[dart2wasm] Avoid using deep array copy in places where we only want to copy shallow

The `jsArrayFromDartList` method is a deep array copy: It will call out
to JS to allocate an array and initialize it by calling back to Dart for
each dart list element and `jsify()` each element (which may - if the
element is a list - call `jsArrayFromDartList` again).

For the use cases changed in this CL we know we have a `List<JSAny>` so
there's actually no reason to do this recursively, we only need to
allocate a JS array and fill in the elements from the dart list (without
any processing such as `jsify(0)`ing the elements).

We also add some fast cases to `List<JSAny?>.toJS` for
length=0/1/2/3

Change-Id: Idf82e104a743b883c8af0bd1b3b3234dff6e3d5b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/414780
Reviewed-by: Srujan Gaddam <[email protected]>
Commit-Queue: Martin Kustermann <[email protected]>

Author: mkustermann

sdk/lib/_internal/wasm/lib/js_array.dart

@@ -543,7 +543,7 @@ class JSArrayImpl<T extends JSAny?> implements List<T> {
         js.JS<WasmExternRef?>(
           '(a, t) => a.concat(t)',
           toExternRef,
-          other.toExternRef,
+          other.toJS.toExternRef,
         ),
       );
     } else {

sdk/lib/_internal/wasm/lib/js_helper.dart

@@ -83,11 +83,6 @@ extension StringToExternRef on String? {
           : jsStringFromDartString(this!).toExternRef;
 }
 
-extension ListOfObjectToExternRef on List<Object?>? {
-  WasmExternRef? get toExternRef =>
-      this == null ? WasmExternRef.nullRef : jsArrayFromDartList(this!);
-}
-
 extension JSValueToExternRef on JSValue? {
   WasmExternRef? get toExternRef => JSValue.unbox(this);
 }
@@ -533,7 +528,7 @@ ByteBuffer toDartByteBuffer(WasmExternRef? ref) =>
     toDartByteData(
       callConstructorVarArgsRaw(
         getConstructorString('DataView'),
-        [JSValue(ref)].toExternRef,
+        [JSValue(ref) as JSAny].toJS.toExternRef,
       ),
     ).buffer;
 
@@ -571,7 +566,48 @@ List<int> jsIntTypedArrayToDartIntTypedData(
 }
 
 JSArray<T> toJSArray<T extends JSAny?>(List<T> list) {
-  int length = list.length;
+  final length = list.length;
+
+  if (length <= 4) {
+    if (length == 0) {
+      return JSArray<T>.withLength(0);
+    }
+    final list0 = list[0].toExternRef;
+    if (length == 1) {
+      return JSValue(JS<WasmExternRef>("o => [o]", list0)) as JSArray<T>;
+    }
+    final list1 = list[1].toExternRef;
+    if (length == 2) {
+      return JSValue(JS<WasmExternRef>("(o0, o1) => [o0, o1]", list0, list1))
+          as JSArray<T>;
+    }
+    final list2 = list[2].toExternRef;
+    if (length == 3) {
+      return JSValue(
+            JS<WasmExternRef>(
+              "(o0, o1, o2) => [o0, o1, o2]",
+              list0,
+              list1,
+              list2,
+            ),
+          )
+          as JSArray<T>;
+    }
+    final list3 = list[3].toExternRef;
+    if (length == 4) {
+      return JSValue(
+            JS<WasmExternRef>(
+              "(o0, o1, o2, o3) => [o0, o1, o2, o3]",
+              list0,
+              list1,
+              list2,
+              list3,
+            ),
+          )
+          as JSArray<T>;
+    }
+  }
+
   JSArray<T> result = JSArray<T>.withLength(length);
   for (int i = 0; i < length; i++) {
     result[i] = list[i];

sdk/lib/_internal/wasm/lib/js_interop_unsafe_patch.dart

@@ -49,7 +49,7 @@ extension JSObjectUnsafeUtilExtension on JSObject {
         if (arg2 != null) arg2,
         if (arg3 != null) arg3,
         if (arg4 != null) arg4,
-      ].toExternRef,
+      ].toJS.toExternRef,
     ),
   );
 
@@ -59,7 +59,7 @@ extension JSObjectUnsafeUtilExtension on JSObject {
         callMethodVarArgsRaw(
           toExternRef,
           method.toExternRef,
-          (arguments ?? <JSAny?>[]).toExternRef,
+          (arguments ?? <JSAny?>[]).toJS.toExternRef,
         ),
       );
 
@@ -89,7 +89,7 @@ extension JSFunctionUnsafeUtilExtension on JSFunction {
         if (arg2 != null) arg2,
         if (arg3 != null) arg3,
         if (arg4 != null) arg4,
-      ].toExternRef,
+      ].toJS.toExternRef,
     ),
   );
 
@@ -98,7 +98,7 @@ extension JSFunctionUnsafeUtilExtension on JSFunction {
       _box<JSObject>(
         callConstructorVarArgsRaw(
           toExternRef,
-          (arguments ?? <JSAny?>[]).toExternRef,
+          (arguments ?? <JSAny?>[]).toJS.toExternRef,
         ),
       );
 }