[dart2wasm] Use the same Dart object when to{Upper,Lower}Case returns…

… the argument This fixes `identical` checks when the input doesn't need case mapping. This change was originally made in [1], but I'm trying to split it into smaller CLs as it currently has a lot of conflicts with the main branch. [1]: https://dart-review.googlesource.com/c/sdk/+/316628 Change-Id: I88da52a3a73c9d587acefe2b14fd39edaf01c966 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/332200 Reviewed-by: Aske Simon Christensen <[email protected]> Commit-Queue: Ömer Ağacan <[email protected]>
nguyencse · Nov 2, 2023 · d0a2656 · d0a2656
1 parent 12c4e22
commit d0a2656
Showing 1 changed file with 13 additions and 4 deletions.
diff --git a/sdk/lib/_internal/wasm/lib/js_string.dart b/sdk/lib/_internal/wasm/lib/js_string.dart
@@ -319,14 +319,20 @@ final class JSStringImpl implements String {
 
   @override
   String toLowerCase() {
-    return JSStringImpl(
-        js.JS<WasmExternRef?>('s => s.toLowerCase()', toExternRef));
+    final thisRef = toExternRef;
+    final lowerCaseRef = js.JS<WasmExternRef?>('s => s.toLowerCase()', thisRef);
+    return _jsIdentical(thisRef, lowerCaseRef)
+        ? this
+        : JSStringImpl(lowerCaseRef);
   }
 
   @override
   String toUpperCase() {
-    return JSStringImpl(
-        js.JS<WasmExternRef?>('s => s.toUpperCase()', toExternRef));
+    final thisRef = toExternRef;
+    final upperCaseRef = js.JS<WasmExternRef?>('s => s.toUpperCase()', thisRef);
+    return _jsIdentical(thisRef, upperCaseRef)
+        ? this
+        : JSStringImpl(upperCaseRef);
   }
 
   // Characters with Whitespace property (Unicode 6.3).
@@ -679,3 +685,6 @@ JSStringImpl _jsStringToJSStringImpl(WasmExternRef? string) =>
 @pragma("wasm:export", "\$jsStringFromJSStringImpl")
 WasmExternRef? _jsStringFromJSStringImpl(JSStringImpl string) =>
     string.toExternRef;
+
+bool _jsIdentical(WasmExternRef? ref1, WasmExternRef? ref2) =>
+    js.JS<bool>('Object.is', ref1, ref2);