[AArch64] Add an assert to ensure we don't scale an offset that can't be scaled.

llvm-svn: 260272
diff --git a/llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp b/llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp
index f85d6a8..d07ef3c 100644
--- a/llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp
+++ b/llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp
@@ -842,8 +842,10 @@
   }
   int OffsetImm = getLdStOffsetOp(RtMI).getImm();
   // Handle Unscaled.
-  if (IsUnscaled)
+  if (IsUnscaled) {
+    assert (!(OffsetImm % OffsetStride) && "Unscaled offset cannot be scaled.");
     OffsetImm /= OffsetStride;
+  }
 
   // Construct the new instruction.
   MachineInstrBuilder MIB;