[builtins] Port the String constructor to Torque

Bug: v8:8996
Change-Id: Ie21bf5b695370a89a2f1023cc14db8b7ff1a141e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1744641
Commit-Queue: Z Nguyen-Huu <duongn@microsoft.com>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63170}

src/builtins/builtins-constructor-gen.cc

@@ -739,66 +739,5 @@ TF_BUILTIN(GenericLazyDeoptContinuation, ConstructorBuiltinsAssembler) {
   Return(result);
 }
 
-// https://tc39.github.io/ecma262/#sec-string-constructor
-TF_BUILTIN(StringConstructor, ConstructorBuiltinsAssembler) {
-  Node* context = Parameter(Descriptor::kContext);
-  Node* argc =
-      ChangeInt32ToIntPtr(Parameter(Descriptor::kJSActualArgumentsCount));
-  CodeStubArguments args(this, argc);
-
-  TNode<Object> new_target = CAST(Parameter(Descriptor::kJSNewTarget));
-
-  // 1. If no arguments were passed to this function invocation, let s be "".
-  VARIABLE(var_s, MachineRepresentation::kTagged, EmptyStringConstant());
-  Label if_sloaded(this, &var_s);
-  GotoIf(WordEqual(argc, IntPtrConstant(0)), &if_sloaded);
-
-  // 2. Else,
-  //    a. If NewTarget is undefined [...]
-  Node* value = args.AtIndex(0);
-  Label if_tostring(this, &var_s);
-  GotoIfNot(IsUndefined(new_target), &if_tostring);
-
-  // 2a. [...] and Type(value) is Symbol, return SymbolDescriptiveString(value).
-  GotoIf(TaggedIsSmi(value), &if_tostring);
-  GotoIfNot(IsSymbol(value), &if_tostring);
-  {
-    Node* result =
-        CallRuntime(Runtime::kSymbolDescriptiveString, context, value);
-    args.PopAndReturn(result);
-  }
-
-  // 2b. Let s be ? ToString(value).
-  BIND(&if_tostring);
-  {
-    var_s.Bind(CallBuiltin(Builtins::kToString, context, value));
-    Goto(&if_sloaded);
-  }
-
-  // 3. If NewTarget is undefined, return s.
-  BIND(&if_sloaded);
-  {
-    Node* s_value = var_s.value();
-    Label return_s(this), constructstring(this, Label::kDeferred);
-    Branch(IsUndefined(new_target), &return_s, &constructstring);
-
-    BIND(&return_s);
-    { args.PopAndReturn(s_value); }
-
-    BIND(&constructstring);
-    {
-      // We are not using Parameter(Descriptor::kJSTarget) and loading the value
-      // from the current frame here in order to reduce register pressure on the
-      // fast path.
-      TNode<JSFunction> target = LoadTargetFromFrame();
-
-      Node* result =
-          CallBuiltin(Builtins::kFastNewObject, context, target, new_target);
-      StoreObjectField(result, JSPrimitiveWrapper::kValueOffset, s_value);
-      args.PopAndReturn(result);
-    }
-  }
-}
-
 }  // namespace internal
 }  // namespace v8

src/builtins/builtins-definitions.h

@@ -924,8 +924,6 @@ namespace internal {
   CPP(AtomicsWake)                                                             \
                                                                                \
   /* String */                                                                 \
-  /* ES #sec-string-constructor */                                             \
-  TFJ(StringConstructor, SharedFunctionInfo::kDontAdaptArgumentsSentinel)      \
   /* ES #sec-string.fromcodepoint */                                           \
   CPP(StringFromCodePoint)                                                     \
   /* ES6 #sec-string.fromcharcode */                                           \

src/builtins/string.tq

@@ -137,4 +137,46 @@ namespace string {
     }
     return string;
   }
+
+  extern transitioning runtime
+  SymbolDescriptiveString(implicit context: Context)(Object): Object;
+
+  // ES #sec-string-constructor
+  // https://tc39.github.io/ecma262/#sec-string-constructor
+  transitioning javascript builtin StringConstructor(
+      js-implicit context: Context, receiver: Object, newTarget: Object,
+      target: JSFunction)(...arguments): Object {
+    const length: intptr = Convert<intptr>(arguments.length);
+    let s: String;
+    // 1. If no arguments were passed to this function invocation, let s be "".
+    if (length == 0) {
+      s = EmptyStringConstant();
+    } else {
+      // 2. Else,
+      // 2. a. If NewTarget is undefined and Type(value) is Symbol, return
+      // SymbolDescriptiveString(value).
+      if (newTarget == Undefined) {
+        typeswitch (arguments[0]) {
+          case (value: Symbol): {
+            return SymbolDescriptiveString(value);
+          }
+          case (Object): {
+          }
+        }
+      }
+      // 2. b. Let s be ? ToString(value).
+      s = ToString_Inline(context, arguments[0]);
+    }
+    // 3. If NewTarget is undefined, return s.
+    if (newTarget == Undefined) {
+      return s;
+    }
+    // 4. Return ! StringCreate(s, ? GetPrototypeFromConstructor(NewTarget,
+    // "%String.prototype%")).
+    const map = GetDerivedMap(target, UnsafeCast<JSReceiver>(newTarget));
+    const obj =
+        UnsafeCast<JSPrimitiveWrapper>(AllocateFastOrSlowJSObjectFromMap(map));
+    obj.value = s;
+    return obj;
+  }
 }