Support string add in crankshaft:

src/x64/code-stubs-x64.cc

 // Copyright 2011 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 354 matching lines @@
       UNREACHABLE();
       // The int32 case is identical to the Smi case.  We avoid creating this
       // ic state on x64.
       break;
     case TRBinaryOpIC::HEAP_NUMBER:
       GenerateHeapNumberStub(masm);
       break;
     case TRBinaryOpIC::ODDBALL:
       GenerateOddballStub(masm);
       break;
+    case TRBinaryOpIC::BOTH_STRING:
+      GenerateBothStringStub(masm);
+      break;
     case TRBinaryOpIC::STRING:
       GenerateStringStub(masm);
       break;
     case TRBinaryOpIC::GENERIC:
       GenerateGeneric(masm);
       break;
     default:
       UNREACHABLE();
   }
 }
@@ skipping 379 matching lines @@
 void TypeRecordingBinaryOpStub::GenerateStringStub(MacroAssembler* masm) {
   ASSERT(operands_type_ == TRBinaryOpIC::STRING);
   ASSERT(op_ == Token::ADD);
   GenerateStringAddCode(masm);
   // Try to add arguments as strings, otherwise, transition to the generic
   // TRBinaryOpIC type.
   GenerateTypeTransition(masm);
 }
 
 
+void TypeRecordingBinaryOpStub::GenerateBothStringStub(MacroAssembler* masm) {
+  Label call_runtime;
+  ASSERT(operands_type_ == TRBinaryOpIC::BOTH_STRING);
+  ASSERT(op_ == Token::ADD);
+  // If both arguments are strings, call the string add stub.
+  // Otherwise, do a transition.
+
+  // Registers containing left and right operands respectively.
+  Register left = rdx;
+  Register right = rax;
+
+  // Test if left operand is a string.
+  __ JumpIfSmi(left, &call_runtime);
+  __ CmpObjectType(left, FIRST_NONSTRING_TYPE, rcx);
+  __ j(above_equal, &call_runtime);
+
+  // Test if right operand is a string.
+  __ JumpIfSmi(right, &call_runtime);
+  __ CmpObjectType(right, FIRST_NONSTRING_TYPE, rcx);
+  __ j(above_equal, &call_runtime);
+
+  StringAddStub string_add_stub(NO_STRING_CHECK_IN_STUB);
+  GenerateRegisterArgsPush(masm);
+  __ TailCallStub(&string_add_stub);
+
+  __ bind(&call_runtime);
+  GenerateTypeTransition(masm);
+}
+
+
 void TypeRecordingBinaryOpStub::GenerateOddballStub(MacroAssembler* masm) {
   Label call_runtime;
 
   if (op_ == Token::ADD) {
     // Handle string addition here, because it is the only operation
     // that does not do a ToNumber conversion on the operands.
     GenerateStringAddCode(masm);
   }
 
   // Convert oddball arguments to numbers.
@@ skipping 3727 matching lines @@
   // Do a tail call to the rewritten stub.
   __ jmp(rdi);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64