Optimize getField by caching a closure generated from eval.

runtime/lib/mirrors_impl.dart

Index: runtime/lib/mirrors_impl.dart
diff --git a/runtime/lib/mirrors_impl.dart b/runtime/lib/mirrors_impl.dart
index 310c9f7b48b997589ce658ab2ed42fdff2009365..baca1e56fe32d48e0624e3d8cab9b4ce98a15dda 100644
--- a/runtime/lib/mirrors_impl.dart
+++ b/runtime/lib/mirrors_impl.dart
@@ -332,6 +332,52 @@ class _LocalInstanceMirror extends _LocalObjectMirror
     return new _InvocationTrampoline(this, selector);
   }
 
+  // TODO(16539): Make these weak.

[kasperl, 2014/02/05 08:34:26]

I guess there's no need for complex weak handling here. You never hand out
references to these closures (you just call them) so you could just clear the
maps on GC.

[rmacnak, 2014/02/05 18:53:41]

Soft would do as well. Though I wonder if this would still be a net win if there
are high levels of allocation and getField...

+  static Map _getFieldClosures = new HashMap();
+  static Map _setFieldClosures = new HashMap();
+
+  InstanceMirror getField(Symbol memberName) {
+    var f = _getFieldClosures[_n(memberName)];
+    if (f == null) {

[kasperl, 2014/02/05 08:32:13]

Consider splitting this method in two so it becomes more realistic to inline the
outer without the inner.

  InstanceMirror getField(Symbol memberName) {
    var closure = _getFieldClosures[_n(memberName)];
    return (closure == null) 
        ? _getFieldSlow(memberName)
        : reflect(closure(_reflectee));
  }

+      var unwrapped = _n(memberName);

[kasperl, 2014/02/05 08:32:13]

Cache _n(memberName) in a local?

[kasperl, 2014/02/05 09:05:40]

I guess what I meant was: Use unwrapped consistently below.

+      var at_pos = unwrapped.indexOf('@');

[kasperl, 2014/02/05 08:32:13]

Follow Dart coding style: at_pos -> atPosition or atIndex.

+      if (at_pos == -1) {
+        // Public symbol.
+        f = _eval('(x) => x.$unwrapped', null);
+      } else {
+        // Private symbol.
+        var withoutKey = unwrapped.substring(0, at_pos);
+        var privateKey = unwrapped.substring(at_pos);
+        f = _eval('(x) => x.$withoutKey', privateKey);
+      }
+      _getFieldClosures[_n(memberName)] = f;
+    }
+    return reflect(f(_reflectee));
+  }
+
+  InstanceMirror setField(Symbol memberName, arg) {
+    var f = _setFieldClosures[_n(memberName)];

[kasperl, 2014/02/05 08:32:13]

Cache _n(memberName) in a local?

+    if (f == null) {
+      var unwrapped = _n(memberName);
+      var at_pos = unwrapped.indexOf('@');

[kasperl, 2014/02/05 08:32:13]

Follow Dart coding style: at_pos -> atPosition or atIndex.

+      if (at_pos == -1) {
+        // Public symbol.
+        f = _eval('(x, v) => x.$unwrapped = v', null);
+      } else {
+        // Private symbol.
+        var withoutKey = unwrapped.substring(0, at_pos);
+        var privateKey = unwrapped.substring(at_pos);
+        f = _eval('(x, v) => x.$withoutKey = v', privateKey);
+      }
+      _setFieldClosures[_n(memberName)] = f;
+    }
+    f(_reflectee, arg);
+    return reflect(arg);
+  }  
+
+  static _eval(expression, privateKey)
+      native "Mirrors_evalInLibraryWithPrivateKey";
+
   // Override to include the receiver in the arguments.
   InstanceMirror invoke(Symbol memberName,
                         List positionalArguments,