Only fold polymorphic into monomorphic load if all load from either receiver or same prototype.

src/hydrogen.cc

 // Copyright 2013 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 4689 matching lines @@
 }
 
 
 bool HOptimizedGraphBuilder::PropertyAccessInfo::IsCompatibleForLoad(
     PropertyAccessInfo* info) {
   if (!CanInlinePropertyAccess(*map_)) return false;
 
   if (!LookupDescriptor()) return false;
 
   if (!lookup_.IsFound()) {
-    return (!info->lookup_.IsFound() || !info->holder_.is_null()) &&
+    return (!info->lookup_.IsFound() || info->has_holder()) &&
         map_->prototype() == info->map_->prototype();
   }
 
+  // Mismatch if the other access info found the property in the prototype
+  // chain.
+  if (info->has_holder()) return false;
+
   if (lookup_.IsPropertyCallbacks()) {
     return accessor_.is_identical_to(info->accessor_);
   }
 
   if (lookup_.IsConstant()) {
     return constant_.is_identical_to(info->constant_);
   }
 
   ASSERT(lookup_.IsField());
   if (!info->lookup_.IsField()) return false;
@@ skipping 5123 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal