Fix handling of potential string additions in hydrogen.

src/hydrogen.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/hydrogen.h"
 
 #include <algorithm>
 
 #include "src/v8.h"
 
@@ skipping 10222 matching lines @@
     Type* right_type,
     Type* result_type,
     Maybe<int> fixed_right_arg,
     HAllocationMode allocation_mode) {
 
   Representation left_rep = Representation::FromType(left_type);
   Representation right_rep = Representation::FromType(right_type);
 
   bool maybe_string_add = op == Token::ADD &&
                           (left_type->Maybe(Type::String()) ||
-                           right_type->Maybe(Type::String()));
+                           left_type->Maybe(Type::Receiver()) ||
+                           right_type->Maybe(Type::String()) ||
+                           right_type->Maybe(Type::Receiver()));
 
   if (left_type->Is(Type::None())) {
     Add<HDeoptimize>("Insufficient type feedback for LHS of binary operation",
                      Deoptimizer::SOFT);
     // TODO(rossberg): we should be able to get rid of non-continuous
     // defaults.
     left_type = Type::Any(zone());
   } else {
     if (!maybe_string_add) left = TruncateToNumber(left, &left_type);
     left_rep = Representation::FromType(left_type);
@@ skipping 2223 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal