Port StringPrototypeSlice to Torque

Bug: v8:8996
Change-Id: I712f7eea934581f8d0889889a8737548ef8fa255
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1611752
Commit-Queue: Z Nguyen-Huu <duongn@microsoft.com>
Reviewed-by: Simon Zünd <szuend@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Peter Wong <peter.wm.wong@gmail.com>
Cr-Commit-Position: refs/heads/master@{#61558}

BUILD.gn

@@ -968,6 +968,7 @@ torque_files = [
   "src/builtins/string-html.tq",
   "src/builtins/string-iterator.tq",
   "src/builtins/string-repeat.tq",
+  "src/builtins/string-slice.tq",
   "src/builtins/string-startswith.tq",
   "src/builtins/string-substring.tq",
   "src/builtins/typed-array-createtypedarray.tq",
@@ -1025,6 +1026,7 @@ torque_namespaces = [
   "string-html",
   "string-iterator",
   "string-repeat",
+  "string-slice",
   "string-substring",
   "test",
   "typed-array",

src/builtins/builtins-definitions.h

@@ -973,8 +973,6 @@ namespace internal {
   TFJ(StringPrototypeReplace, 2, kReceiver, kSearch, kReplace)                 \
   /* ES6 #sec-string.prototype.search */                                       \
   TFJ(StringPrototypeSearch, 1, kReceiver, kRegexp)                            \
-  /* ES6 #sec-string.prototype.slice */                                        \
-  TFJ(StringPrototypeSlice, SharedFunctionInfo::kDontAdaptArgumentsSentinel)   \
   /* ES6 #sec-string.prototype.split */                                        \
   TFJ(StringPrototypeSplit, SharedFunctionInfo::kDontAdaptArgumentsSentinel)   \
   /* ES6 #sec-string.prototype.substr */                                       \

src/builtins/builtins-string-gen.cc

@@ -1593,57 +1593,6 @@ TF_BUILTIN(StringPrototypeSearch, StringMatchSearchAssembler) {
   Generate(kSearch, "String.prototype.search", receiver, maybe_regexp, context);
 }
 
-// ES6 section 21.1.3.18 String.prototype.slice ( start, end )
-TF_BUILTIN(StringPrototypeSlice, StringBuiltinsAssembler) {
-  Label out(this);
-  TVARIABLE(IntPtrT, var_start);
-  TVARIABLE(IntPtrT, var_end);
-
-  const int kStart = 0;
-  const int kEnd = 1;
-  Node* argc =
-      ChangeInt32ToIntPtr(Parameter(Descriptor::kJSActualArgumentsCount));
-  CodeStubArguments args(this, argc);
-  Node* const receiver = args.GetReceiver();
-  TNode<Object> start = args.GetOptionalArgumentValue(kStart);
-  TNode<Object> end = args.GetOptionalArgumentValue(kEnd);
-  TNode<Context> context = CAST(Parameter(Descriptor::kContext));
-
-  // 1. Let O be ? RequireObjectCoercible(this value).
-  RequireObjectCoercible(context, receiver, "String.prototype.slice");
-
-  // 2. Let S be ? ToString(O).
-  TNode<String> const subject_string =
-      CAST(CallBuiltin(Builtins::kToString, context, receiver));
-
-  // 3. Let len be the number of elements in S.
-  TNode<IntPtrT> const length = LoadStringLengthAsWord(subject_string);
-
-  // Convert {start} to a relative index.
-  var_start = ConvertToRelativeIndex(context, start, length);
-
-  // 5. If end is undefined, let intEnd be len;
-  var_end = length;
-  GotoIf(IsUndefined(end), &out);
-
-  // Convert {end} to a relative index.
-  var_end = ConvertToRelativeIndex(context, end, length);
-  Goto(&out);
-
-  Label return_emptystring(this);
-  BIND(&out);
-  {
-    GotoIf(IntPtrLessThanOrEqual(var_end.value(), var_start.value()),
-           &return_emptystring);
-    TNode<String> const result =
-        SubString(subject_string, var_start.value(), var_end.value());
-    args.PopAndReturn(result);
-  }
-
-  BIND(&return_emptystring);
-  args.PopAndReturn(EmptyStringConstant());
-}
-
 TNode<JSArray> StringBuiltinsAssembler::StringToArray(
     TNode<Context> context, TNode<String> subject_string,
     TNode<Smi> subject_length, TNode<Number> limit_number) {

src/builtins/string-slice.tq

@@ -0,0 +1,35 @@
+// Copyright 2019 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.
+
+namespace string_slice {
+
+  extern macro SubString(String, intptr, intptr): String;
+
+  // ES6 #sec-string.prototype.slice ( start, end )
+  // https://tc39.github.io/ecma262/#sec-string.prototype.slice
+  transitioning javascript builtin StringPrototypeSlice(
+      implicit context: Context)(receiver: Object, ...arguments): String {
+    // 1. Let O be ? RequireObjectCoercible(this value).
+    // 2. Let S be ? ToString(O).
+    const string: String = ToThisString(receiver, 'String.prototype.slice');
+
+    // 3. Let len be the number of elements in S.
+    const length: intptr = string.length_intptr;
+
+    // Convert {start} to a relative index.
+    const start: intptr = ConvertToRelativeIndex(arguments[0], length);
+
+    // 5. If end is undefined, let intEnd be len;
+    // else Convert {end} to a relative index.
+    const temp = arguments[1];
+    const end: intptr =
+        temp == Undefined ? length : ConvertToRelativeIndex(temp, length);
+
+    if (end <= start) {
+      return kEmptyString;
+    }
+
+    return SubString(string, start, end);
+  }
+}