Bug 1770048: Improve self-hosted new_List (ESR) r=jandem,tcampbell, a=dsmith

Differential Revision: https://phabricator.services.mozilla.com/D146774

js/src/builtin/Array.cpp

@@ -4243,3 +4243,35 @@ JS_PUBLIC_API bool JS::SetArrayLength(JSContext* cx, Handle<JSObject*> obj,
 
   return SetLengthProperty(cx, obj, length);
 }
+
+bool js::intrinsic_newList(JSContext* cx, unsigned argc, js::Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  MOZ_ASSERT(args.length() == 0);
+
+  size_t length = 0;
+  gc::AllocKind allocKind = GuessArrayGCKind(length);
+  MOZ_ASSERT(CanChangeToBackgroundAllocKind(allocKind, &ArrayObject::class_));
+  allocKind = ForegroundToBackgroundAllocKind(allocKind);
+
+  /*
+   * Get a shape with zero fixed slots, regardless of the size class.
+   * See JSObject::createArray.
+   */
+  RootedShape shape(
+      cx, SharedShape::getInitialShape(cx, &ArrayObject::class_, cx->realm(),
+                                       TaggedProto(), gc::AllocKind::OBJECT0));
+  if (!shape) {
+    return false;
+  }
+
+  gc::InitialHeap heap = gc::InitialHeap::DefaultHeap;
+  AutoSetNewObjectMetadata metadata(cx);
+  RootedArrayObject list(cx, ArrayObject::createArray(cx, allocKind, heap,
+                                                      shape, length, metadata));
+  if (!list || !AddLengthProperty(cx, list)) {
+    return false;
+  }
+
+  args.rval().setObject(*list);
+  return true;
+}

js/src/builtin/Array.h

@@ -116,6 +116,8 @@ extern bool array_slice(JSContext* cx, unsigned argc, js::Value* vp);
 extern JSObject* ArraySliceDense(JSContext* cx, HandleObject obj, int32_t begin,
                                  int32_t end, HandleObject result);
 
+extern bool intrinsic_newList(JSContext* cx, unsigned argc, js::Value* vp);
+
 /*
  * Append the given (non-hole) value to the end of an array.  The array must be
  * a newborn array -- that is, one which has not been exposed to script for

js/src/builtin/Module.js

@@ -14,7 +14,7 @@ function CallModuleResolveHook(module, moduleRequest, expectedMinimumStatus)
 
 // https://tc39.es/ecma262/#sec-getexportednames
 // ES2020 15.2.1.17.2 GetExportedNames
-function ModuleGetExportedNames(exportStarSet = [])
+function ModuleGetExportedNames(exportStarSet = new_List())
 {
     if (!IsObject(this) || !IsModule(this)) {
         return callFunction(CallModuleMethodIfWrapped, this, exportStarSet,
@@ -26,13 +26,13 @@ function ModuleGetExportedNames(exportStarSet = [])
 
     // Step 4
     if (callFunction(ArrayIncludes, exportStarSet, module))
-        return [];
+        return new_List();
 
     // Step 5
     DefineDataProperty(exportStarSet, exportStarSet.length, module);
 
     // Step 6
-    let exportedNames = [];
+    let exportedNames = new_List();
     let namesCount = 0;
 
     // Step 7
@@ -99,7 +99,7 @@ function ModuleSetStatus(module, newStatus)
 //  - If the request is found to be ambiguous, the string `"ambiguous"` is
 //    returned.
 //
-function ModuleResolveExport(exportName, resolveSet = [])
+function ModuleResolveExport(exportName, resolveSet = new_List())
 {
     assert(typeof exportName === "string", "ModuleResolveExport");
 
@@ -206,7 +206,7 @@ function GetModuleNamespace(module)
     // Step 4
     if (typeof namespace === "undefined") {
         let exportedNames = callFunction(module.getExportedNames, module);
-        let unambiguousNames = [];
+        let unambiguousNames = new_List();
         for (let i = 0; i < exportedNames.length; i++) {
             let name = exportedNames[i];
             let resolution = callFunction(module.resolveExport, module, name);
@@ -312,7 +312,7 @@ function ModuleInstantiate()
     }
 
     // Step 3
-    let stack = [];
+    let stack = new_List();
 
     // Steps 4-5
     try {
@@ -606,7 +606,7 @@ function ModuleEvaluate()
     }
 
     // Step 4
-    let stack = [];
+    let stack = new_List();
 
     // Steps 5-6
     try {
@@ -769,7 +769,7 @@ function InnerModuleEvaluation(module, stack, index)
 }
 
 // https://tc39.es/proposal-top-level-await/#sec-gather-async-parent-completions
-function GatherAsyncParentCompletions(module, execList = []) {
+function GatherAsyncParentCompletions(module, execList = new_List()) {
   assert(module.status == MODULE_STATUS_EVALUATED, "bad status for async module");
 
   // Step 5.
@@ -809,4 +809,3 @@ function ExecuteAsyncModule(module) {
 
   ExecuteModule(module);
 }
-

js/src/builtin/RegExp.js

@@ -349,7 +349,7 @@ function RegExpReplaceSlowPath(rx, S, lengthS, replaceValue,
     }
 
     // Step 9.
-    var results = [];
+    var results = new_List();
     var nResults = 0;
 
     // Step 11.
@@ -456,7 +456,7 @@ function RegExpGetComplexReplacement(result, matched, S, position,
                                      functionalReplace, firstDollarIndex)
 {
     // Step 14.h.
-    var captures = [];
+    var captures = new_List();
     var capturesLength = 0;
 
     // Step 14.k.i (reordered).
@@ -546,7 +546,7 @@ function RegExpGetFunctionalReplacement(result, S, position, replaceValue) {
     }
 
     // Steps 14.g-i, 14.k.i-ii.
-    var captures = [];
+    var captures = new_List();
     for (var n = 0; n <= nCaptures; n++) {
         assert(typeof result[n] === "string" || result[n] === undefined,
                "RegExpMatcher returns only strings and undefined");

js/src/builtin/Utilities.js

@@ -27,16 +27,7 @@
 // code are installed via the std_functions JSFunctionSpec[] in
 // SelfHosting.cpp.
 
-/********** List / Record specification types **********/
-
-// A "List" is an internal type used in the ECMAScript spec to define a simple
-// ordered list of values. It is never exposed to user script, but we use a
-// simple Object (with null prototype) as a convenient implementation.
-//
-// NOTE: This does not track a `length` field.
-function new_List() {
-    return std_Object_create(null);
-}
+/********** Specification types **********/
 
 
 // A "Record" is an internal type used in the ECMAScript spec to define a struct

js/src/vm/SelfHosting.cpp

@@ -2386,7 +2386,7 @@ static const JSFunctionSpec intrinsic_functions[] = {
     JS_INLINABLE_FN("UnsafeSetReservedSlot", intrinsic_UnsafeSetReservedSlot, 3,
                     0, IntrinsicUnsafeSetReservedSlot),
 
-    // Intrinsics and standard functions used by Intl API implementation.
+// Intrinsics and standard functions used by Intl API implementation.
 #ifdef JS_HAS_INTL_API
     JS_FN("intl_BestAvailableLocale", intl_BestAvailableLocale, 3, 0),
     JS_FN("intl_CallCollatorMethodIfWrapped",
@@ -2476,6 +2476,7 @@ static const JSFunctionSpec intrinsic_functions[] = {
 #endif  // JS_HAS_INTL_API
 
     // Standard builtins used by self-hosting.
+    JS_FN("new_List", intrinsic_newList, 0, 0),
     JS_INLINABLE_FN("std_Array", array_construct, 1, 0, Array),
     JS_INLINABLE_FN("std_Array_pop", array_pop, 0, 0, ArrayPop),
     JS_INLINABLE_FN("std_Array_push", array_push, 1, 0, ArrayPush),