[strong] Disallow implicit conversions for add

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 <sstream>
 
 #include "src/v8.h"
 
@@ skipping 10593 matching lines @@
     if (left_type->Is(Type::String())) {
       left = BuildCheckString(left);
     }
 
     // Validate type feedback for right argument.
     if (right_type->Is(Type::String())) {
       right = BuildCheckString(right);
     }
 
     // Convert left argument as necessary.
-    if (left_type->Is(Type::Number())) {
+    if (left_type->Is(Type::Number()) && !is_strong(language_mode)) {
       DCHECK(right_type->Is(Type::String()));
       left = BuildNumberToString(left, left_type);
     } else if (!left_type->Is(Type::String())) {
       DCHECK(right_type->Is(Type::String()));
-      HValue* function = AddLoadJSBuiltin(Builtins::STRING_ADD_RIGHT);
+      HValue* function = AddLoadJSBuiltin(is_strong(language_mode) ?
+                                            Builtins::STRING_ADD_RIGHT_STRONG :
+                                            Builtins::STRING_ADD_RIGHT);
       Add<HPushArguments>(left, right);
       return AddUncasted<HInvokeFunction>(function, 2);
     }
 
     // Convert right argument as necessary.
-    if (right_type->Is(Type::Number())) {
+    if (right_type->Is(Type::Number()) && !is_strong(language_mode)) {
       DCHECK(left_type->Is(Type::String()));
       right = BuildNumberToString(right, right_type);
     } else if (!right_type->Is(Type::String())) {
       DCHECK(left_type->Is(Type::String()));
-      HValue* function = AddLoadJSBuiltin(Builtins::STRING_ADD_LEFT);
+      HValue* function = AddLoadJSBuiltin(is_strong(language_mode) ?
+                                            Builtins::STRING_ADD_LEFT_STRONG :
+                                            Builtins::STRING_ADD_LEFT);
       Add<HPushArguments>(left, right);
       return AddUncasted<HInvokeFunction>(function, 2);
     }
 
     // Fast paths for empty constant strings.
     Handle<String> left_string =
         left->IsConstant() && HConstant::cast(left)->HasStringValue()
             ? HConstant::cast(left)->StringValue()
             : Handle<String>();
     Handle<String> right_string =
@@ skipping 2465 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal