diff --git a/llvm/include/llvm/Analysis/IVDescriptors.h b/llvm/include/llvm/Analysis/IVDescriptors.h
--- a/llvm/include/llvm/Analysis/IVDescriptors.h
+++ b/llvm/include/llvm/Analysis/IVDescriptors.h
@@ -26,6 +26,7 @@
 class DominatorTree;
 class Instruction;
 class Loop;
+class MemoryDependenceResults;
 class PredicatedScalarEvolution;
 class ScalarEvolution;
 class SCEV;
@@ -193,7 +194,8 @@
   static bool
   isFixedOrderRecurrence(PHINode *Phi, Loop *TheLoop,
                          MapVector<Instruction *, Instruction *> &SinkAfter,
-                         DominatorTree *DT);
+                         DominatorTree *DT,
+                         MemoryDependenceResults *MDR);
 
   RecurKind getRecurrenceKind() const { return Kind; }
 
diff --git a/llvm/include/llvm/Transforms/Vectorize/LoopVectorizationLegality.h b/llvm/include/llvm/Transforms/Vectorize/LoopVectorizationLegality.h
--- a/llvm/include/llvm/Transforms/Vectorize/LoopVectorizationLegality.h
+++ b/llvm/include/llvm/Transforms/Vectorize/LoopVectorizationLegality.h
@@ -41,6 +41,7 @@
 class Function;
 class Loop;
 class LoopInfo;
+class MemoryDependenceResults;
 class Metadata;
 class OptimizationRemarkEmitter;
 class PredicatedScalarEvolution;
@@ -247,10 +248,11 @@
                             OptimizationRemarkEmitter *ORE,
                             LoopVectorizationRequirements *R,
                             LoopVectorizeHints *H, DemandedBits *DB,
-                            AssumptionCache *AC, BlockFrequencyInfo *BFI,
+                            AssumptionCache *AC, MemoryDependenceResults *MDR,
+                            BlockFrequencyInfo *BFI,
                             ProfileSummaryInfo *PSI)
       : TheLoop(L), LI(LI), PSE(PSE), TTI(TTI), TLI(TLI), DT(DT), LAIs(LAIs),
-        ORE(ORE), Requirements(R), Hints(H), DB(DB), AC(AC), BFI(BFI),
+        ORE(ORE), Requirements(R), Hints(H), DB(DB), AC(AC), MDR(MDR), BFI(BFI),
         PSI(PSI) {}
 
   /// ReductionList contains the reduction descriptors for all
@@ -543,6 +545,10 @@
   /// which a reduction can be computed.
   AssumptionCache *AC;
 
+  // The memory dependence analysis is used to determine if stores can be
+  // reordered past loads for fixed order reductions.
+  MemoryDependenceResults *MDR;
+
   /// While vectorizing these instructions we have to generate a
   /// call to the appropriate masked intrinsic
   SmallPtrSet<const Instruction *, 8> MaskedOp;
diff --git a/llvm/include/llvm/Transforms/Vectorize/LoopVectorize.h b/llvm/include/llvm/Transforms/Vectorize/LoopVectorize.h
--- a/llvm/include/llvm/Transforms/Vectorize/LoopVectorize.h
+++ b/llvm/include/llvm/Transforms/Vectorize/LoopVectorize.h
@@ -71,6 +71,7 @@
 class Loop;
 class LoopAccessInfoManager;
 class LoopInfo;
+class MemoryDependenceResults;
 class OptimizationRemarkEmitter;
 class ProfileSummaryInfo;
 class ScalarEvolution;
@@ -179,6 +180,7 @@
   TargetLibraryInfo *TLI;
   DemandedBits *DB;
   AAResults *AA;
+  MemoryDependenceResults *MDR;
   AssumptionCache *AC;
   LoopAccessInfoManager *LAIs;
   OptimizationRemarkEmitter *ORE;
@@ -193,8 +195,9 @@
   runImpl(Function &F, ScalarEvolution &SE_, LoopInfo &LI_,
           TargetTransformInfo &TTI_, DominatorTree &DT_,
           BlockFrequencyInfo &BFI_, TargetLibraryInfo *TLI_, DemandedBits &DB_,
-          AAResults &AA_, AssumptionCache &AC_, LoopAccessInfoManager &LAIs_,
-          OptimizationRemarkEmitter &ORE_, ProfileSummaryInfo *PSI_);
+          AAResults &AA_, AssumptionCache &AC_, MemoryDependenceResults &MDR_,
+          LoopAccessInfoManager &LAIs_, OptimizationRemarkEmitter &ORE_,
+          ProfileSummaryInfo *PSI_);
 
