Introduce basic type feedback for for-in statements to avoid deopts.

src/hydrogen.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 3256 matching lines @@
 
 void HGraphBuilder::VisitForInStatement(ForInStatement* stmt) {
   ASSERT(!HasStackOverflow());
   ASSERT(current_block() != NULL);
   ASSERT(current_block()->HasPredecessor());
 
   if (!FLAG_optimize_for_in) {
     return Bailout("ForInStatement optimization is disabled");
   }
 
+  if (!oracle()->IsForInFastCase(stmt)) {
+    return Bailout("ForInStatement is not fast case");
+  }
+
   if (!stmt->each()->IsVariableProxy() ||
       !stmt->each()->AsVariableProxy()->var()->IsStackLocal()) {
     return Bailout("ForInStatement with non-local each variable");
   }
 
   Variable* each_var = stmt->each()->AsVariableProxy()->var();
 
   CHECK_ALIVE(VisitForValue(stmt->enumerable()));
   HValue* enumerable = Top();  // Leave enumerable at the top.
 
@@ skipping 4751 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify(false);  // No full verify.
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal