Propagate class ids using existing type propagation framework.

runtime/vm/flow_graph_optimizer.cc

Index: runtime/vm/flow_graph_optimizer.cc
===================================================================
--- runtime/vm/flow_graph_optimizer.cc	(revision 10775)
+++ runtime/vm/flow_graph_optimizer.cc	(working copy)
@@ -661,6 +661,12 @@
 }
 
 
+// TODO(srdjan): Investigate if the propagated cid should be more specific.
+void FlowGraphTypePropagator::VisitPushArgument(PushArgumentInstr* push) {
+  if (!push->has_propagated_cid()) push->SetPropagatedCid(kDynamicCid);
+}
+
+
 void FlowGraphTypePropagator::VisitBind(BindInstr* bind) {
   // No need to propagate the input types of the bound computation, as long as
   // PhiInstr's are handled as part of JoinEntryInstr.
@@ -672,6 +678,12 @@
   if (changed) {
     still_changing_ = true;
   }
+  // Propagate class ids.
+  intptr_t cid = bind->computation()->ResultCid();
+  changed = bind->SetPropagatedCid(cid);
+  if (changed) {
+    still_changing_ = true;
+  }
 }
 
 
@@ -686,6 +698,32 @@
   if (changed) {
     still_changing_ = true;
   }
+
+  // Merge class ids: if any two inputs have different class ids then result
+  // is kDynamicCid.
+  intptr_t merged_cid = kIllegalCid;
+  for (intptr_t i = 0; i < phi->InputCount(); i++) {
+    // Result cid of UseVal can be kIllegalCid if the referred definition
+    // has not been visited yet.
+    intptr_t cid = phi->InputAt(i)->ResultCid();
+    if (cid == kIllegalCid) {
+      still_changing_ = true;
+      continue;
+    }
+    if (merged_cid == kIllegalCid) {
+      // First time set.
+      merged_cid = cid;
+    } else if (merged_cid != cid) {
+      merged_cid = kDynamicCid;
+    }
+  }
+  if (merged_cid == kIllegalCid) {
+    merged_cid = kDynamicCid;
+  }
+  changed = phi->SetPropagatedCid(merged_cid);
+  if (changed) {
+    still_changing_ = true;
+  }
 }