   bool processLoop(Loop *L);
 };
diff --git a/llvm/lib/Analysis/IVDescriptors.cpp b/llvm/lib/Analysis/IVDescriptors.cpp
--- a/llvm/lib/Analysis/IVDescriptors.cpp
+++ b/llvm/lib/Analysis/IVDescriptors.cpp
@@ -13,6 +13,7 @@
 #include "llvm/Analysis/IVDescriptors.h"
 #include "llvm/Analysis/DemandedBits.h"
 #include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/MemoryDependenceAnalysis.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
 #include "llvm/Analysis/ValueTracking.h"
@@ -923,7 +924,8 @@
 
 bool RecurrenceDescriptor::isFixedOrderRecurrence(
     PHINode *Phi, Loop *TheLoop,
-    MapVector<Instruction *, Instruction *> &SinkAfter, DominatorTree *DT) {
+    MapVector<Instruction *, Instruction *> &SinkAfter, DominatorTree *DT,
+    MemoryDependenceResults *MDR) {
 
   // Ensure the phi node is in the loop header and has two incoming values.
   if (Phi->getParent() != TheLoop->getHeader() ||
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
--- a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
@@ -722,7 +722,7 @@
         }
 
         if (RecurrenceDescriptor::isFixedOrderRecurrence(Phi, TheLoop,
-                                                         SinkAfter, DT)) {
+                                                         SinkAfter, DT, MDR)) {
           AllowedExit.insert(Phi);
           FixedOrderRecurrences.insert(Phi);
           continue;
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -86,6 +86,7 @@
 #include "llvm/Analysis/LoopAnalysisManager.h"
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/LoopIterator.h"
+#include "llvm/Analysis/MemoryDependenceAnalysis.h"
 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
 #include "llvm/Analysis/ProfileSummaryInfo.h"
 #include "llvm/Analysis/ScalarEvolution.h"
@@ -2216,9 +2217,10 @@
     auto *DB = &getAnalysis<DemandedBitsWrapperPass>().getDemandedBits();
     auto *ORE = &getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE();
     auto *PSI = &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI();
+    auto *MDR = &getAnalysis<MemoryDependenceWrapperPass>().getMemDep();
 
     return Impl
-        .runImpl(F, *SE, *LI, *TTI, *DT, *BFI, TLI, *DB, *AA, *AC, LAIs, *ORE,
+        .runImpl(F, *SE, *LI, *TTI, *DT, *BFI, TLI, *DB, *AA, *AC, *MDR, LAIs, *ORE,
                  PSI)
         .MadeAnyChange;
   }
@@ -2235,6 +2237,7 @@
     AU.addRequired<DemandedBitsWrapperPass>();
     AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
     AU.addRequired<InjectTLIMappingsLegacy>();
+    AU.addRequired<MemoryDependenceWrapperPass>();
 
     // We currently do not preserve loopinfo/dominator analyses with outer loop
     // vectorization. Until this is addressed, mark these analyses as preserved
@@ -10181,7 +10184,7 @@
   // Check if it is legal to vectorize the loop.
   LoopVectorizationRequirements Requirements;
   LoopVectorizationLegality LVL(L, PSE, DT, TTI, TLI, AA, F, *LAIs, LI, ORE,
-                                &Requirements, &Hints, DB, AC, BFI, PSI);
+                                &Requirements, &Hints, DB, AC, MDR, BFI, PSI);
   if (!LVL.canVectorize(EnableVPlanNativePath)) {
     LLVM_DEBUG(dbgs() << "LV: Not vectorizing: Cannot prove legality.\n");
     Hints.emitRemarkWithHints();
@@ -10541,8 +10544,8 @@
     Function &F, ScalarEvolution &SE_, LoopInfo &LI_, TargetTransformInfo &TTI_,
     DominatorTree &DT_, BlockFrequencyInfo &BFI_, TargetLibraryInfo *TLI_,
     DemandedBits &DB_, AAResults &AA_, AssumptionCache &AC_,
-    LoopAccessInfoManager &LAIs_, OptimizationRemarkEmitter &ORE_,
-    ProfileSummaryInfo *PSI_) {
+    MemoryDependenceResults &MDR_, LoopAccessInfoManager &LAIs_,
+    OptimizationRemarkEmitter &ORE_, ProfileSummaryInfo *PSI_) {
   SE = &SE_;
   LI = &LI_;
   TTI = &TTI_;
@@ -10555,6 +10558,7 @@
   DB = &DB_;
   ORE = &ORE_;
   PSI = PSI_;
+  MDR = &MDR_;
 
   // Don't attempt if
   // 1. the target claims to have no vector registers, and
@@ -10619,13 +10623,14 @@
     auto &AC = AM.getResult<AssumptionAnalysis>(F);
     auto &DB = AM.getResult<DemandedBitsAnalysis>(F);
     auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
+    auto &MDA = AM.getResult<MemoryDependenceAnalysis>(F);
 
     LoopAccessInfoManager &LAIs = AM.getResult<LoopAccessAnalysis>(F);
     auto &MAMProxy = AM.getResult<ModuleAnalysisManagerFunctionProxy>(F);
     ProfileSummaryInfo *PSI =
         MAMProxy.getCachedResult<ProfileSummaryAnalysis>(*F.getParent());
     LoopVectorizeResult Result =
-        runImpl(F, SE, LI, TTI, DT, BFI, &TLI, DB, AA, AC, LAIs, ORE, PSI);
+        runImpl(F, SE, LI, TTI, DT, BFI, &TLI, DB, AA, AC, MDA, LAIs, ORE, PSI);
     if (!Result.MadeAnyChange)
       return PreservedAnalyses::all();
     PreservedAnalyses PA;
diff --git a/llvm/test/Other/new-pm-defaults.ll b/llvm/test/Other/new-pm-defaults.ll
--- a/llvm/test/Other/new-pm-defaults.ll
+++ b/llvm/test/Other/new-pm-defaults.ll
@@ -244,6 +244,8 @@
 ; CHECK-O-NEXT: Running pass: LoopVectorizePass
 ; CHECK-O-NEXT: Running analysis: BlockFrequencyAnalysis
 ; CHECK-O-NEXT: Running analysis: BranchProbabilityAnalysis
+; CHECK-O1-NEXT: Running analysis: MemoryDependenceAnalysis
+; CHECK-O1-NEXT: Running analysis: PhiValuesAnalysis
 ; CHECK-O-NEXT: Running pass: LoopLoadEliminationPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
diff --git a/llvm/test/Other/new-pm-thinlto-defaults.ll b/llvm/test/Other/new-pm-thinlto-defaults.ll
--- a/llvm/test/Other/new-pm-thinlto-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-defaults.ll
@@ -36,7 +36,7 @@
 ; Postlink pipelines:
 ; RUN: opt -disable-verify -verify-cfg-preserved=0 -eagerly-invalidate-analyses=0 -debug-pass-manager \
 ; RUN:     -passes='thinlto<O1>' -S %s 2>&1 \
-; RUN:     | FileCheck %s --check-prefixes=CHECK-O,CHECK-O1,CHECK-POSTLINK-O,%llvmcheckext
+; RUN:     | FileCheck %s --check-prefixes=CHECK-O,CHECK-O1,CHECK-POSTLINK-O,CHECK-POSTLINK-O1,%llvmcheckext
 ; RUN: opt -disable-verify -verify-cfg-preserved=0 -eagerly-invalidate-analyses=0 -debug-pass-manager \
 ; RUN:     -passes='thinlto<O2>' -S  %s 2>&1 \
 ; RUN:     | FileCheck %s --check-prefixes=CHECK-O,CHECK-O2,CHECK-O23SZ,CHECK-POSTLINK-O,%llvmcheckext,CHECK-POSTLINK-O2
@@ -221,6 +221,8 @@
 ; CHECK-POSTLINK-O-NEXT: Running pass: LoopVectorizePass
 ; CHECK-POSTLINK-O-NEXT: Running analysis: BlockFrequencyAnalysis
 ; CHECK-POSTLINK-O-NEXT: Running analysis: BranchProbabilityAnalysis
+; CHECK-POSTLINK-O1-NEXT: Running analysis: MemoryDependenceAnalysis
+; CHECK-POSTLINK-O1-NEXT: Running analysis: PhiValuesAnalysis
 ; CHECK-POSTLINK-O-NEXT: Running pass: LoopLoadEliminationPass
 ; CHECK-POSTLINK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-POSTLINK-O-NEXT: Running pass: SimplifyCFGPass
diff --git a/llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll b/llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll
--- a/llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll
@@ -177,6 +177,8 @@
 ; CHECK-O-NEXT: Running analysis: LoopAccessAnalysis on foo
 ; CHECK-O-NEXT: Running pass: InjectTLIMappings
 ; CHECK-O-NEXT: Running pass: LoopVectorizePass
+; CHECK-O1-NEXT: Running analysis: MemoryDependenceAnalysis
+; CHECK-O1-NEXT: Running analysis: PhiValuesAnalysis
 ; CHECK-O-NEXT: Running pass: LoopLoadEliminationPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
diff --git a/llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll b/llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll
--- a/llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll
@@ -189,6 +189,8 @@
 ; CHECK-O-NEXT: Running analysis: LoopAccessAnalysis
 ; CHECK-O-NEXT: Running pass: InjectTLIMappings
 ; CHECK-O-NEXT: Running pass: LoopVectorizePass
+; CHECK-O1-NEXT: Running analysis: MemoryDependenceAnalysis
+; CHECK-O1-NEXT: Running analysis: PhiValuesAnalysis
 ; CHECK-O-NEXT: Running pass: LoopLoadEliminationPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass