &,
-                                  PredIteratorCache &, LoopInfo *,
-                                  DominatorTree *, const TargetLibraryInfo *,
-                                  Loop *, AliasSetTracker *, LoopSafetyInfo *,
-                                  OptimizationRemarkEmitter *);
+bool promoteLoopAccessesToScalars(
+    const SmallSetVector<Value *, 8> &, SmallVectorImpl<BasicBlock *> &,
+    SmallVectorImpl<Instruction *> &, PredIteratorCache &, LoopInfo *,
+    DominatorTree *, const TargetLibraryInfo *, Loop *, AliasSetTracker *,
+    MemorySSAAliasSets *, LoopSafetyInfo *, OptimizationRemarkEmitter *);
 
 /// Does a BFS from a given node to all of its children inside a given loop.
 /// The returned vector of nodes includes the starting point.
 SmallVector<DomTreeNode *, 16> collectChildrenInLoop(DomTreeNode *N,
-                                                     const Loop *CurLoop);
+                                                     Loop *CurLoop);
 
 /// \brief Computes safety information for a loop
 /// checks loop body & header for the possibility of may throw
@@ -506,9 +510,9 @@
 /// instructions from loop body to preheader/exit. Check if the instruction
 /// can execute speculatively.
 /// If \p ORE is set use it to emit optimization remarks.
-bool canSinkOrHoistInst(Instruction &I, AAResults *AA, DominatorTree *DT,
-                        Loop *CurLoop, AliasSetTracker *CurAST,
-                        LoopSafetyInfo *SafetyInfo,
+bool canSinkOrHoistInst(Instruction &, AAResults *, DominatorTree *, Loop *,
+                        AliasSetTracker *, MemorySSAUpdater *, MemorySSA *,
+                        LoopSafetyInfo *,
                         OptimizationRemarkEmitter *ORE = nullptr);
 
 /// Generates a vector reduction using shufflevectors to reduce the value.
Index: include/llvm/Transforms/Utils/MemorySSAAliasSets.h
===================================================================
--- /dev/null
+++ include/llvm/Transforms/Utils/MemorySSAAliasSets.h
@@ -0,0 +1,303 @@
+//===-- MemorySSAAliasSets.h - Alias sets using MemorySSA -----------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// This a a helper class that creates alias sets using MemorySSA, each
+// set being marked with properties that enablei/disable promotion.
+// It is used for promotion in the Loop Invariant Code Motion Pass.
+// It also stores insertion points into MemorySSA for a particular loop.
+// These need to be reset if the sets are reused.
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_ANALYSIS_MEMORYSSA_ALIASSETS_H
+#define LLVM_ANALYSIS_MEMORYSSA_ALIASSETS_H
+
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/BasicAliasAnalysis.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/MemorySSA.h"
+#include "llvm/Analysis/MemorySSAUpdater.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
+
+using namespace llvm;
+
+namespace llvm {
+class MemorySSAAliasSets {
+public:
+  MemorySSA *MSSA;
+  MemorySSAUpdater *MSSAUpdater;
+
+private:
+  Loop *L;
+  LoopInfo *LI;
+  AliasAnalysis *AA;
+  DominatorTree *DT;
+  SmallVector<MemoryAccess *, 4> MSSAInsertPts;
+
+  class SingleMustAliasVec {
+    MemoryLocation Loc;
+    SmallSetVector<Value *, 8> Vec;
+
+  public:
+    // CanNeverPromote trumps everything else
+    // Set is either may-alias, has a volatile store or aliases an instruction
+    // witout a MemoryLocation.
+    bool CanNeverPromote = false;
+    bool LoopInvariantAccess = false;
+    bool HasAGoodStore = false;
+    SingleMustAliasVec(MemoryLocation loc) : Loc(loc), CanNeverPromote(false) {
+      Vec.insert(const_cast<Value *>(Loc.Ptr));
+    }
+    void addMemoryLocation(Optional<MemoryLocation> MemLoc) {
+      if (MemLoc == None)
+        return;
+      Vec.insert(const_cast<Value *>(MemLoc.getValue().Ptr));
+    }
+    MemoryLocation getMemoryLocation() { return Loc; }
+    SmallSetVector<Value *, 8> *getVecRef() { return &Vec; }
+    bool isGoodForPromotion() {
+      return !CanNeverPromote && LoopInvariantAccess && HasAGoodStore;
+    }
+    void setMemoryLocation(Value *LI, Value *Replacement) {
+      Loc = MemoryLocation(Replacement, Loc.Size, Loc.AATags);
+      Vec.remove(LI);
+      Vec.insert(Replacement);
+    }
+    void dump() {
+      dbgs() << "Set cannot be promoted: " << CanNeverPromote << "\n";
+      dbgs() << "Has only loop invariant accesses: " << LoopInvariantAccess
+             << "\n";
+      dbgs() << "Contains a promotable store: " << HasAGoodStore << "\n";
+      dbgs() << "Contents: \n";
+      for (Value *V : Vec)
+        dbgs() << " Value: " << *V << "\n";
+    }
+  };
+
+  SmallVector<SingleMustAliasVec *, 4> AllSets;
+  DenseMap<const MemoryAccess *, SingleMustAliasVec *> StoredDefs;
+  unsigned MemorySSATraversalPenalty = 0;
+  unsigned CAP_NO_ALIAS_SETS = 30;
+  unsigned CAP_MSSA_TRAVERSALS = 30;
+
+  void dump() {
+    for (SingleMustAliasVec *Set : AllSets)
+      Set->dump();
+  }
+
+  bool isLoopInvariant(const Value *V) {
+    if(!L)
+      return true;
+    return L->isLoopInvariant(V);
+  }
+  bool loopContains(Instruction *I) {
+    if(!L)
+      return true;
+    return L->contains(I);
+  }
+  bool loopContains(BasicBlock *B) {
+    if(!L)
+      return true;
+    return L->contains(B);
+  }
+
+  AliasResult alias(Optional<MemoryLocation> MemLocI, Instruction *InstrI,
+                    MemoryLocation &MemLocJ) {
+    if (MemLocI == None) {
+      ModRefInfo ModRef = AA->getModRefInfo(InstrI, MemLocJ);
+      if (bool(ModRef & MRI_Mod)) {
+        return MustAlias;
+      }
+      if (bool(ModRef & MRI_Ref)) {
+        return MayAlias;
+      }
+      return NoAlias;
+    } else {
+      AliasResult Result = AA->alias(MemLocI.getValue(), MemLocJ);
+      return Result;
+    }
+  }
+
+  void addToAliasSets(const MemoryUse *Use) {
+    // Follow-up to the BIG NOTE:
+    // Because we allowed some imprecision, it is possible that the
+    // definingAccess is not the clobberingAccess. We *really* want the
+    // correct aliasing definition here, otherwise we're creating a set with
+    // things that don't alias.
+    // This is currently visible in "LoopSimplify/ashr-crash.ll"(Puts @a,@c,@d
+    // in the same set because its uses all point to the newly promoted Def)
+    // We *have to* use getClobberingAccess here for correctness!
+    // To avoid incurring the performance penalty of complete info:
+    // - we don't check against existing sets
+    // - we get first defining access, then clobbering access. If the two are
+    // different, then we increment a local cost - the cost of optimizing the
+    // info for this use past the "memssa-check-limit".
+    // - we stop creating sets after CAP_MSSA_TRAVERSALS calls to getClobbering
+    // that did work (result != getDefining).
+    // - we do *not* have partial info to reuse, so nothing is promoted when
+    // cost is exceeded.
+    MemoryDef *DefiningAcc = dyn_cast_or_null<MemoryDef>(
+        const_cast<MemoryUse *>(Use)->getDefiningAccess());
+    MemoryDef *ClobberingAcc = dyn_cast_or_null<MemoryDef>(
+        MSSA->getWalker()->getClobberingMemoryAccess(
+            const_cast<MemoryUse *>(Use)));
+
+    if (DefiningAcc != ClobberingAcc)
+      MemorySSATraversalPenalty++;
+    if (!ClobberingAcc || !ClobberingAcc->getMemoryInst())
+      return;
+
+    SingleMustAliasVec *OneAliasSet = StoredDefs[ClobberingAcc];
+    if (!OneAliasSet)
+      return;
+
+    Instruction *InstrI = Use->getMemoryInst();
+    Optional<MemoryLocation> MemLocI = MemoryLocation::getOrNone(InstrI);
+    MemoryLocation MemLocJ = OneAliasSet->getMemoryLocation();
+    // FIXME: This is KNOWN by MSSA, i.e. if may or must. TODO: expose this.
+    AliasResult Result = alias(MemLocI, InstrI, MemLocJ);
+    if (Result == MayAlias) {
+      OneAliasSet->CanNeverPromote = true;
+    }
+    OneAliasSet->addMemoryLocation(MemLocI);
+  }
+
+  void addToAliasSets(const MemoryDef *Def) {
+    Instruction *InstrI = Def->getMemoryInst();
+    Optional<MemoryLocation> MemLocI = MemoryLocation::getOrNone(InstrI);
+
+    SingleMustAliasVec *FoundMustAlias = nullptr;
+    bool FoundMayAlias = false;
+
+    StoreInst *SIn = dyn_cast_or_null<StoreInst>(InstrI);
+    bool LoopInvariantAccess =
+        ((MemLocI != None) && isLoopInvariant(MemLocI.getValue().Ptr));
+    bool CanNeverPromote = (SIn && SIn->isVolatile()) || MemLocI == None;
+    bool HasAGoodStore = SIn && !SIn->isVolatile();
+
+    for (auto OneAliasSet : AllSets) {
+      MemoryLocation MemLocJ = OneAliasSet->getMemoryLocation();
+      AliasResult Result = alias(MemLocI, InstrI, MemLocJ);
+      if (Result == MustAlias) {
+        OneAliasSet->addMemoryLocation(MemLocI);
+        if (FoundMustAlias != nullptr || CanNeverPromote) {
+          OneAliasSet->CanNeverPromote = true;
+          FoundMayAlias = true;
+          if (FoundMustAlias) {
+            FoundMustAlias->CanNeverPromote = true;
+          }
+        }
+        OneAliasSet->LoopInvariantAccess |= LoopInvariantAccess;
+        OneAliasSet->HasAGoodStore |= HasAGoodStore;
+        FoundMustAlias = OneAliasSet;
+        StoredDefs[Def] = FoundMustAlias;
+      }
+      if (Result == MayAlias) {
+        FoundMayAlias = true;
+        OneAliasSet->CanNeverPromote = true;
+        if (FoundMustAlias) {
+          FoundMustAlias->CanNeverPromote = true;
+        }
+      }
+    }
+
+    // Still need to add this to a new set
+    if (!FoundMustAlias && MemLocI != None) {
+      SingleMustAliasVec *newEntry = new SingleMustAliasVec(MemLocI.getValue());
+      newEntry->CanNeverPromote = CanNeverPromote || FoundMayAlias;
+      newEntry->LoopInvariantAccess = LoopInvariantAccess;
+      newEntry->HasAGoodStore = HasAGoodStore;
+      StoredDefs[Def] = newEntry;
+      AllSets.push_back(newEntry);
+    }
+  }
+
+public:
+  MemorySSAAliasSets(MemorySSA *mssa, MemorySSAUpdater *mssaupdater, Loop *l,
+                     LoopInfo *li, AliasAnalysis *aa, DominatorTree *dt,
+                     SmallVectorImpl<BasicBlock *> &ExitBlocks)
+      : MSSA(mssa), MSSAUpdater(mssaupdater), L(l), LI(li), AA(aa), DT(dt),
+        AllSets() {
+    resetMSSAInsertPts(ExitBlocks);
+  }
+
+  void resetMSSAInsertPts(SmallVectorImpl<BasicBlock *> &ExitBlocks) {
+    // TODO: Better way to fill this in.
+    MSSAInsertPts.reserve(ExitBlocks.size());
+    for (unsigned I = 0; I < ExitBlocks.size(); ++I) {
+      MSSAInsertPts.push_back(nullptr);
+    }
+  }
+
+  // Creates all alias sets in L
+  void createSets() { addToSets(DT->getNode(L->getHeader())); }
+
+  // Create all alias sets given a basic block (for testing)
+  void createSets(BasicBlock *B) { addToSets(DT->getNode(B)); }
+
+  void addToSets(DomTreeNode *N) {
+    // We want to visit parents before children. We will enque all the parents
+    // before their children in the worklist and process the worklist in order.
+    SmallVector<DomTreeNode *, 16> Worklist = collectChildrenInLoop(N, L);
+
+    for (DomTreeNode *DTN : Worklist) {
+      BasicBlock *BB = DTN->getBlock();
+      auto *Accesses = MSSA->getBlockAccesses(BB);
+      if (Accesses)
+        for (auto &Acc : make_range(Accesses->begin(), Accesses->end())) {
+          if (AllSets.size() > CAP_NO_ALIAS_SETS ||
+              MemorySSATraversalPenalty > CAP_MSSA_TRAVERSALS) {
+            AllSets.clear();
+            return;
+          }
+          // Process uses
+          const MemoryUse *Use = dyn_cast_or_null<MemoryUse>(&Acc);
+          if (Use)
+            addToAliasSets(Use);
+          // Process defs
+          const MemoryDef *Def = dyn_cast_or_null<MemoryDef>(&Acc);
+          if (Def)
+            addToAliasSets(Def);
+        }
+    }
+    // dbgs()<<"No sets: "<<AllSets.size()<<" and mssa penalty:
+    // "<<MemorySSATraversalPenalty<<"\n";  dump();
+  }
+
+  SmallSetVector<Value *, 8> *getSetIfPromotableOrNull(unsigned I) {
+    if (AllSets[I]->isGoodForPromotion()) {
+      SmallSetVector<Value *, 8> *MustAliasPtrs = AllSets[I]->getVecRef();
+      assert(MustAliasPtrs->size() > 0 && "Alias set cannot be empty!!!\n");
+      return MustAliasPtrs;
+    }
+    return nullptr;
+  }
+
+  unsigned size() { return AllSets.size(); }
+
+  void replace(Value *LoadI, Value *Replacement) {
+    for (auto OneAliasSet : AllSets) {
+      MemoryLocation MemLocJ = OneAliasSet->getMemoryLocation();
+      if (MemLocJ.Ptr == LoadI) {
+        OneAliasSet->setMemoryLocation(LoadI, Replacement);
+        if (!OneAliasSet->CanNeverPromote && OneAliasSet->HasAGoodStore &&
+            !OneAliasSet->LoopInvariantAccess &&
+            isLoopInvariant(Replacement)) {
+          OneAliasSet->LoopInvariantAccess = true;
+        }
+      }
+    }
+  }
+
+  MemoryAccess *getInsertPoint(int I) { return MSSAInsertPts[I]; }
+  void setInsertPoint(MemoryAccess *Acc, int I) { MSSAInsertPts[I] = Acc; }
+};
+} // end namespace llvm
+
+#endif // LLVM_ANALYSIS_MEMORYSSA_ALIASSETS_H
Index: lib/Analysis/LoopAnalysisManager.cpp
===================================================================
--- lib/Analysis/LoopAnalysisManager.cpp
+++ lib/Analysis/LoopAnalysisManager.cpp
@@ -11,6 +11,7 @@
 #include "llvm/Analysis/BasicAliasAnalysis.h"
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/MemorySSA.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
 #include "llvm/IR/Dominators.h"
@@ -45,12 +46,22 @@
   // loop analyses declare any dependencies on these and use the more general
   // invalidation logic below to act on that.
   auto PAC = PA.getChecker<LoopAnalysisManagerFunctionProxy>();
+  bool invalidateMemorySSAAnalysis = false;
+  // Only invalidate MSSA when used in LICM. Caveat: Building MSSA for nothing!
+  // The alternative: always invalidate MemorySSA, until all loop passes preserve it
+  // This alternative change will need to fix:
+  //    unittests/Scalar/ScalarTests/LoopPassManagerTest,
+  //    test/Transforms/LoopUnroll/unroll-loop-invalidation.ll and
+  //    test/Other/loop-pm-invalidation.ll
+  if (UseLICMwMSSA && !EnableMSSALoopDep)
+    invalidateMemorySSAAnalysis = Inv.invalidate<MemorySSAAnalysis>(F, PA);
   if (!(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>()) ||
       Inv.invalidate<AAManager>(F, PA) ||
       Inv.invalidate<AssumptionAnalysis>(F, PA) ||
       Inv.invalidate<DominatorTreeAnalysis>(F, PA) ||
       Inv.invalidate<LoopAnalysis>(F, PA) ||
-      Inv.invalidate<ScalarEvolutionAnalysis>(F, PA)) {
+      Inv.invalidate<ScalarEvolutionAnalysis>(F, PA) ||
+      invalidateMemorySSAAnalysis) {
     // Note that the LoopInfo may be stale at this point, however the loop
     // objects themselves remain the only viable keys that could be in the
     // analysis manager's cache. So we just walk the keys and forcibly clear
@@ -135,6 +146,9 @@
   PA.preserve<LoopAnalysis>();
   PA.preserve<LoopAnalysisManagerFunctionProxy>();
   PA.preserve<ScalarEvolutionAnalysis>();
+  if (EnableMSSALoopDep) {
+    PA.preserve<MemorySSAAnalysis>();
+  }
   // TODO: What we really want to do here is preserve an AA category, but that
   // concept doesn't exist yet.
   PA.preserve<AAManager>();
Index: lib/Analysis/MemorySSA.cpp
===================================================================
--- lib/Analysis/MemorySSA.cpp
+++ lib/Analysis/MemorySSA.cpp
@@ -55,6 +55,8 @@
 #include <utility>
 
 using namespace llvm;
+bool llvm::EnableMSSALoopDep = false;
+bool llvm::UseLICMwMSSA = false;
 
 #define DEBUG_TYPE "memoryssa"
 
Index: lib/Transforms/Scalar/LICM.cpp
===================================================================
--- lib/Transforms/Scalar/LICM.cpp
+++ lib/Transforms/Scalar/LICM.cpp
@@ -42,6 +42,8 @@
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/LoopPass.h"
 #include "llvm/Analysis/MemoryBuiltins.h"
+#include "llvm/Analysis/MemorySSA.h"
+#include "llvm/Analysis/MemorySSAUpdater.h"
 #include "llvm/Analysis/OptimizationDiagnosticInfo.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
@@ -64,6 +66,7 @@
 #include "llvm/Transforms/Scalar/LoopPassManager.h"
 #include "llvm/Transforms/Utils/Local.h"
 #include "llvm/Transforms/Utils/LoopUtils.h"
+#include "llvm/Transforms/Utils/MemorySSAAliasSets.h"
 #include "llvm/Transforms/Utils/SSAUpdater.h"
 #include <algorithm>
 #include <utility>
@@ -91,10 +94,12 @@
 static bool isNotUsedInLoop(const Instruction &I, const Loop *CurLoop,
                             const LoopSafetyInfo *SafetyInfo);
 static bool hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
+                  MemorySSAUpdater *MSSAUpdater, MemorySSA *MSSA,
                   const LoopSafetyInfo *SafetyInfo,
                   OptimizationRemarkEmitter *ORE);
 static bool sink(Instruction &I, const LoopInfo *LI, const DominatorTree *DT,
                  const Loop *CurLoop, AliasSetTracker *CurAST,
+                 MemorySSAUpdater *MSSAUpdater, MemorySSA *MSSA,
                  const LoopSafetyInfo *SafetyInfo,
                  OptimizationRemarkEmitter *ORE);
 static bool isSafeToExecuteUnconditionally(Instruction &Inst,
@@ -106,15 +111,21 @@
 static bool pointerInvalidatedByLoop(Value *V, uint64_t Size,
                                      const AAMDNodes &AAInfo,
                                      AliasSetTracker *CurAST);
+static bool pointerInvalidatedByLoopWithMSSA(Value *V, MemorySSA *MSSA,
+                                             MemoryUseOrDef *MUD,
+                                             Loop *CurLoop);
+static void removeFromMSSA(Instruction *I, MemorySSAUpdater *MSSAUpdater,
+                           MemorySSA *MSSA);
 static Instruction *
 CloneInstructionInExitBlock(Instruction &I, BasicBlock &ExitBlock, PHINode &PN,
+                            MemorySSAUpdater *MSSAUpdater, MemorySSA *MSSA,
                             const LoopInfo *LI,
                             const LoopSafetyInfo *SafetyInfo);
 
 namespace {
 struct LoopInvariantCodeMotion {
   bool runOnLoop(Loop *L, AliasAnalysis *AA, LoopInfo *LI, DominatorTree *DT,
-                 TargetLibraryInfo *TLI, ScalarEvolution *SE,
+                 TargetLibraryInfo *TLI, ScalarEvolution *SE, MemorySSA *MSSA,
                  OptimizationRemarkEmitter *ORE, bool DeleteAST);
 
   DenseMap<Loop *, AliasSetTracker *> &getLoopToAliasSetMap() {
@@ -126,6 +137,7 @@
 
   AliasSetTracker *collectAliasInfoForLoop(Loop *L, LoopInfo *LI,
                                            AliasAnalysis *AA);
+  MemorySSAUpdater *MSSAUpdater = nullptr;
 };
 
 struct LegacyLICMPass : public LoopPass {
@@ -150,12 +162,13 @@
     // pass.  Function analyses need to be preserved across loop transformations
     // but ORE cannot be preserved (see comment before the pass definition).
     OptimizationRemarkEmitter ORE(L->getHeader()->getParent());
-    return LICM.runOnLoop(L,
-                          &getAnalysis<AAResultsWrapperPass>().getAAResults(),
-                          &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(),
-                          &getAnalysis<DominatorTreeWrapperPass>().getDomTree(),
-                          &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(),
-                          SE ? &SE->getSE() : nullptr, &ORE, false);
+    return LICM.runOnLoop(
+        L, &getAnalysis<AAResultsWrapperPass>().getAAResults(),
+        &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(),
+        &getAnalysis<DominatorTreeWrapperPass>().getDomTree(),
+        &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(),
+        SE ? &SE->getSE() : nullptr,
+        &getAnalysis<MemorySSAWrapperPass>().getMSSA(), &ORE, false);
   }
 
   /// This transformation requires natural loop information & requires that
@@ -164,6 +177,7 @@
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.setPreservesCFG();
     AU.addRequired<TargetLibraryInfoWrapperPass>();
+    AU.addRequired<MemorySSAWrapperPass>();
     getLoopAnalysisUsage(AU);
   }
 
@@ -204,7 +218,9 @@
                        "cached at a higher level");
 
   LoopInvariantCodeMotion LICM;
-  if (!LICM.runOnLoop(&L, &AR.AA, &AR.LI, &AR.DT, &AR.TLI, &AR.SE, ORE, true))
+  MemorySSA *MSSA = UseLICMwMSSA ? (&AR.MSSA) : nullptr;
+  if (!LICM.runOnLoop(&L, &AR.AA, &AR.LI, &AR.DT, &AR.TLI, &AR.SE, MSSA, ORE,
+                      true))
     return PreservedAnalyses::all();
 
   auto PA = getLoopPassPreservedAnalyses();
@@ -217,6 +233,7 @@
                       false, false)
 INITIALIZE_PASS_DEPENDENCY(LoopPass)
 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
 INITIALIZE_PASS_END(LegacyLICMPass, "licm", "Loop Invariant Code Motion", false,
                     false)
 
@@ -231,14 +248,24 @@
 bool LoopInvariantCodeMotion::runOnLoop(Loop *L, AliasAnalysis *AA,
                                         LoopInfo *LI, DominatorTree *DT,
                                         TargetLibraryInfo *TLI,
-                                        ScalarEvolution *SE,
+                                        ScalarEvolution *SE, MemorySSA *MSSA,
                                         OptimizationRemarkEmitter *ORE,
                                         bool DeleteAST) {
   bool Changed = false;
 
   assert(L->isLCSSAForm(*DT) && "Loop is not in LCSSA form.");
 
-  AliasSetTracker *CurAST = collectAliasInfoForLoop(L, LI, AA);
+  AliasSetTracker *CurAST = nullptr;
+  if (!MSSA) {
+    // Note: MSSA disabled in the new PM until all loop passes preserve MSSA
+    DEBUG(dbgs() << "LICM: Using Alias Set Tracker\n");
+    CurAST = collectAliasInfoForLoop(L, LI, AA);
+    MSSAUpdater = nullptr;
+  } else {
+    DEBUG(dbgs() << "LICM: Using MemorySSA\n");
+    CurAST = nullptr;
+    MSSAUpdater = new MemorySSAUpdater(MSSA);
+  }
 
   // Get the preheader block to move instructions into...
   BasicBlock *Preheader = L->getLoopPreheader();
@@ -259,10 +286,11 @@
   //
   if (L->hasDedicatedExits())
     Changed |= sinkRegion(DT->getNode(L->getHeader()), AA, LI, DT, TLI, L,
-                          CurAST, &SafetyInfo, ORE);
+                          CurAST, MSSAUpdater, MSSA, &SafetyInfo, ORE);
+
   if (Preheader)
     Changed |= hoistRegion(DT->getNode(L->getHeader()), AA, LI, DT, TLI, L,
-                           CurAST, &SafetyInfo, ORE);
+                           CurAST, MSSAUpdater, MSSA, &SafetyInfo, ORE);
 
   // Now that all loop invariants have been removed from the loop, promote any
   // memory references to scalars that we can.
@@ -291,26 +319,41 @@
 
       bool Promoted = false;
 
-      // Loop over all of the alias sets in the tracker object.
-      for (AliasSet &AS : *CurAST) {
-        // We can promote this alias set if it has a store, if it is a "Must"
-        // alias set, if the pointer is loop invariant, and if we are not
-        // eliminating any volatile loads or stores.
-        if (AS.isForwardingAliasSet() || !AS.isMod() || !AS.isMustAlias() ||
-            AS.isVolatile() || !L->isLoopInvariant(AS.begin()->getValue()))
-          continue;
-
-        assert(
-            !AS.empty() &&
-            "Must alias set should have at least one pointer element in it!");
-
-        SmallSetVector<Value *, 8> PointerMustAliases;
-        for (const auto &ASI : AS)
-          PointerMustAliases.insert(ASI.getValue());
-
-        Promoted |= promoteLoopAccessesToScalars(PointerMustAliases, ExitBlocks,
-                                                 InsertPts, PIC, LI, DT, TLI, L,
-                                                 CurAST, &SafetyInfo, ORE);
+      if (CurAST) {
+        // Loop over all of the alias sets in the tracker object.
+        for (AliasSet &AS : *CurAST) {
+          // We can promote this alias set if it has a store, if it is a "Must"
+          // alias set, if the pointer is loop invariant, and if we are not
+          // eliminating any volatile loads or stores.
+          if (AS.isForwardingAliasSet() || !AS.isMod() || !AS.isMustAlias() ||
+              AS.isVolatile() || !L->isLoopInvariant(AS.begin()->getValue()))
+            continue;
+
+          assert(
+              !AS.empty() &&
+              "Must alias set should have at least one pointer element in it!");
+
+          SmallSetVector<Value *, 8> PointerMustAliases;
+          for (const auto &ASI : AS)
+            PointerMustAliases.insert(ASI.getValue());
+
+          Promoted |= promoteLoopAccessesToScalars(
+              PointerMustAliases, ExitBlocks, InsertPts, PIC, LI, DT, TLI, L,
+              CurAST, nullptr, &SafetyInfo, ORE);
+        }
+      } else {
+        MemorySSAAliasSets AS(MSSA, MSSAUpdater, L, LI, AA, DT, ExitBlocks);
+        AS.createSets();
+
+        for (unsigned I = 0; I < AS.size(); ++I) {
+          SmallSetVector<Value *, 8> *MustAliasPtrs =
+              AS.getSetIfPromotableOrNull(I);
+          if (MustAliasPtrs) {
+            Promoted |= promoteLoopAccessesToScalars(
+                *MustAliasPtrs, ExitBlocks, InsertPts, PIC, LI, DT, TLI, L,
+                CurAST, &AS, &SafetyInfo, ORE);
+          }
+        }
       }
 
       // Once we have promoted values across the loop body we have to
@@ -333,12 +376,15 @@
   assert((!L->getParentLoop() || L->getParentLoop()->isLCSSAForm(*DT)) &&
          "Parent loop not left in LCSSA form after LICM!");
 
-  // If this loop is nested inside of another one, save the alias information
-  // for when we process the outer loop.
-  if (L->getParentLoop() && !DeleteAST)
-    LoopToAliasSetMap[L] = CurAST;
-  else
-    delete CurAST;
+  if (CurAST) {
+    // If this loop is nested inside of another one, save the alias information
+    // for when we process the outer loop.
+    if (L->getParentLoop() && !DeleteAST)
+      LoopToAliasSetMap[L] = CurAST;
+    else
+      delete CurAST;
+  } else
+    delete MSSAUpdater;
 
   if (Changed && SE)
     SE->forgetLoopDispositions(L);
@@ -352,12 +398,15 @@
 ///
 bool llvm::sinkRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
                       DominatorTree *DT, TargetLibraryInfo *TLI, Loop *CurLoop,
-                      AliasSetTracker *CurAST, LoopSafetyInfo *SafetyInfo,
+                      AliasSetTracker *CurAST, MemorySSAUpdater *MSSAUpdater,
+                      MemorySSA *MSSA, LoopSafetyInfo *SafetyInfo,
                       OptimizationRemarkEmitter *ORE) {
 
   // Verify inputs.
   assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr &&
-         CurLoop != nullptr && CurAST != nullptr && SafetyInfo != nullptr &&
+         CurLoop != nullptr && SafetyInfo != nullptr &&
+         "Unexpected input to sinkRegion");
+  assert((CurAST != nullptr || (MSSAUpdater != nullptr && MSSA != nullptr)) &&
          "Unexpected input to sinkRegion");
 
   // We want to visit children before parents. We will enque all the parents
@@ -381,7 +430,10 @@
       if (isInstructionTriviallyDead(&I, TLI)) {
         DEBUG(dbgs() << "LICM deleting dead inst: " << I << '\n');
         ++II;
-        CurAST->deleteValue(&I);
+        if (CurAST)
+          CurAST->deleteValue(&I);
+        if (MSSA)
+          removeFromMSSA(&I, MSSAUpdater, MSSA);
         I.eraseFromParent();
         Changed = true;
         continue;
@@ -393,9 +445,11 @@
       // operands of the instruction are loop invariant.
       //
       if (isNotUsedInLoop(I, CurLoop, SafetyInfo) &&
-          canSinkOrHoistInst(I, AA, DT, CurLoop, CurAST, SafetyInfo, ORE)) {
+          canSinkOrHoistInst(I, AA, DT, CurLoop, CurAST, MSSAUpdater, MSSA,
+                             SafetyInfo, ORE)) {
         ++II;
-        Changed |= sink(I, LI, DT, CurLoop, CurAST, SafetyInfo, ORE);
+        Changed |= sink(I, LI, DT, CurLoop, CurAST, MSSAUpdater, MSSA,
+                        SafetyInfo, ORE);
       }
     }
   }
@@ -409,11 +463,14 @@
 ///
 bool llvm::hoistRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
                        DominatorTree *DT, TargetLibraryInfo *TLI, Loop *CurLoop,
-                       AliasSetTracker *CurAST, LoopSafetyInfo *SafetyInfo,
+                       AliasSetTracker *CurAST, MemorySSAUpdater *MSSAUpdater,
+                       MemorySSA *MSSA, LoopSafetyInfo *SafetyInfo,
                        OptimizationRemarkEmitter *ORE) {
   // Verify inputs.
   assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr &&
-         CurLoop != nullptr && CurAST != nullptr && SafetyInfo != nullptr &&
+         CurLoop != nullptr && SafetyInfo != nullptr &&
+         "Unexpected input to hoistRegion");
+  assert((CurAST != nullptr || (MSSAUpdater != nullptr && MSSA != nullptr)) &&
          "Unexpected input to hoistRegion");
 
   // We want to visit parents before children. We will enque all the parents
@@ -434,10 +491,17 @@
         if (Constant *C = ConstantFoldInstruction(
                 &I, I.getModule()->getDataLayout(), TLI)) {
           DEBUG(dbgs() << "LICM folding inst: " << I << "  --> " << *C << '\n');
-          CurAST->copyValue(&I, C);
+          if (CurAST)
+            CurAST->copyValue(&I, C);
+          // TODO: update sets if built beforehand; otherwise, no-op
+          if (MSSA) {
+          }
           I.replaceAllUsesWith(C);
           if (isInstructionTriviallyDead(&I, TLI)) {
-            CurAST->deleteValue(&I);
+            if (CurAST)
+              CurAST->deleteValue(&I);
+            if (MSSA)
+              removeFromMSSA(&I, MSSAUpdater, MSSA);
             I.eraseFromParent();
           }
           Changed = true;
@@ -462,7 +526,8 @@
           I.replaceAllUsesWith(Product);
           I.eraseFromParent();
 
-          hoist(*ReciprocalDivisor, DT, CurLoop, SafetyInfo, ORE);
+          hoist(*ReciprocalDivisor, DT, CurLoop, MSSAUpdater, MSSA, SafetyInfo,
+                ORE);
           Changed = true;
           continue;
         }
@@ -472,11 +537,12 @@
         // if it is safe to hoist the instruction.
         //
         if (CurLoop->hasLoopInvariantOperands(&I) &&
-            canSinkOrHoistInst(I, AA, DT, CurLoop, CurAST, SafetyInfo, ORE) &&
+            canSinkOrHoistInst(I, AA, DT, CurLoop, CurAST, MSSAUpdater, MSSA,
+                               SafetyInfo, ORE) &&
             isSafeToExecuteUnconditionally(
                 I, DT, CurLoop, SafetyInfo, ORE,
                 CurLoop->getLoopPreheader()->getTerminator()))
-          Changed |= hoist(I, DT, CurLoop, SafetyInfo, ORE);
+          Changed |= hoist(I, DT, CurLoop, MSSAUpdater, MSSA, SafetyInfo, ORE);
       }
   }
 
@@ -575,6 +641,7 @@
 
 bool llvm::canSinkOrHoistInst(Instruction &I, AAResults *AA, DominatorTree *DT,
                               Loop *CurLoop, AliasSetTracker *CurAST,
+                              MemorySSAUpdater *MSSAUpdater, MemorySSA *MSSA,
                               LoopSafetyInfo *SafetyInfo,
                               OptimizationRemarkEmitter *ORE) {
   // Loads have extra constraints we have to verify before we can hoist them.
@@ -601,8 +668,14 @@
     AAMDNodes AAInfo;
     LI->getAAMetadata(AAInfo);
 
-    bool Invalidated =
-        pointerInvalidatedByLoop(LI->getOperand(0), Size, AAInfo, CurAST);
+    bool Invalidated = false;
+    if (CurAST)
+      Invalidated =
+          pointerInvalidatedByLoop(LI->getOperand(0), Size, AAInfo, CurAST);
+    else // if (MSSA)
+      Invalidated = pointerInvalidatedByLoopWithMSSA(
+          LI->getOperand(0), MSSA, MSSA->getMemoryAccess(LI), CurLoop);
+
     // Check loop-invariant address because this may also be a sinkable load
     // whose address is not necessarily loop-invariant.
     if (ORE && Invalidated && CurLoop->isLoopInvariant(LI->getPointerOperand()))
@@ -630,20 +703,38 @@
       // it's arguments with arbitrary offsets.  If we can prove there are no
       // writes to this memory in the loop, we can hoist or sink.
       if (AliasAnalysis::onlyAccessesArgPointees(Behavior)) {
-        for (Value *Op : CI->arg_operands())
-          if (Op->getType()->isPointerTy() &&
-              pointerInvalidatedByLoop(Op, MemoryLocation::UnknownSize,
-                                       AAMDNodes(), CurAST))
+        for (Value *Op : CI->arg_operands()) {
+          bool Invalidated = false;
+          if (CurAST)
+            Invalidated = pointerInvalidatedByLoop(
+                Op, MemoryLocation::UnknownSize, AAMDNodes(), CurAST);
+          else // if (MSSA)
+            Invalidated = pointerInvalidatedByLoopWithMSSA(
+                Op, MSSA, MSSA->getMemoryAccess(CI), CurLoop);
+          if (Op->getType()->isPointerTy() && Invalidated)
             return false;
+        }
         return true;
       }
       // If this call only reads from memory and there are no writes to memory
       // in the loop, we can hoist or sink the call as appropriate.
       bool FoundMod = false;
-      for (AliasSet &AS : *CurAST) {
-        if (!AS.isForwardingAliasSet() && AS.isMod()) {
-          FoundMod = true;
-          break;
+      if (CurAST) {
+        for (AliasSet &AS : *CurAST) {
+          if (!AS.isForwardingAliasSet() && AS.isMod()) {
+            FoundMod = true;
+            break;
+          }
+        }
+      } else if (MSSA) {
+        // TODO: need "if this call only reads from memory"
+        for (auto BBIt = (CurLoop->block_begin()); BBIt != CurLoop->block_end();
+             BBIt++) {
+          auto *Defs = MSSA->getBlockDefs(*BBIt);
+          if (Defs) {
+            FoundMod = true;
+            break;
+          }
         }
       }
       if (!FoundMod)
@@ -739,6 +830,7 @@
 
 static Instruction *
 CloneInstructionInExitBlock(Instruction &I, BasicBlock &ExitBlock, PHINode &PN,
+                            MemorySSAUpdater *MSSAUpdater, MemorySSA *MSSA,
                             const LoopInfo *LI,
                             const LoopSafetyInfo *SafetyInfo) {
   Instruction *New;
@@ -776,6 +868,23 @@
   if (!I.getName().empty())
     New->setName(I.getName() + ".le");
 
+  MemoryAccess *OldMemAcc;
+  if (MSSA && (OldMemAcc = MSSA->getMemoryAccess(&I))) {
+    MemoryAccess *NewMemAcc = MSSAUpdater->createMemoryAccessInBB(
+        New, nullptr, New->getParent(), MemorySSA::Beginning);
+    MemoryDef *NewMemDef = dyn_cast_or_null<MemoryDef>(NewMemAcc);
+    if (NewMemDef)
+      MSSAUpdater->insertDef(NewMemDef, true);
+    else {
+      MemoryUse *NewMemUse = dyn_cast_or_null<MemoryUse>(NewMemAcc);
+      if (NewMemUse) {
+        MSSAUpdater->insertUse(NewMemUse);
+        // This is only called to properly update the defining access
+        MSSA->getWalker()->getClobberingMemoryAccess(NewMemUse);
+      }
+    }
+  }
+
   // Build LCSSA PHI nodes for any in-loop operands. Note that this is
   // particularly cheap because we can rip off the PHI node that we're
   // replacing for the number and blocks of the predecessors.
@@ -805,6 +914,7 @@
 ///
 static bool sink(Instruction &I, const LoopInfo *LI, const DominatorTree *DT,
                  const Loop *CurLoop, AliasSetTracker *CurAST,
+                 MemorySSAUpdater *MSSAUpdater, MemorySSA *MSSA,
                  const LoopSafetyInfo *SafetyInfo,
                  OptimizationRemarkEmitter *ORE) {
   DEBUG(dbgs() << "LICM sinking instruction: " << I << "\n");
@@ -860,14 +970,17 @@
     if (It != SunkCopies.end())
       New = It->second;
     else
-      New = SunkCopies[ExitBlock] =
-          CloneInstructionInExitBlock(I, *ExitBlock, *PN, LI, SafetyInfo);
+      New = SunkCopies[ExitBlock] = CloneInstructionInExitBlock(
+          I, *ExitBlock, *PN, MSSAUpdater, MSSA, LI, SafetyInfo);
 
     PN->replaceAllUsesWith(New);
     PN->eraseFromParent();
   }
 
-  CurAST->deleteValue(&I);
+  if (CurAST)
+    CurAST->deleteValue(&I);
+  if (MSSA)
+    removeFromMSSA(&I, MSSAUpdater, MSSA);
   I.eraseFromParent();
   return Changed;
 }
@@ -876,6 +989,7 @@
 /// is safe to hoist, this instruction is called to do the dirty work.
 ///
 static bool hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
+                  MemorySSAUpdater *MSSAUpdater, MemorySSA *MSSA,
                   const LoopSafetyInfo *SafetyInfo,
                   OptimizationRemarkEmitter *ORE) {
   auto *Preheader = CurLoop->getLoopPreheader();
@@ -897,6 +1011,16 @@
 
   // Move the new node to the Preheader, before its terminator.
   I.moveBefore(Preheader->getTerminator());
+  if (MSSA) {
+    // Update MemorySSA if moving I just moved a load or store
+    MemoryUseOrDef *OldMemAcc =
+        dyn_cast_or_null<MemoryUseOrDef>(MSSA->getMemoryAccess(&I));
+    if (OldMemAcc) {
+      MSSAUpdater->moveToPlace(OldMemAcc, Preheader, MemorySSA::End);
+      // This is only called to properly update the defining access
+      MSSA->getWalker()->getClobberingMemoryAccess(OldMemAcc);
+    }
+  }
 
   // Do not retain debug locations when we are moving instructions to different
   // basic blocks, because we want to avoid jumpy line tables. Calls, however,
@@ -948,7 +1072,11 @@
   SmallVectorImpl<BasicBlock *> &LoopExitBlocks;
   SmallVectorImpl<Instruction *> &LoopInsertPts;
   PredIteratorCache &PredCache;
-  AliasSetTracker &AST;
+
+  // AST and AS are alternatives!
+  AliasSetTracker *AST;
+  MemorySSAAliasSets *AS;
+
   LoopInfo &LI;
   DebugLoc DL;
   int Alignment;
@@ -975,11 +1103,12 @@
                const SmallSetVector<Value *, 8> &PMA,
                SmallVectorImpl<BasicBlock *> &LEB,
                SmallVectorImpl<Instruction *> &LIP, PredIteratorCache &PIC,
-               AliasSetTracker &ast, LoopInfo &li, DebugLoc dl, int alignment,
-               bool UnorderedAtomic, const AAMDNodes &AATags)
+               AliasSetTracker *ast, MemorySSAAliasSets *as, LoopInfo &li,
+               DebugLoc dl, int alignment, bool UnorderedAtomic,
+               const AAMDNodes &AATags)
       : LoadAndStorePromoter(Insts, S), SomePtr(SP), PointerMustAliases(PMA),
         LoopExitBlocks(LEB), LoopInsertPts(LIP), PredCache(PIC), AST(ast),
-        LI(li), DL(std::move(dl)), Alignment(alignment),
+        AS(as), LI(li), DL(std::move(dl)), Alignment(alignment),
         UnorderedAtomic(UnorderedAtomic), AATags(AATags) {}
 
   bool isInstInList(Instruction *I,
@@ -1010,14 +1139,36 @@
       NewSI->setDebugLoc(DL);
       if (AATags)
         NewSI->setAAMetadata(AATags);
+      if (AS) {
+        MemoryAccess *MSSAInsertPoint = AS->getInsertPoint(i);
+        MemoryAccess *NewMemAcc;
+        if (!MSSAInsertPoint) {
+          NewMemAcc = AS->MSSAUpdater->createMemoryAccessInBB(
+              NewSI, nullptr, NewSI->getParent(), MemorySSA::Beginning);
+        } else {
+          NewMemAcc = AS->MSSAUpdater->createMemoryAccessAfter(NewSI, nullptr,
+                                                               MSSAInsertPoint);
+        }
+        AS->setInsertPoint(NewMemAcc, i);
+        AS->MSSAUpdater->insertDef(cast<MemoryDef>(NewMemAcc), true);
+        // FIXME: true for safety, false may still be correct.
+      }
     }
   }
 
   void replaceLoadWithValue(LoadInst *LI, Value *V) const override {
     // Update alias analysis.
-    AST.copyValue(LI, V);
+    if (AST)
+      AST->copyValue(LI, V);
+    if (AS)
+      AS->replace(LI, V);
+  }
+  void instructionDeleted(Instruction *I) const override {
+    if (AST)
+      AST->deleteValue(I);
+    if (AS)
+      removeFromMSSA(I, AS->MSSAUpdater, AS->MSSA);
   }
-  void instructionDeleted(Instruction *I) const override { AST.deleteValue(I); }
 };
 } // namespace
 
@@ -1031,12 +1182,14 @@
     SmallVectorImpl<BasicBlock *> &ExitBlocks,
     SmallVectorImpl<Instruction *> &InsertPts, PredIteratorCache &PIC,
     LoopInfo *LI, DominatorTree *DT, const TargetLibraryInfo *TLI,
-    Loop *CurLoop, AliasSetTracker *CurAST, LoopSafetyInfo *SafetyInfo,
-    OptimizationRemarkEmitter *ORE) {
+    Loop *CurLoop, AliasSetTracker *CurAST, MemorySSAAliasSets *AS,
+    LoopSafetyInfo *SafetyInfo, OptimizationRemarkEmitter *ORE) {
   // Verify inputs.
   assert(LI != nullptr && DT != nullptr && CurLoop != nullptr &&
-         CurAST != nullptr && SafetyInfo != nullptr &&
+         SafetyInfo != nullptr &&
          "Unexpected Input to promoteLoopAccessesToScalars");
+  assert((CurAST != nullptr || (AS != nullptr)) &&
+         "Unexpected input to promoteLoopAccessesToScalars");
 
   Value *SomePtr = *PointerMustAliases.begin();
   BasicBlock *Preheader = CurLoop->getLoopPreheader();
@@ -1266,7 +1419,7 @@
   SmallVector<PHINode *, 16> NewPHIs;
   SSAUpdater SSA(&NewPHIs);
   LoopPromoter Promoter(SomePtr, LoopUses, SSA, PointerMustAliases, ExitBlocks,
-                        InsertPts, PIC, *CurAST, *LI, DL, Alignment,
+                        InsertPts, PIC, CurAST, AS, *LI, DL, Alignment,
                         SawUnorderedAtomic, AATags);
 
   // Set up the preheader to have a definition of the value.  It is the live-out
@@ -1281,13 +1434,27 @@
     PreheaderLoad->setAAMetadata(AATags);
   SSA.AddAvailableValue(Preheader, PreheaderLoad);
 
+  MemoryAccess *PreheaderLoadMemoryAccess;
+  if (AS) {
+    // Update MSSA
+    PreheaderLoadMemoryAccess = AS->MSSAUpdater->createMemoryAccessInBB(
+        PreheaderLoad, nullptr, PreheaderLoad->getParent(), MemorySSA::End);
+    MemoryUse *NewMemUse = cast<MemoryUse>(PreheaderLoadMemoryAccess);
+    AS->MSSAUpdater->insertUse(NewMemUse);
+    // This is only called to properly update the defining access
+    AS->MSSA->getWalker()->getClobberingMemoryAccess(NewMemUse);
+  }
+
   // Rewrite all the loads in the loop and remember all the definitions from
   // stores in the loop.
   Promoter.run(LoopUses);
 
   // If the SSAUpdater didn't use the load in the preheader, just zap it now.
-  if (PreheaderLoad->use_empty())
+  if (PreheaderLoad->use_empty()) {
+    if (AS)
+      AS->MSSAUpdater->removeMemoryAccess(PreheaderLoadMemoryAccess);
     PreheaderLoad->eraseFromParent();
+  }
 
   return true;
 }
@@ -1387,6 +1554,75 @@
   return CurAST->getAliasSetForPointer(V, Size, AAInfo).isMod();
 }
 
+// Checks arguments of a Phi, so Defs and other Phis.
+// returns true if Acc is not a load or a live on entry
+static bool checkNotLoadOrLOE(MemoryAccess *Acc, MemorySSA *MSSA,
+                              SmallPtrSetImpl<MemoryAccess *> &Processed) {
+  if (Processed.count(Acc))
+    return true;
+  if (MSSA->isLiveOnEntryDef(Acc))
+    return false;
+
+  MemoryPhi *Phi = dyn_cast_or_null<MemoryPhi>(Acc);
+  MemoryDef *Def = dyn_cast_or_null<MemoryDef>(Acc);
+  if (Phi) {
+    bool MSSAResult = false;
+    int NoArgsPhi = Phi->getNumIncomingValues();
+    Processed.insert(Acc);
+    for (int I = 0; I < NoArgsPhi; I++) {
+      MemoryAccess *Arg = Phi->getIncomingValue(I);
+      MSSAResult |= checkNotLoadOrLOE(Arg, MSSA, Processed);
+    }
+    return MSSAResult;
+  } else if (Def) {
+    Instruction *AccI = Def->getMemoryInst();
+    if (AccI && isa<LoadInst>(AccI)) // a load is a def if volatile
+      return false;
+  }
+  return true;
+}
+
+static bool pointerInvalidatedByLoopWithMSSAHelper(MemorySSA *MSSA,
+                                                   MemoryUseOrDef *MUD,
+                                                   Loop *CurLoop) {
+  bool MSSAResult = false;
+  MemoryUse *MU = nullptr;
+  // MUD is from a LoopInstr or CallInstr, so both Uses.
+  if (MUD && (MU = dyn_cast_or_null<MemoryUse>(MUD))) {
+    // BIG NOTE: getDefiningAccess may not be precise, since optimizeUses
+    // in MemorySSA is capped. This is good! It means that this becomes best
+    // effort, rather than incur a performance penalty for loops with large load
+    // count. Perfect accuracy can be obtained with:
+    // MSSA->getWalker()->getClobberingMemoryAccess(MU)
+    // For the updates done by sink/hoist/promotion (insertUse, moveToPlace),
+    // we *explicitly* call getClobberingMemoryAccesses. This will get perfect
+    // results for small tests, and imprecise but fast for large ones.
+    // MemoryAccess *Source = MSSA->getWalker()->getClobberingMemoryAccess(MU);
+    MemoryAccess *Source = MU->getDefiningAccess();
+
+    if (MSSA->isLiveOnEntryDef(Source)) {
+      MSSAResult = false;
+    } else {
+      BasicBlock *DBB = Source->getBlock();
+      if (CurLoop->contains(DBB)) {
+        // if the Source is a combination of liveOnEntry and
+        // volatile loads (treated as Defs), it's not invalidated.
+        SmallPtrSet<MemoryAccess *, 4> Processed;
+        MSSAResult = checkNotLoadOrLOE(Source, MSSA, Processed);
+      }
+    }
+  }
+  return MSSAResult;
+}
+static bool pointerInvalidatedByLoopWithMSSA(Value *V, MemorySSA *MSSA,
+                                             MemoryUseOrDef *MUD,
+                                             Loop *CurLoop) {
+  if (isa<UndefValue>(V))
+    return true;
+  bool MSSAResult = pointerInvalidatedByLoopWithMSSAHelper(MSSA, MUD, CurLoop);
+  return MSSAResult;
+}
+
 /// Little predicate that returns true if the specified basic block is in
 /// a subloop of the current one, not the current one itself.
 ///
@@ -1394,3 +1630,11 @@
   assert(CurLoop->contains(BB) && "Only valid if BB is IN the loop");
   return LI->getLoopFor(BB) != CurLoop;
 }
+
+static void removeFromMSSA(Instruction *I, MemorySSAUpdater *MSSAUpdater,
+                           MemorySSA *MSSA) {
+  MemoryUseOrDef *AccI = MSSA->getMemoryAccess(I);
+  if (AccI) {
+    MSSAUpdater->removeMemoryAccess(AccI);
+  }
+}
Index: lib/Transforms/Scalar/LoopDistribute.cpp
===================================================================
--- lib/Transforms/Scalar/LoopDistribute.cpp
+++ lib/Transforms/Scalar/LoopDistribute.cpp
@@ -31,6 +31,7 @@
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/LoopAccessAnalysis.h"
 #include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/MemorySSA.h"
 #include "llvm/Analysis/OptimizationDiagnosticInfo.h"
 #include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/IR/Dominators.h"
@@ -952,11 +953,12 @@
   auto &AC = AM.getResult<AssumptionAnalysis>(F);
   auto &TTI = AM.getResult<TargetIRAnalysis>(F);
   auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
+  auto &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA();
 
   auto &LAM = AM.getResult<LoopAnalysisManagerFunctionProxy>(F).getManager();
   std::function<const LoopAccessInfo &(Loop &)> GetLAA =
       [&](Loop &L) -> const LoopAccessInfo & {
-    LoopStandardAnalysisResults AR = {AA, AC, DT, LI, SE, TLI, TTI};
+    LoopStandardAnalysisResults AR = {AA, AC, DT, LI, SE, TLI, TTI, MSSA};
     return LAM.getResult<LoopAccessAnalysis>(L, AR);
   };
 
Index: lib/Transforms/Scalar/LoopLoadElimination.cpp
===================================================================
--- lib/Transforms/Scalar/LoopLoadElimination.cpp
+++ lib/Transforms/Scalar/LoopLoadElimination.cpp
@@ -31,6 +31,7 @@
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/LoopAccessAnalysis.h"
 #include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/MemorySSA.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Analysis/ScalarEvolutionExpander.h"
 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
@@ -648,11 +649,12 @@
   auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
   auto &AA = AM.getResult<AAManager>(F);
   auto &AC = AM.getResult<AssumptionAnalysis>(F);
+  auto &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA();
 
   auto &LAM = AM.getResult<LoopAnalysisManagerFunctionProxy>(F).getManager();
   bool Changed = eliminateLoadsAcrossLoops(
       F, LI, DT, [&](Loop &L) -> const LoopAccessInfo & {
-        LoopStandardAnalysisResults AR = {AA, AC, DT, LI, SE, TLI, TTI};
+        LoopStandardAnalysisResults AR = {AA, AC, DT, LI, SE, TLI, TTI, MSSA};
         return LAM.getResult<LoopAccessAnalysis>(L, AR);
       });
 
Index: lib/Transforms/Scalar/LoopSink.cpp
===================================================================
--- lib/Transforms/Scalar/LoopSink.cpp
+++ lib/Transforms/Scalar/LoopSink.cpp
@@ -288,7 +288,8 @@
     // No need to check for instruction's operands are loop invariant.
     assert(L.hasLoopInvariantOperands(I) &&
            "Insts in a loop's preheader should have loop invariant operands!");
-    if (!canSinkOrHoistInst(*I, &AA, &DT, &L, &CurAST, nullptr))
+    if (!canSinkOrHoistInst(*I, &AA, &DT, &L, &CurAST, nullptr, nullptr,
+                            nullptr, nullptr))
       continue;
     if (sinkInstruction(L, *I, ColdLoopBBs, LoopBlockNumber, LI, DT, BFI))
       Changed = true;
Index: lib/Transforms/Utils/LoopUtils.cpp
===================================================================
--- lib/Transforms/Utils/LoopUtils.cpp
+++ lib/Transforms/Utils/LoopUtils.cpp
@@ -1119,12 +1119,12 @@
 /// Does a BFS from a given node to all of its children inside a given loop.
 /// The returned vector of nodes includes the starting point.
 SmallVector<DomTreeNode *, 16>
-llvm::collectChildrenInLoop(DomTreeNode *N, const Loop *CurLoop) {
+llvm::collectChildrenInLoop(DomTreeNode *N, Loop *CurLoop) {
   SmallVector<DomTreeNode *, 16> Worklist;
   auto AddRegionToWorklist = [&](DomTreeNode *DTN) {
     // Only include subregions in the top level loop.
     BasicBlock *BB = DTN->getBlock();
-    if (CurLoop->contains(BB))
+    if (!CurLoop || CurLoop->contains(BB))
       Worklist.push_back(DTN);
   };
 
Index: lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- lib/Transforms/Vectorize/LoopVectorize.cpp
+++ lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -8710,11 +8710,12 @@
     auto &AC = AM.getResult<AssumptionAnalysis>(F);
     auto &DB = AM.getResult<DemandedBitsAnalysis>(F);
     auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
+    auto &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA();
 
     auto &LAM = AM.getResult<LoopAnalysisManagerFunctionProxy>(F).getManager();
     std::function<const LoopAccessInfo &(Loop &)> GetLAA =
         [&](Loop &L) -> const LoopAccessInfo & {
-      LoopStandardAnalysisResults AR = {AA, AC, DT, LI, SE, TLI, TTI};
+      LoopStandardAnalysisResults AR = {AA, AC, DT, LI, SE, TLI, TTI, MSSA};
       return LAM.getResult<LoopAccessAnalysis>(L, AR);
     };
     bool Changed =
Index: test/Other/loop-pm-invalidation.ll
===================================================================
--- test/Other/loop-pm-invalidation.ll
+++ test/Other/loop-pm-invalidation.ll
@@ -51,6 +51,7 @@
 ; CHECK-LOOP-INV-NEXT: Running analysis: TargetLibraryAnalysis
 ; CHECK-LOOP-INV-NEXT: Running analysis: ScalarEvolutionAnalysis
 ; CHECK-LOOP-INV-NEXT: Running analysis: TargetIRAnalysis
+; CHECK-LOOP-INV-NEXT: Running analysis: MemorySSAAnalysis
 ; CHECK-LOOP-INV-NEXT: Running analysis: InnerAnalysisManagerProxy<{{.*}}Loop
 ; CHECK-LOOP-INV-NEXT: Starting {{.*}}Loop pass manager run.
 ; CHECK-LOOP-INV-NEXT: Running pass: NoOpLoopPass
@@ -78,6 +79,7 @@
 ; CHECK-SCEV-INV-NEXT: Running analysis: TargetLibraryAnalysis
 ; CHECK-SCEV-INV-NEXT: Running analysis: ScalarEvolutionAnalysis
 ; CHECK-SCEV-INV-NEXT: Running analysis: TargetIRAnalysis
+; CHECK-SCEV-INV-NEXT: Running analysis: MemorySSAAnalysis
 ; CHECK-SCEV-INV-NEXT: Running analysis: InnerAnalysisManagerProxy<{{.*}}Loop
 ; CHECK-SCEV-INV-NEXT: Starting {{.*}}Loop pass manager run.
 ; CHECK-SCEV-INV-NEXT: Running pass: NoOpLoopPass
@@ -115,6 +117,7 @@
 ; CHECK-LOOP-INV-NEXT: Running analysis: TargetLibraryAnalysis
 ; CHECK-LOOP-INV-NEXT: Running analysis: ScalarEvolutionAnalysis
 ; CHECK-LOOP-INV-NEXT: Running analysis: TargetIRAnalysis
+; CHECK-LOOP-INV-NEXT: Running analysis: MemorySSAAnalysis
 ; CHECK-LOOP-INV-NEXT: Running analysis: InnerAnalysisManagerProxy<{{.*}}Loop
 ; CHECK-LOOP-INV-NEXT: Starting {{.*}}Loop pass manager run.
 ; CHECK-LOOP-INV-NEXT: Running pass: NoOpLoopPass
@@ -149,6 +152,7 @@
 ; CHECK-SCEV-INV-NEXT: Running analysis: TargetLibraryAnalysis
 ; CHECK-SCEV-INV-NEXT: Running analysis: ScalarEvolutionAnalysis
 ; CHECK-SCEV-INV-NEXT: Running analysis: TargetIRAnalysis
+; CHECK-SCEV-INV-NEXT: Running analysis: MemorySSAAnalysis
 ; CHECK-SCEV-INV-NEXT: Running analysis: InnerAnalysisManagerProxy<{{.*}}Loop
 ; CHECK-SCEV-INV-NEXT: Starting {{.*}}Loop pass manager run.
 ; CHECK-SCEV-INV-NEXT: Running pass: NoOpLoopPass
@@ -200,6 +204,7 @@
 ; CHECK-LOOP-INV-NEXT: Running analysis: TargetLibraryAnalysis
 ; CHECK-LOOP-INV-NEXT: Running analysis: ScalarEvolutionAnalysis
 ; CHECK-LOOP-INV-NEXT: Running analysis: TargetIRAnalysis
+; CHECK-LOOP-INV-NEXT: Running analysis: MemorySSAAnalysis
 ; CHECK-LOOP-INV-NEXT: Running analysis: InnerAnalysisManagerProxy<{{.*}}Loop
 ; CHECK-LOOP-INV-NEXT: Starting {{.*}}Loop pass manager run.
 ; CHECK-LOOP-INV-NEXT: Running pass: NoOpLoopPass
@@ -227,6 +232,7 @@
 ; CHECK-SCEV-INV-NEXT: Running analysis: TargetLibraryAnalysis
 ; CHECK-SCEV-INV-NEXT: Running analysis: ScalarEvolutionAnalysis
 ; CHECK-SCEV-INV-NEXT: Running analysis: TargetIRAnalysis
+; CHECK-SCEV-INV-NEXT: Running analysis: MemorySSAAnalysis
 ; CHECK-SCEV-INV-NEXT: Running analysis: InnerAnalysisManagerProxy<{{.*}}Loop
 ; CHECK-SCEV-INV-NEXT: Starting {{.*}}Loop pass manager run.
 ; CHECK-SCEV-INV-NEXT: Running pass: NoOpLoopPass
@@ -252,6 +258,7 @@
 ; CHECK-SCEV-INV-AFTER-DELETE-NEXT: Running analysis: TargetLibraryAnalysis
 ; CHECK-SCEV-INV-AFTER-DELETE-NEXT: Running analysis: ScalarEvolutionAnalysis
 ; CHECK-SCEV-INV-AFTER-DELETE-NEXT: Running analysis: TargetIRAnalysis
+; CHECK-SCEV-INV-AFTER-DELETE-NEXT: Running analysis: MemorySSAAnalysis
 ; CHECK-SCEV-INV-AFTER-DELETE-NEXT: Running analysis: InnerAnalysisManagerProxy<{{.*}}Loop
 ; CHECK-SCEV-INV-AFTER-DELETE-NEXT: Starting {{.*}}Loop pass manager run.
 ; CHECK-SCEV-INV-AFTER-DELETE-NEXT: Running pass: NoOpLoopPass
@@ -259,6 +266,7 @@
 ; CHECK-SCEV-INV-AFTER-DELETE-NEXT: Clearing all analysis results for:
 ; CHECK-SCEV-INV-AFTER-DELETE-NEXT: Finished {{.*}}Loop pass manager run.
 ; CHECK-SCEV-INV-AFTER-DELETE-NEXT: Invalidating all non-preserved analyses
+; CHECK-SCEV-INV-AFTER-DELETE-NEXT: Invalidating analysis: MemorySSAAnalysis
 ; CHECK-SCEV-INV-AFTER-DELETE-NEXT: Running pass: InvalidateAnalysisPass<{{.*}}ScalarEvolutionAnalysis
 ; CHECK-SCEV-INV-AFTER-DELETE-NEXT: Invalidating all non-preserved analyses
 ; CHECK-SCEV-INV-AFTER-DELETE-NEXT: Invalidating analysis: ScalarEvolutionAnalysis
Index: test/Other/new-pass-manager.ll
===================================================================
--- test/Other/new-pass-manager.ll
+++ test/Other/new-pass-manager.ll
@@ -458,6 +458,7 @@
 ; CHECK-REPEAT-LOOP-PASS-NEXT: Running analysis: TargetLibraryAnalysis
 ; CHECK-REPEAT-LOOP-PASS-NEXT: Running analysis: ScalarEvolutionAnalysis
 ; CHECK-REPEAT-LOOP-PASS-NEXT: Running analysis: TargetIRAnalysis
+; CHECK-REPEAT-LOOP-PASS-NEXT: Running analysis: MemorySSAAnalysis
 ; CHECK-REPEAT-LOOP-PASS-NEXT: Running analysis: InnerAnalysisManagerProxy<{{.*}}>
 ; CHECK-REPEAT-LOOP-PASS-NEXT: Starting Loop pass manager run
 ; CHECK-REPEAT-LOOP-PASS-NEXT: Running pass: RepeatedPass
Index: test/Other/pass-pipelines.ll
===================================================================
--- test/Other/pass-pipelines.ll
+++ test/Other/pass-pipelines.ll
@@ -37,6 +37,9 @@
 ; CHECK-O2-NEXT: FunctionPass Manager
 ; CHECK-O2-NOT: Manager
 ; CHECK-O2: Loop Pass Manager
+; FIXME: Adition of MemorySSA splits the Loop Pass Manager into 3.
+; CHECK-O2: Loop Pass Manager
+; CHECK-O2: Loop Pass Manager
 ; CHECK-O2-NOT: Manager
 ; FIXME: We shouldn't be pulling out to simplify-cfg and instcombine and
 ; causing new loop pass managers.
Index: unittests/Transforms/Scalar/LoopPassManagerTest.cpp
===================================================================
--- unittests/Transforms/Scalar/LoopPassManagerTest.cpp
+++ unittests/Transforms/Scalar/LoopPassManagerTest.cpp
@@ -304,6 +304,7 @@
     // those.
     FAM.registerPass([&] { return AAManager(); });
     FAM.registerPass([&] { return AssumptionAnalysis(); });
+    FAM.registerPass([&] { return MemorySSAAnalysis(); });
     FAM.registerPass([&] { return ScalarEvolutionAnalysis(); });
     FAM.registerPass([&] { return TargetLibraryAnalysis(); });
     FAM.registerPass([&] { return TargetIRAnalysis(); });