Index: lib/Analysis/MemoryDependenceAnalysis.cpp
===================================================================
--- lib/Analysis/MemoryDependenceAnalysis.cpp
+++ lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -1124,21 +1124,15 @@
   // If we already have a cache entry for this CacheKey, we may need to do some
   // work to reconcile the cache entry and the current query.
   if (!Pair.second) {
-    if (CacheInfo->Size < Loc.Size) {
-      // The query's Size is greater than the cached one. Throw out the
-      // cached data and proceed with the query at the greater size.
+    if (CacheInfo->Size != Loc.Size) {
+      // The query's Size differs from the cached one. Throw out the
+      // cached data and proceed with the query at the new size.
       CacheInfo->Pair = BBSkipFirstBlockPair();
       CacheInfo->Size = Loc.Size;
       for (auto &Entry : CacheInfo->NonLocalDeps)
         if (Instruction *Inst = Entry.getResult().getInst())
           RemoveFromReverseMap(ReverseNonLocalPtrDeps, Inst, CacheKey);
       CacheInfo->NonLocalDeps.clear();
-    } else if (CacheInfo->Size > Loc.Size) {
-      // This query's Size is less than the cached one. Conservatively restart
-      // the query using the greater size.
-      return getNonLocalPointerDepFromBB(
-          QueryInst, Pointer, Loc.getWithNewSize(CacheInfo->Size), isLoad,
-          StartBB, Result, Visited, SkipFirstBlock);
     }
 
     // If the query's AATags are inconsistent with the cached one,
Index: lib/Transforms/Scalar/MemCpyOptimizer.cpp
===================================================================
--- lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -476,22 +476,28 @@
       Alignment = DL.getABITypeAlignment(EltType);
     }
 
-    AMemSet =
-      Builder.CreateMemSet(StartPtr, ByteVal, Range.End-Range.Start, Alignment);
-
     DEBUG(dbgs() << "Replace stores:\n";
           for (Instruction *SI : Range.TheStores)
-            dbgs() << *SI << '\n';
-          dbgs() << "With: " << *AMemSet << '\n');
-
-    if (!Range.TheStores.empty())
-      AMemSet->setDebugLoc(Range.TheStores[0]->getDebugLoc());
+            dbgs() << *SI << '\n');
 
     // Zap all the stores.
     for (Instruction *SI : Range.TheStores) {
       MD->removeInstruction(SI);
       SI->eraseFromParent();
     }
+
+    // Create the memset after removing the stores, so that if there any cached
+    // non-local dependencies on the removed instructions, the cache entries
+    // are updated to "dirty" entries pointing below the memset, so subsequent
+    // queries include the memset.
+    AMemSet =
+      Builder.CreateMemSet(StartPtr, ByteVal, Range.End-Range.Start, Alignment);
+
+    DEBUG(dbgs() << "With: " << *AMemSet << '\n');
+
+    if (!Range.TheStores.empty())
+      AMemSet->setDebugLoc(Range.TheStores[0]->getDebugLoc());
+
     ++NumMemSetInfer;
   }
 
Index: test/Transforms/MemCpyOpt/mixed-sizes.ll
===================================================================
--- test/Transforms/MemCpyOpt/mixed-sizes.ll
+++ test/Transforms/MemCpyOpt/mixed-sizes.ll
@@ -0,0 +1,36 @@
+; RUN: opt < %s -memcpyopt -S | FileCheck %s
+; Handle memcpy-memcpy dependencies of differing sizes correctly.
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+; Don't delete the second memcpy, even though there's an earlier
+; memcpy with a larger size from the same address.
+
+; CHECK-LABEL: @foo
+define i32 @foo(i1 %z) {
+entry:
+  %a = alloca [10 x i32]
+  %s = alloca [10 x i32]
+  %0 = bitcast [10 x i32]* %a to i8*
+  %1 = bitcast [10 x i32]* %s to i8*
+  call void @llvm.memset.p0i8.i64(i8* nonnull %1, i8 0, i64 40, i32 16, i1 false)
+  %arrayidx = getelementptr inbounds [10 x i32], [10 x i32]* %a, i64 0, i64 0
+  store i32 1, i32* %arrayidx
+  %scevgep = getelementptr [10 x i32], [10 x i32]* %s, i64 0, i64 1
+  %scevgep7 = bitcast i32* %scevgep to i8*
+  br i1 %z, label %for.body3.lr.ph, label %for.inc7.1
+
+for.body3.lr.ph:                                  ; preds = %entry
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %0, i8* %scevgep7, i64 17179869180, i32 4, i1 false)
+  br label %for.inc7.1
+
+for.inc7.1:
+; CHECK: for.inc7.1:
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %0, i8* %scevgep7, i64 4, i32 4, i1 false)
+; CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %0, i8* %scevgep7, i64 4, i32 4, i1 false)
+  %2 = load i32, i32* %arrayidx
+  ret i32 %2
+}
+
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8*, i8*, i64, i32, i1)
+declare void @llvm.memset.p0i8.i64(i8*, i8, i64, i32, i1)