diff --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
--- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -87,6 +87,8 @@
 STATISTIC(NumCFGChecks, "Number of stores modified");
 STATISTIC(NumCFGTries, "Number of stores modified");
 STATISTIC(NumCFGSuccess, "Number of stores modified");
+STATISTIC(NumDomMemDefChecks,
+          "Number iterations check for reads in getDomMemoryDef");
 
 DEBUG_COUNTER(MemorySSACounter, "dse-memoryssa",
               "Controls which MemoryDefs are eliminated.");
@@ -1543,6 +1545,18 @@
   /// basic block.
   DenseMap<BasicBlock *, InstOverlapIntervalsTy> IOLs;
 
+  struct CheckCache {
+    SmallPtrSet<MemoryAccess *, 16> KnownNoReads;
+    SmallPtrSet<MemoryAccess *, 16> KnownReads;
+
+    bool isKnownNoRead(MemoryAccess *A) const {
+      return KnownNoReads.find(A) != KnownNoReads.end();
+    }
+    bool isKnownRead(MemoryAccess *A) const {
+      return KnownReads.find(A) != KnownReads.end();
+    }
+  };
+
   DSEState(Function &F, AliasAnalysis &AA, MemorySSA &MSSA, DominatorTree &DT,
            PostDominatorTree &PDT, const TargetLibraryInfo &TLI)
       : F(F), AA(AA), BatchAA(AA), MSSA(MSSA), DT(DT), PDT(PDT), TLI(TLI),
@@ -1797,17 +1811,17 @@
   // MemoryDef, return None. The returned value may not (completely) overwrite
   // \p DefLoc. Currently we bail out when we encounter an aliasing MemoryUse
   // (read).
-  Optional<MemoryAccess *> getDomMemoryDef(MemoryDef *KillingDef,
-                                           MemoryAccess *Current,
-                                           MemoryLocation DefLoc,
-                                           const Value *DefUO,
-                                           unsigned &ScanLimit) {
+  Optional<MemoryAccess *>
+  getDomMemoryDef(MemoryDef *KillingDef, MemoryAccess *Current,
+                  MemoryLocation DefLoc, const Value *DefUO, CheckCache &Cache,
+                  unsigned &ScanLimit) {
     if (ScanLimit == 0) {
       LLVM_DEBUG(dbgs() << "\n    ...  hit scan limit\n");
       return None;
     }
 
     MemoryAccess *DomAccess;
+    MemoryAccess *StartAccess = Current;
     bool StepAgain;
     LLVM_DEBUG(dbgs() << "  trying to get dominating access for " << *Current
                       << "\n");
@@ -1847,10 +1861,13 @@
     // they cover all paths from DomAccess to any function exit.
     SmallPtrSet<Instruction *, 16> KillingDefs;
     KillingDefs.insert(KillingDef->getMemoryInst());
+    Instruction *DomMemInst = isa<MemoryDef>(DomAccess)
+                                  ? cast<MemoryDef>(DomAccess)->getMemoryInst()
+                                  : nullptr;
     LLVM_DEBUG({
       dbgs() << "  Checking for reads of " << *DomAccess;
-      if (isa<MemoryDef>(DomAccess))
-        dbgs() << " (" << *cast<MemoryDef>(DomAccess)->getMemoryInst() << ")\n";
+      if (DomMemInst)
+        dbgs() << " (" << *DomMemInst << ")\n";
       else
         dbgs() << ")\n";
     });
@@ -1862,6 +1879,11 @@
     };
     PushMemUses(DomAccess);
 
+    // Optimistically collect all accesses we for reads. If we do not find any
+    // read clobbers, add them to the cache.
+    SmallPtrSet<MemoryAccess *, 16> KnownNoReads;
+    if (!DomMemInst || !DomMemInst->mayReadFromMemory())
+      KnownNoReads.insert(DomAccess);
     // Check if DomDef may be read.
     for (unsigned I = 0; I < WorkList.size(); I++) {
       MemoryAccess *UseAccess = WorkList[I];
@@ -1873,6 +1895,20 @@
         return None;
       }
       --ScanLimit;
+      NumDomMemDefChecks++;
+
+      // Check if we already visited this access.
+      if (Cache.isKnownNoRead(UseAccess)) {
+        LLVM_DEBUG(dbgs() << " ... skip, discovered that " << *UseAccess
+                          << " is safe earlier.\n");
+        continue;
+      }
+      if (Cache.isKnownRead(UseAccess)) {
+        LLVM_DEBUG(dbgs() << " ... bail out, discovered that " << *UseAccess
+                          << " is has a read-clobber earlier.\n");
+        return None;
+      }
+      KnownNoReads.insert(UseAccess);
 
       if (isa<MemoryPhi>(UseAccess)) {
         if (any_of(KillingDefs, [this, UseAccess](Instruction *KI) {
@@ -1912,6 +1948,9 @@
       // original MD. Stop walk.
       if (isReadClobber(DefLoc, UseInst)) {
         LLVM_DEBUG(dbgs() << "    ... found read clobber\n");
+        Cache.KnownReads.insert(UseAccess);
+        Cache.KnownReads.insert(StartAccess);
+        Cache.KnownReads.insert(DomAccess);
         return None;
       }
 
@@ -2028,6 +2067,7 @@
       return None;
     }
 
+    Cache.KnownNoReads.insert(KnownNoReads.begin(), KnownNoReads.end());
     // No aliasing MemoryUses of DomAccess found, DomAccess is potentially dead.
     return {DomAccess};
   }
@@ -2235,6 +2275,7 @@
     ToCheck.insert(KillingDef->getDefiningAccess());
 
     //State.PointerMayBeCapturedBeforeCache.clear();
+    DSEState::CheckCache Cache;
     // Check if MemoryAccesses in the worklist are killed by KillingDef.
     for (unsigned I = 0; I < ToCheck.size(); I++) {
       Current = ToCheck[I];
@@ -2242,7 +2283,7 @@
         continue;
 
       Optional<MemoryAccess *> Next = State.getDomMemoryDef(
-          KillingDef, Current, SILoc, SILocUnd, ScanLimit);
+          KillingDef, Current, SILoc, SILocUnd, Cache, ScanLimit);
 
       if (!Next) {
         LLVM_DEBUG(dbgs() << "  finished walk\n");