Index: include/llvm/Analysis/MemoryDependenceAnalysis.h
===================================================================
--- include/llvm/Analysis/MemoryDependenceAnalysis.h
+++ include/llvm/Analysis/MemoryDependenceAnalysis.h
@@ -350,6 +350,11 @@
                           DominatorTree &DT)
       : AA(AA), AC(AC), TLI(TLI), DT(DT) {}
 
+  /// Some methods limit the number of instructions they will examine.
+  /// The return value of this method is the default limit that will be
+  /// used if no limit is explicitly passed in.
+  unsigned getDefaultBlockScanLimit() const;
+
   /// Returns the instruction on which a memory operation depends.
   ///
   /// See the class comment for more details.  It is illegal to call this on
@@ -409,19 +414,25 @@
   /// operations.  If isLoad is false, this routine ignores may-aliases
   /// with reads from read-only locations. If possible, pass the query
   /// instruction as well; this function may take advantage of the metadata
-  /// annotated to the query instruction to refine the result.
+  /// annotated to the query instruction to refine the result. \p Limit
+  /// can be used to set the maximum number of instructions that will be
+  /// examined to find the pointer dependency. On return, it will be set to
+  /// the number of instructions left to examine. If a null pointer is passed
+  /// in, the limit will default to the value of -memdep-block-scan-limit.
   ///
   /// Note that this is an uncached query, and thus may be inefficient.
   MemDepResult getPointerDependencyFrom(const MemoryLocation &Loc, bool isLoad,
                                         BasicBlock::iterator ScanIt,
                                         BasicBlock *BB,
-                                        Instruction *QueryInst = nullptr);
+                                        Instruction *QueryInst = nullptr,
+                                        unsigned *Limit = nullptr);
 
   MemDepResult getSimplePointerDependencyFrom(const MemoryLocation &MemLoc,
                                               bool isLoad,
                                               BasicBlock::iterator ScanIt,
                                               BasicBlock *BB,
-                                              Instruction *QueryInst);
+                                              Instruction *QueryInst,
+                                              unsigned *Limit = nullptr);
 
   /// This analysis looks for other loads and stores with invariant.group
   /// metadata and the same pointer operand. Returns Unknown if it does not
Index: lib/Analysis/MemoryDependenceAnalysis.cpp
===================================================================
--- lib/Analysis/MemoryDependenceAnalysis.cpp
+++ lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -327,7 +327,7 @@
 
 MemDepResult MemoryDependenceResults::getPointerDependencyFrom(
     const MemoryLocation &MemLoc, bool isLoad, BasicBlock::iterator ScanIt,
-    BasicBlock *BB, Instruction *QueryInst) {
+    BasicBlock *BB, Instruction *QueryInst, unsigned *Limit) {
 
   if (QueryInst != nullptr) {
     if (auto *LI = dyn_cast<LoadInst>(QueryInst)) {
@@ -338,7 +338,8 @@
         return invariantGroupDependency;
     }
   }
-  return getSimplePointerDependencyFrom(MemLoc, isLoad, ScanIt, BB, QueryInst);
+  return getSimplePointerDependencyFrom(MemLoc, isLoad, ScanIt, BB, QueryInst,
+                                        Limit);
 }
 
 MemDepResult
@@ -394,13 +395,18 @@
 
 MemDepResult MemoryDependenceResults::getSimplePointerDependencyFrom(
     const MemoryLocation &MemLoc, bool isLoad, BasicBlock::iterator ScanIt,
-    BasicBlock *BB, Instruction *QueryInst) {
+    BasicBlock *BB, Instruction *QueryInst, unsigned *Limit) {
 
   const Value *MemLocBase = nullptr;
   int64_t MemLocOffset = 0;
-  unsigned Limit = BlockScanLimit;
   bool isInvariantLoad = false;
 
+  if (!Limit) {
+    unsigned DefaultLimit = BlockScanLimit;
+    return getSimplePointerDependencyFrom(MemLoc, isLoad, ScanIt, BB, QueryInst,
+                                          &DefaultLimit);
+  }
+
   // We must be careful with atomic accesses, as they may allow another thread
   //   to touch this location, clobbering it. We are conservative: if the
   //   QueryInst is not a simple (non-atomic) memory access, we automatically
@@ -474,8 +480,8 @@
 
     // Limit the amount of scanning we do so we don't end up with quadratic
     // running time on extreme testcases.
-    --Limit;
-    if (!Limit)
+    --*Limit;
+    if (!*Limit)
       return MemDepResult::getUnknown();
 
     if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
@@ -1698,6 +1704,10 @@
   AU.addRequiredTransitive<TargetLibraryInfoWrapperPass>();
 }
 
+unsigned MemoryDependenceResults::getDefaultBlockScanLimit() const {
+  return BlockScanLimit;
+}
+
 bool MemoryDependenceWrapperPass::runOnFunction(Function &F) {
   auto &AA = getAnalysis<AAResultsWrapperPass>().getAAResults();
   auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
Index: lib/Transforms/Scalar/DeadStoreElimination.cpp
===================================================================
--- lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -1051,6 +1051,13 @@
     if (!Loc.Ptr)
       continue;
 
+    // Loop until we find a store we can eliminate or a load that
+    // invalidates the analysis. Without an upper bound on the number of
+    // instructions examined, this analysis can become very time-consuming.
+    // However, the potential gain diminishes as we process more instructions
+    // without eliminating any of them. Therefore, we limit the number of
+    // instructions we look at.
+    auto Limit = MD->getDefaultBlockScanLimit();
     while (InstDep.isDef() || InstDep.isClobber()) {
       // Get the memory clobbered by the instruction we depend on.  MemDep will
       // skip any instructions that 'Loc' clearly doesn't interact with.  If we
@@ -1139,8 +1146,9 @@
       if (AA->getModRefInfo(DepWrite, Loc) & MRI_Ref)
         break;
 
-      InstDep = MD->getPointerDependencyFrom(Loc, false,
-                                             DepWrite->getIterator(), &BB);
+      InstDep = MD->getPointerDependencyFrom(Loc, /*isLoad=*/ false,
+                                             DepWrite->getIterator(), &BB,
+                                             /*QueryInst=*/ nullptr, &Limit);
     }
   }