dart2js: Register constants in the model builder.

pkg/compiler/lib/src/js_emitter/registry.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart2js.js_emitter.program_builder;
 
 /// A Fragment maps [LibraryElement]s to their [Element]s.
 ///
 /// Fundamentally, this class nicely encapsulates a
 /// `Map<LibraryElement, List<Element>>`.
@@ skipping 36 matching lines @@
 /// This class assigns each registered element to its [Fragment] (which are in
 /// bijection with [OutputUnit]s).
 ///
 /// Registered holders are assigned a name.
 class Registry {
   final Compiler _compiler;
   final Map<String, Holder> _holdersMap = <String, Holder>{};
   final Map<OutputUnit, Fragment> _deferredFragmentsMap =
       <OutputUnit, Fragment>{};
 
+  /// Cache for the last seen output unit.
+  OutputUnit _lastOutputUnit;
+  Fragment _lastFragment;
+
   DeferredLoadTask get _deferredLoadTask => _compiler.deferredLoadTask;
   Iterable<Holder> get holders => _holdersMap.values;
   Iterable<Fragment> get deferredFragments => _deferredFragmentsMap.values;
   // Add one for the main fragment.
   int get fragmentCount => _deferredFragmentsMap.length + 1;
 
   Fragment mainFragment;
 
   Registry(this._compiler);
 
   bool get _isProgramSplit => _deferredLoadTask.isProgramSplit;
   OutputUnit get _mainOutputUnit => _deferredLoadTask.mainOutputUnit;
 
   Fragment _mapUnitToFragment(OutputUnit targetUnit) {
+    if (targetUnit == _lastOutputUnit) return _lastFragment;
+
     if (mainFragment == null) {
       mainFragment = new Fragment.main(_deferredLoadTask.mainOutputUnit);
     }
-    if (!_isProgramSplit) {
-      assert(targetUnit == _deferredLoadTask.mainOutputUnit);
-      return mainFragment;
+
+    Fragment result;
+    if (targetUnit == _mainOutputUnit) {
+      result = mainFragment;
+    } else {
+      String name = targetUnit.name;
+      result = _deferredFragmentsMap.putIfAbsent(
+          targetUnit, () => new Fragment.deferred(targetUnit, name));
     }
-    if (targetUnit == _mainOutputUnit) return mainFragment;
-    String name = targetUnit.name;
-    return _deferredFragmentsMap.putIfAbsent(
-        targetUnit, () => new Fragment.deferred(targetUnit, name));
+    _lastOutputUnit = targetUnit;
+    _lastFragment = result;
+    return result;
   }
 
   /// Adds all elements to their respective libraries in the correct fragment.
   void registerElements(OutputUnit outputUnit, List<Element> elements) {
     Fragment targetFragment = _mapUnitToFragment(outputUnit);
     for (Element element in Elements.sortedByPosition(elements)) {
       targetFragment.add(element.library, element);
     }
   }
 
+  void registerConstant(OutputUnit outputUnit, ConstantValue constantValue) {
+    // We just need to make sure that the target fragment is registered.
+    // Otherwise a fragment that contains only constants is not built.
+    _mapUnitToFragment(outputUnit);
+  }
+
   Holder registerHolder(String name) {
     return _holdersMap.putIfAbsent(
         name,
         () => new Holder(name, _holdersMap.length));
   }
 }