Index: lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- lib/Transforms/Vectorize/LoopVectorize.cpp
+++ lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -4268,57 +4268,66 @@
       bool UseDeferred = SetIteration > 0;
       PtrAccessSet &S = UseDeferred ? DeferredAccesses : Accesses;
 
-      for (auto A : AS) {
-        Value *Ptr = A.getValue();
-        bool IsWrite = S.count(MemAccessInfo(Ptr, true));
+      for (auto AV : AS) {
+        Value *Ptr = AV.getValue();
 
-        // If we're using the deferred access set, then it contains only reads.
-        bool IsReadOnlyPtr = ReadOnlyPtr.count(Ptr) && !IsWrite;
-        if (UseDeferred && !IsReadOnlyPtr)
-          continue;
-        // Otherwise, the pointer must be in the PtrAccessSet, either as a read
-        // or a write.
-        assert(((IsReadOnlyPtr && UseDeferred) || IsWrite ||
-                 S.count(MemAccessInfo(Ptr, false))) &&
-               "Alias-set pointer not in the access set?");
-
-        MemAccessInfo Access(Ptr, IsWrite);
-        DepCands.insert(Access);
-
-        // Memorize read-only pointers for later processing and skip them in the
-        // first round (they need to be checked after we have seen all write
-        // pointers). Note: we also mark pointer that are not consecutive as
-        // "read-only" pointers (so that we check "a[b[i]] +="). Hence, we need
-        // the second check for "!IsWrite".
-        if (!UseDeferred && IsReadOnlyPtr) {
-          DeferredAccesses.insert(Access);
-          continue;
-        }
+        // For a single memory access in AliasSetTracker, Accesses may contain
+        // both read and write, and they both need to be handled for CheckDeps.
+        for (auto AC : S) {
+          if (AC.getPointer() != Ptr)
+            continue;
 
-        // If this is a write - check other reads and writes for conflicts.  If
-        // this is a read only check other writes for conflicts (but only if
-        // there is no other write to the ptr - this is an optimization to
-        // catch "a[i] = a[i] + " without having to do a dependence check).
-        if ((IsWrite || IsReadOnlyPtr) && SetHasWrite) {
-          CheckDeps.insert(Access);
-          IsRTCheckNeeded = true;
-        }
+          bool IsWrite = AC.getInt();
+
+          // If we're using the deferred access set, then it contains only
+          // reads.
+          bool IsReadOnlyPtr = ReadOnlyPtr.count(Ptr) && !IsWrite;
+          if (UseDeferred && !IsReadOnlyPtr)
+            continue;
+          // Otherwise, the pointer must be in the PtrAccessSet, either as a
+          // read or a write.
+          assert(((IsReadOnlyPtr && UseDeferred) || IsWrite ||
+                  S.count(MemAccessInfo(Ptr, false))) &&
+                 "Alias-set pointer not in the access set?");
+
+          MemAccessInfo Access(Ptr, IsWrite);
+          DepCands.insert(Access);
+
+          // Memorize read-only pointers for later processing and skip them in
+          // the first round (they need to be checked after we have seen all
+          // write pointers). Note: we also mark pointer that are not
+          // consecutive as "read-only" pointers (so that we check
+          // "a[b[i]] +="). Hence, we need the second check for "!IsWrite".
+          if (!UseDeferred && IsReadOnlyPtr) {
+            DeferredAccesses.insert(Access);
+            continue;
+          }
 
-        if (IsWrite)
-          SetHasWrite = true;
-
-        // Create sets of pointers connected by a shared alias set and
-        // underlying object.
-        typedef SmallVector<Value *, 16> ValueVector;
-        ValueVector TempObjects;
-        GetUnderlyingObjects(Ptr, TempObjects, DL);
-        for (Value *UnderlyingObj : TempObjects) {
-          UnderlyingObjToAccessMap::iterator Prev =
-            ObjToLastAccess.find(UnderlyingObj);
-          if (Prev != ObjToLastAccess.end())
-            DepCands.unionSets(Access, Prev->second);
-
-          ObjToLastAccess[UnderlyingObj] = Access;
+          // If this is a write - check other reads and writes for conflicts. If
+          // this is a read only check other writes for conflicts (but only if
+          // there is no other write to the ptr - this is an optimization to
+          // catch "a[i] = a[i] + " without having to do a dependence check).
+          if ((IsWrite || IsReadOnlyPtr) && SetHasWrite) {
+            CheckDeps.insert(Access);
+            IsRTCheckNeeded = true;
+          }
+
+          if (IsWrite)
+            SetHasWrite = true;
+
+          // Create sets of pointers connected by a shared alias set and
+          // underlying object.
+          typedef SmallVector<Value *, 16> ValueVector;
+          ValueVector TempObjects;
+          GetUnderlyingObjects(Ptr, TempObjects, DL);
+          for (Value *UnderlyingObj : TempObjects) {
+            UnderlyingObjToAccessMap::iterator Prev =
+                ObjToLastAccess.find(UnderlyingObj);
+            if (Prev != ObjToLastAccess.end())
+              DepCands.unionSets(Access, Prev->second);
+
+            ObjToLastAccess[UnderlyingObj] = Access;
+          }
         }
       }
     }
Index: test/Transforms/LoopVectorize/loop-vect-memdep.ll
===================================================================
--- /dev/null
+++ test/Transforms/LoopVectorize/loop-vect-memdep.ll
@@ -0,0 +1,26 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+; RUN: opt < %s -S -loop-vectorize -debug-only=loop-vectorize 2>&1 | FileCheck %s
+
+; CHECK: LV: Can't vectorize due to memory conflicts
+
+define void @test_loop_novect(double** %arr, i64 %n) {
+for.body.lr.ph:
+  %t = load double** %arr, align 8
+  br label %for.body
+
+for.body:                                      ; preds = %for.body, %for.body.lr.ph
+  %i = phi i64 [ 0, %for.body.lr.ph ], [ %i.next, %for.body ]
+  %a = getelementptr inbounds double* %t, i64 %i
+  %i.next = add nuw nsw i64 %i, 1
+  %a.next = getelementptr inbounds double* %t, i64 %i.next
+  %t1 = load double* %a, align 8
+  %t2 = load double* %a.next, align 8
+  store double %t1, double* %a.next, align 8
+  store double %t2, double* %a, align 8
+  %c = icmp eq i64 %i, %n
+  br i1 %c, label %final, label %for.body
+
+final:                                   ; preds = %for.body
+  ret void
+}