Port StringPrototypeConcat to Torque

Bug: v8:8996
Change-Id: Icb454f8ff5f0964b019f360e71119158341307de
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1622743
Commit-Queue: Z Nguyen-Huu <duongn@microsoft.com>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Simon Zünd <szuend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61756}

src/builtins/builtins-definitions.h

@@ -940,8 +940,6 @@ namespace internal {
   CPP(StringFromCodePoint)                                                     \
   /* ES6 #sec-string.fromcharcode */                                           \
   TFJ(StringFromCharCode, SharedFunctionInfo::kDontAdaptArgumentsSentinel)     \
-  /* ES6 #sec-string.prototype.concat */                                       \
-  TFJ(StringPrototypeConcat, SharedFunctionInfo::kDontAdaptArgumentsSentinel)  \
   /* ES6 #sec-string.prototype.includes */                                     \
   TFJ(StringPrototypeIncludes,                                                 \
       SharedFunctionInfo::kDontAdaptArgumentsSentinel)                         \

src/builtins/builtins-string-gen.cc

@@ -686,33 +686,6 @@ TF_BUILTIN(StringFromCharCode, CodeStubAssembler) {
   }
 }
 
-// ES6 String.prototype.concat(...args)
-// ES6 #sec-string.prototype.concat
-TF_BUILTIN(StringPrototypeConcat, CodeStubAssembler) {
-  // TODO(ishell): use constants from Descriptor once the JSFunction linkage
-  // arguments are reordered.
-  CodeStubArguments arguments(
-      this,
-      ChangeInt32ToIntPtr(Parameter(Descriptor::kJSActualArgumentsCount)));
-  TNode<Object> receiver = arguments.GetReceiver();
-  TNode<Context> context = CAST(Parameter(Descriptor::kContext));
-
-  // Check that {receiver} is coercible to Object and convert it to a String.
-  receiver = ToThisString(context, receiver, "String.prototype.concat");
-
-  // Concatenate all the arguments passed to this builtin.
-  VARIABLE(var_result, MachineRepresentation::kTagged);
-  var_result.Bind(receiver);
-  arguments.ForEach(
-      CodeStubAssembler::VariableList({&var_result}, zone()),
-      [this, context, &var_result](Node* arg) {
-        arg = ToString_Inline(context, arg);
-        var_result.Bind(CallStub(CodeFactory::StringAdd(isolate()), context,
-                                 var_result.value(), arg));
-      });
-  arguments.PopAndReturn(var_result.value());
-}
-
 void StringBuiltinsAssembler::StringIndexOf(
     Node* const subject_string, Node* const search_string, Node* const position,
     const std::function<void(Node*)>& f_return) {

src/builtins/string.tq

@@ -117,4 +117,20 @@ namespace string {
       return Undefined;
     }
   }
+
+  // ES6 String.prototype.concat(...args)
+  // ES6 #sec-string.prototype.concat
+  transitioning javascript builtin StringPrototypeConcat(
+      implicit context: Context)(receiver: Object, ...arguments): Object {
+    // Check that {receiver} is coercible to Object and convert it to a String.
+    let string: String = ToThisString(receiver, 'String.prototype.concat');
+
+    // Concatenate all the arguments passed to this builtin.
+    const length: intptr = Convert<intptr>(arguments.length);
+    for (let i: intptr = 0; i < length; i++) {
+      const temp: String = ToString_Inline(context, arguments[i]);
+      string = string + temp;
+    }
+    return string;
+  }
 }