[builtins] Refactor the StringConstructor builtin

This patch removes the StringConstructor_ConstructStub builtin,
merging its functionality into the refactored StringConstructor
TurboFan builtin.

This brings us closer to our goal of deprecating the `construct_stub`
field in `SharedFunctionInfo`.

Bug: v8:7503
Change-Id: Ie98520c652f49dda91eff2fc51263611f29e0ebe
Reviewed-on: https://chromium-review.googlesource.com/942882
Commit-Queue: Mathias Bynens <mathias@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51660}

src/bootstrapper.cc

@@ -1937,7 +1937,7 @@ void Genesis::InitializeGlobal(Handle<JSGlobalObject> global_object,
         isolate->initial_object_prototype(), Builtins::kStringConstructor);
     string_fun->shared()->set_builtin_function_id(kStringConstructor);
     string_fun->shared()->SetConstructStub(
-        *BUILTIN_CODE(isolate, StringConstructor_ConstructStub));
+        *BUILTIN_CODE(isolate, JSBuiltinsConstructStub));
     string_fun->shared()->DontAdaptArguments();
     string_fun->shared()->set_length(1);
     InstallWithIntrinsicDefaultProto(isolate, string_fun,

src/builtins/builtins-constructor-gen.cc

@@ -732,79 +732,62 @@ TF_BUILTIN(NumberConstructor_ConstructStub, ConstructorBuiltinsAssembler) {
   args.PopAndReturn(result);
 }
 
-Node* ConstructorBuiltinsAssembler::EmitConstructString(Node* argc,
-                                                        CodeStubArguments& args,
-                                                        Node* context,
-                                                        bool convert_symbol) {
-  VARIABLE(var_result, MachineRepresentation::kTagged);
-
-  Label return_empty_string(this), to_string(this),
-      check_symbol(this, Label::kDeferred), done(this);
-
-  GotoIf(IntPtrEqual(IntPtrConstant(0), argc), &return_empty_string);
-
-  Node* argument = args.AtIndex(0);
+// https://tc39.github.io/ecma262/#sec-string-constructor
+TF_BUILTIN(StringConstructor, ConstructorBuiltinsAssembler) {
+  Node* context = Parameter(BuiltinDescriptor::kContext);
+  Node* argc =
+      ChangeInt32ToIntPtr(Parameter(BuiltinDescriptor::kArgumentsCount));
+  CodeStubArguments args(this, argc);
 
-  GotoIf(TaggedIsSmi(argument), &to_string);
+  Node* new_target = Parameter(BuiltinDescriptor::kNewTarget);
+  Node* target = LoadFromFrame(StandardFrameConstants::kFunctionOffset,
+                               MachineType::TaggedPointer());
 
-  Node* instance_type = LoadInstanceType(argument);
+  // 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);
 
-  Label* non_string = convert_symbol ? &check_symbol : &to_string;
-  GotoIfNot(IsStringInstanceType(instance_type), non_string);
-  {
-    var_result.Bind(argument);
-    Goto(&done);
-  }
+  // 2. Else,
+  //    a. If NewTarget is undefined [...]
+  Node* value = args.AtIndex(0);
+  Label if_tostring(this, &var_s);
+  GotoIfNot(IsUndefined(new_target), &if_tostring);
 
-  if (convert_symbol) {
-    BIND(&check_symbol);
-    GotoIfNot(IsSymbolInstanceType(instance_type), &to_string);
+  // 2a. [...] and Type(value) is Symbol, return SymbolDescriptiveString(value).
+  GotoIf(TaggedIsSmi(value), &if_tostring);
+  GotoIfNot(IsSymbol(value), &if_tostring);
   {
-      var_result.Bind(
-          CallRuntime(Runtime::kSymbolDescriptiveString, context, argument));
-      Goto(&done);
-    }
+    Node* result =
+        CallRuntime(Runtime::kSymbolDescriptiveString, context, value);
+    args.PopAndReturn(result);
   }
 
-  BIND(&to_string);
+  // 2b. Let s be ? ToString(value).
+  BIND(&if_tostring);
   {
-    var_result.Bind(ToString(context, argument));
-    Goto(&done);
+    var_s.Bind(CallBuiltin(Builtins::kToString, context, value));
+    Goto(&if_sloaded);
   }
 
-  BIND(&return_empty_string);
+  // 3. If NewTarget is undefined, return s.
+  BIND(&if_sloaded);
   {
-    var_result.Bind(EmptyStringConstant());
-    Goto(&done);
-  }
-
-  BIND(&done);
-  return var_result.value();
-}
-
-TF_BUILTIN(StringConstructor, ConstructorBuiltinsAssembler) {
-  Node* context = Parameter(BuiltinDescriptor::kContext);
-  Node* argc =
-      ChangeInt32ToIntPtr(Parameter(BuiltinDescriptor::kArgumentsCount));
-  CodeStubArguments args(this, argc);
-
-  args.PopAndReturn(EmitConstructString(argc, args, context, true));
-}
-
-TF_BUILTIN(StringConstructor_ConstructStub, ConstructorBuiltinsAssembler) {
-  Node* target = LoadFromFrame(StandardFrameConstants::kFunctionOffset,
-                               MachineType::TaggedPointer());
-  Node* new_target = Parameter(BuiltinDescriptor::kNewTarget);
-  Node* context = Parameter(BuiltinDescriptor::kContext);
+    Node* s_value = var_s.value();
+    Label return_s(this), constructstring(this, Label::kDeferred);
+    Branch(IsUndefined(new_target), &return_s, &constructstring);
 
-  Node* argc =
-      ChangeInt32ToIntPtr(Parameter(BuiltinDescriptor::kArgumentsCount));
-  CodeStubArguments args(this, argc);
+    BIND(&return_s);
+    { args.PopAndReturn(s_value); }
 
-  Node* string = EmitConstructString(argc, args, context, false);
-  Node* result = EmitFastNewObject(context, target, new_target);
-  StoreObjectField(result, JSValue::kValueOffset, string);
+    BIND(&constructstring);
+    {
+      Node* result =
+          CallBuiltin(Builtins::kFastNewObject, context, target, new_target);
+      StoreObjectField(result, JSValue::kValueOffset, s_value);
       args.PopAndReturn(result);
+    }
+  }
 }
 
 }  // namespace internal

src/builtins/builtins-constructor-gen.h

@@ -36,9 +36,6 @@ class ConstructorBuiltinsAssembler : public CodeStubAssembler {
   Node* EmitFastNewObject(Node* context, Node* target, Node* new_target,
                           Label* call_runtime);
 
-  Node* EmitConstructString(Node* argc, CodeStubArguments& args, Node* context,
-                            bool convert_symbol);
-
  private:
   Node* NotHasBoilerplate(Node* literal_site);
   Node* LoadAllocationSiteBoilerplate(Node* allocation_site);

src/builtins/builtins-definitions.h

@@ -968,9 +968,9 @@ namespace internal {
   CPP(AtomicsWake)                                                             \
                                                                                \
   /* String */                                                                 \
+  /* ES #sec-string-constructor */                                             \
   TFJ(StringConstructor, SharedFunctionInfo::kDontAdaptArgumentsSentinel)      \
-  TFJ(StringConstructor_ConstructStub,                                         \
-      SharedFunctionInfo::kDontAdaptArgumentsSentinel)                         \
+  /* ES #sec-string.fromcodepoint */                                           \
   CPP(StringFromCodePoint)                                                     \
   /* ES6 #sec-string.fromcharcode */                                           \
   TFJ(StringFromCharCode, SharedFunctionInfo::kDontAdaptArgumentsSentinel)     \

src/builtins/builtins.cc

@@ -262,10 +262,9 @@ bool Builtins::IsLazy(int index) {
     case kInterpreterEnterBytecodeAdvance:
     case kInterpreterEnterBytecodeDispatch:
     case kInterpreterEntryTrampoline:
-    case kPromiseConstructorLazyDeoptContinuation:  // crbug/v8/6786.
+    case kPromiseConstructorLazyDeoptContinuation:  // https://crbug/v8/6786.
     case kProxyConstructor_ConstructStub:     // https://crbug.com/v8/6787.
     case kNumberConstructor_ConstructStub:    // https://crbug.com/v8/6787.
-    case kStringConstructor_ConstructStub:    // https://crbug.com/v8/6787.
     case kTypedArrayConstructor_ConstructStub:  // https://crbug.com/v8/6787.
     case kProxyConstructor:                   // https://crbug.com/v8/6787.
     case kRecordWrite:  // https://crbug.com/chromium/765301.