Index: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -8110,6 +8110,19 @@
         Store->isIndexed())
       return SDValue();
     Stores.push_back(Store);
+
+    // If this store is used as a chain operand in a store that is not included
+    // in the set of stores to be merged, then the transform may not be safe.
+    // We must preserve the order of that other store relative to the indivdual
+    // stores in this set.
+    for (SDNode *Use : Store->uses()) {
+      auto *StoreUse = dyn_cast<StoreSDNode>(Use);
+      if (StoreUse && StoreUse->getChain().getNode() == Store &&
+          !is_contained(Stores, StoreUse))
+        return SDValue();
+    }
+
+    // Get the next link in the chain and try to collect another store.
     Chain = Store->getChain();
   }
   // There is no reason to continue if we do not have at least a pair of stores.
Index: llvm/test/CodeGen/SystemZ/merge-stores.ll
===================================================================
--- llvm/test/CodeGen/SystemZ/merge-stores.ll
+++ llvm/test/CodeGen/SystemZ/merge-stores.ll
@@ -16,8 +16,8 @@
 ; CHECK-NEXT:    srlg %r0, %r2, 32
 ; CHECK-NEXT:    st %r0, 0(%r1)
 ; CHECK-NEXT:    lhi %r0, 0
-; CHECK-NEXT:    stg %r2, 0(%r1)
 ; CHECK-NEXT:    sthrl %r0, e
+; CHECK-NEXT:    st %r2, 4(%r1)
 ; CHECK-NEXT:    strl %r2, d
 ; CHECK-NEXT:    br %r14
   %xsh = lshr i64 %x, 32