diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -144,6 +144,24 @@
   return TheStores.size() > NumPointerStores+NumByteStores;
 }
 
+
+static Align findStoreAlignment(const DataLayout &DL, const StoreInst *SI) {
+  return DL.getValueOrABITypeAlignment(MaybeAlign(SI->getAlignment()),
+                                       SI->getOperand(0)->getType());
+}
+
+static Align findLoadAlignment(const DataLayout &DL, const LoadInst *LI) {
+  return DL.getValueOrABITypeAlignment(MaybeAlign(LI->getAlignment()),
+                                       LI->getType());
+}
+
+static Align findCommonAlignment(const DataLayout &DL, const StoreInst *SI,
+                                 const LoadInst *LI) {
+  Align StoreAlign = findStoreAlignment(DL, SI);
+  Align LoadAlign = findLoadAlignment(DL, LI);
+  return commonAlignment(StoreAlign, LoadAlign);
+}
+
 namespace {
 
 class MemsetRanges {
@@ -173,8 +191,8 @@
   void addStore(int64_t OffsetFromFirst, StoreInst *SI) {
     int64_t StoreSize = DL.getTypeStoreSize(SI->getOperand(0)->getType());
 
-    addRange(OffsetFromFirst, StoreSize,
-             SI->getPointerOperand(), SI->getAlignment(), SI);
+    addRange(OffsetFromFirst, StoreSize, SI->getPointerOperand(),
+             findStoreAlignment(DL, SI).value(), SI);
   }
 
   void addMemSet(int64_t OffsetFromFirst, MemSetInst *MSI) {
@@ -387,13 +405,8 @@
     // Get the starting pointer of the block.
     StartPtr = Range.StartPtr;
 
-    // Determine alignment
-    const Align Alignment = DL.getValueOrABITypeAlignment(
-        MaybeAlign(Range.Alignment),
-        cast<PointerType>(StartPtr->getType())->getElementType());
-
     AMemSet = Builder.CreateMemSet(StartPtr, ByteVal, Range.End - Range.Start,
-                                   Alignment);
+                                   MaybeAlign(Range.Alignment));
     LLVM_DEBUG(dbgs() << "Replace stores:\n"; for (Instruction *SI
                                                    : Range.TheStores) dbgs()
                                               << *SI << '\n';
@@ -413,23 +426,6 @@
   return AMemSet;
 }
 
-static Align findStoreAlignment(const DataLayout &DL, const StoreInst *SI) {
-  return DL.getValueOrABITypeAlignment(MaybeAlign(SI->getAlignment()),
-                                       SI->getOperand(0)->getType());
-}
-
-static Align findLoadAlignment(const DataLayout &DL, const LoadInst *LI) {
-  return DL.getValueOrABITypeAlignment(MaybeAlign(LI->getAlignment()),
-                                       LI->getType());
-}
-
-static Align findCommonAlignment(const DataLayout &DL, const StoreInst *SI,
-                                 const LoadInst *LI) {
-  Align StoreAlign = findStoreAlignment(DL, SI);
-  Align LoadAlign = findLoadAlignment(DL, LI);
-  return commonAlignment(StoreAlign, LoadAlign);
-}
-
 // This method try to lift a store instruction before position P.
 // It will lift the store and its argument + that anything that
 // may alias with these.
diff --git a/llvm/test/Transforms/MemCpyOpt/form-memset.ll b/llvm/test/Transforms/MemCpyOpt/form-memset.ll
--- a/llvm/test/Transforms/MemCpyOpt/form-memset.ll
+++ b/llvm/test/Transforms/MemCpyOpt/form-memset.ll
@@ -217,7 +217,7 @@
   tail call void @llvm.memset.p0i8.i64(i8* %1, i8 0, i64 12, i1 false)
   ret void
 ; CHECK-LABEL: @test6(
-; CHECK: call void @llvm.memset.p0i8.i64(i8* align 4 %2, i8 0, i64 24, i1 false)
+; CHECK: call void @llvm.memset.p0i8.i64(i8* %2, i8 0, i64 24, i1 false)
 }
 
 ; More aggressive heuristic
@@ -280,7 +280,7 @@
   ret void
 ; CHECK-LABEL: @test10(
 ; CHECK-NOT: memset
-; CHECK: call void @llvm.memset.p0i8.i64(i8* align 1 %P, i8 0, i64 42, i1 false)
+; CHECK: call void @llvm.memset.p0i8.i64(i8* %P, i8 0, i64 42, i1 false)
 ; CHECK-NOT: memset
 ; CHECK: ret void
 }
@@ -299,3 +299,16 @@
 ; CHECK-NOT: store
 ; CHECK: call void @llvm.memset.p0i8.i64(i8* align 4 %1, i8 1, i64 23, i1 false)
 }
+
+; Alignment should be preserved when there is a store with default align
+define void @test12(i32* nocapture %P) nounwind ssp {
+entry:
+  store i32 0, i32* %P
+  %add.ptr = getelementptr inbounds i32, i32* %P, i64 1
+  %0 = bitcast i32* %add.ptr to i8*
+  tail call void @llvm.memset.p0i8.i64(i8* %0, i8 0, i64 11, i1 false)
+  ret void
+; CHECK-LABEL: @test12(
+; CHECK-NOT: store
+; CHECK: call void @llvm.memset.p0i8.i64(i8* align 4 %1, i8 0, i64 15, i1 false)
+}