[DSE] Only query object size for identified objects

This is supposed to be a fast heuristic primarily interested in
allocas. We should not call it for non-root objects where object
size needs to be determined recursively.

Author: nikic

llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

@@ -949,7 +949,8 @@ struct DSEState {
 
     // Check whether the killing store overwrites the whole object, in which
     // case the size/offset of the dead store does not matter.
-    if (DeadUndObj == KillingUndObj && KillingLocSize.isPrecise()) {
+    if (DeadUndObj == KillingUndObj && KillingLocSize.isPrecise() &&
+        isIdentifiedObject(KillingUndObj)) {
       uint64_t KillingUndObjSize = getPointerSize(KillingUndObj, DL, TLI, &F);
       if (KillingUndObjSize != MemoryLocation::UnknownSize &&
           KillingUndObjSize == KillingLocSize.getValue())