[turbofan] Use StringAddStub if either input to JSAdd is a string.

src/compiler/js-typed-lowering.cc

 // Copyright 2014 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/code-factory.h"
 #include "src/compilation-dependencies.h"
 #include "src/compiler/access-builder.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/js-typed-lowering.h"
 #include "src/compiler/linkage.h"
@@ skipping 353 matching lines @@
   if (r.BothInputsAre(Type::Number())) {
     // JSAdd(x:number, y:number) => NumberAdd(x, y)
     return r.ChangeToPureOperator(simplified()->NumberAdd(), Type::Number());
   }
   if (r.NeitherInputCanBe(Type::StringOrReceiver())) {
     // JSAdd(x:-string, y:-string) => NumberAdd(ToNumber(x), ToNumber(y))
     Node* frame_state = NodeProperties::GetFrameStateInput(node, 1);
     r.ConvertInputsToNumber(frame_state);
     return r.ChangeToPureOperator(simplified()->NumberAdd(), Type::Number());
   }
-  if (r.BothInputsAre(Type::String())) {
-    // JSAdd(x:string, y:string) => CallStub[StringAdd](x, y)
+  if (r.OneInputIs(Type::String())) {
+    StringAddFlags flags = STRING_ADD_CHECK_NONE;
+    if (!r.LeftInputIs(Type::String())) {
+      flags = STRING_ADD_CONVERT_LEFT;
+    } else if (!r.RightInputIs(Type::String())) {
+      flags = STRING_ADD_CONVERT_RIGHT;
+    }
+    // JSAdd(x:string, y) => CallStub[StringAdd](x, y)
+    // JSAdd(x, y:string) => CallStub[StringAdd](x, y)
     Callable const callable =
-        CodeFactory::StringAdd(isolate(), STRING_ADD_CHECK_NONE, NOT_TENURED);
+        CodeFactory::StringAdd(isolate(), flags, NOT_TENURED);
     CallDescriptor const* const desc = Linkage::GetStubCallDescriptor(
         isolate(), graph()->zone(), callable.descriptor(), 0,
         CallDescriptor::kNeedsFrameState, node->op()->properties());
     DCHECK_EQ(2, OperatorProperties::GetFrameStateInputCount(node->op()));
     node->RemoveInput(NodeProperties::FirstFrameStateIndex(node) + 1);
     node->InsertInput(graph()->zone(), 0,
                       jsgraph()->HeapConstant(callable.code()));
     NodeProperties::ChangeOp(node, common()->Call(desc));
     return Changed(node);
   }
@@ skipping 1419 matching lines @@
 }
 
 
 CompilationDependencies* JSTypedLowering::dependencies() const {
   return dependencies_;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8