Index: lib/Target/ARM/ARMLoadStoreOptimizer.cpp
===================================================================
--- lib/Target/ARM/ARMLoadStoreOptimizer.cpp
+++ lib/Target/ARM/ARMLoadStoreOptimizer.cpp
@@ -1575,6 +1575,36 @@
   if (MMO.getAlignment() < 4)
     return false;
 
+  // Check that the pointer has not been cast up to a larger type, as this
+  // could create an unaligned access.
+  std::function<bool(const Value*)> IsAlignedPtr = [&](const Value *Ptr) {
+    auto *PtrTy = cast<PointerType>(Ptr->getType());
+    unsigned AccessSize = PtrTy->getElementType()->getScalarSizeInBits();
+    if (auto *Cast = dyn_cast<BitCastInst>(Ptr)) {
+      if (auto *CastedPtrTy = dyn_cast<PointerType>(Cast->getSrcTy())) {
+        unsigned MemSize = CastedPtrTy->getElementType()->getScalarSizeInBits();
+        if (isa<PointerType>(CastedPtrTy->getElementType()))
+          return IsAlignedPtr(Cast->getOperand(0));
+        else
+          return AccessSize <= MemSize;
+      }
+    }
+    return true;
+  };
+
+  // Ensure that the underlying memory is truly aligned. This ensures that we
+  // don't create create illegal accesses when the DSP instructions use LDR
+  // and STR to load and store packed data.
+  const MachinePointerInfo &PointerInfo = MMO.getPointerInfo();
+  if (!PointerInfo.V.isNull() && PointerInfo.V.is<const Value*>()) {
+    auto *PtrVal = PointerInfo.V.get<const Value*>();
+    if (auto *GEP = dyn_cast<GetElementPtrInst>(PtrVal)) {
+      if (!IsAlignedPtr(GEP->getPointerOperand()))
+        return false;
+    } else if (isa<BitCastInst>(PtrVal) && !IsAlignedPtr(PtrVal))
+      return false;
+  }
+
   // str <undef> could probably be eliminated entirely, but for now we just want
   // to avoid making a mess of it.
   // FIXME: Use str <undef> as a wildcard to enable better stm folding.
Index: test/CodeGen/ARM/ldrd-strd-unaligned.ll
===================================================================
--- /dev/null
+++ test/CodeGen/ARM/ldrd-strd-unaligned.ll
@@ -0,0 +1,55 @@
+; RUN: llc -mtriple=thumbv7em -mcpu=cortex-m7 %s -o - | FileCheck %s
+; RUN: llc -mtriple=thumbv7 -mcpu=cortex-a8 %s -o - | FileCheck %s
+; RUN: llc -mtriple=thumbv8 -mcpu=cortex-a53 %s -o - | FileCheck %s
+
+; CHECK-LABEL: bitcast_ptr_ldr
+; CHECK-NOT: ldrd
+define i32 @bitcast_ptr_ldr(i16* %In) {
+entry:
+  %0 = bitcast i16* %In to i32*
+  %in.addr.0 = getelementptr inbounds i32, i32* %0, i32 0
+  %in.addr.1 = getelementptr inbounds i32, i32* %0, i32 1
+  %1 = load i32, i32* %in.addr.0, align 4
+  %2 = load i32, i32* %in.addr.1, align 4
+  %mul = mul i32 %1, %2
+  ret i32 %mul
+}
+
+; CHECK-LABEL: bitcast_gep_ldr
+; CHECK-NOT: ldrd
+define i32 @bitcast_gep_ldr(i16* %In) {
+entry:
+  %in.addr.0 = getelementptr inbounds i16, i16* %In, i32 0
+  %in.addr.1 = getelementptr inbounds i16, i16* %In, i32 2
+  %cast.0 = bitcast i16* %in.addr.0 to i32*
+  %cast.1 = bitcast i16* %in.addr.1 to i32*
+  %0 = load i32, i32* %cast.0, align 4
+  %1 = load i32, i32* %cast.1, align 4
+  %mul = mul i32 %0, %1
+  ret i32 %mul
+}
+
+; CHECK-LABEL: bitcast_ptr_str
+; CHECK-NOT: strd
+define void @bitcast_ptr_str(i32 %arg0, i32 %arg1, i16* %out) {
+entry:
+  %0 = bitcast i16* %out to i32*
+  %out.addr.0 = getelementptr inbounds i32, i32* %0, i32 0
+  %out.addr.1 = getelementptr inbounds i32, i32* %0, i32 1
+  store i32 %arg0, i32* %out.addr.0, align 4
+  store i32 %arg1, i32* %out.addr.1, align 4
+  ret void
+}
+
+; CHECK-LABEL: bitcast_gep_str
+; CHECK-NOT: strd
+define void @bitcast_gep_str(i32 %arg0, i32 %arg1, i16* %out) {
+entry:
+  %out.addr.0 = getelementptr inbounds i16, i16* %out, i32 0
+  %out.addr.1 = getelementptr inbounds i16, i16* %out, i32 2
+  %cast.0 = bitcast i16* %out.addr.0 to i32*
+  %cast.1 = bitcast i16* %out.addr.1 to i32*
+  store i32 %arg0, i32* %cast.0, align 4
+  store i32 %arg1, i32* %cast.1, align 4
+  ret void
+}