Add support for profile-based startup optimizations.

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

Index: pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart
diff --git a/pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart b/pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart
index d27eca3e384c64cd6d65620cdfc3a70fcd3d2bf7..3d7920c736dc2bd66902dab1b2dbaadbd093f656 100644
--- a/pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart
+++ b/pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart
@@ -4,6 +4,9 @@
 
 library dart2js.js_emitter.program_builder;
 
+import 'dart:io';
+import 'dart:convert' show JSON;
+
 import '../../closure.dart' show ClosureTask, ClosureFieldElement;
 import '../../common.dart';
 import '../../common/names.dart' show Names, Selectors;
@@ -67,10 +70,14 @@ import '../js_emitter.dart'
 import '../model.dart';
 import '../sorter.dart';
 
+part 'allocated_classes_profile.dart';
 part 'collector.dart';
 part 'field_visitor.dart';
 part 'registry.dart';
 
+const allocatedClassesPath =
+    const String.fromEnvironment("dart2js.allocatedClasses");

[sra1, 2017/05/02 20:40:12]

Can you make this a command-line option?

[floitsch, 2017/05/06 19:25:43]

done.

+
 /// Builds a self-contained representation of the program that can then be
 /// emitted more easily by the individual emitters.
 class ProgramBuilder {
@@ -266,7 +273,8 @@ class ProgramBuilder {
         _buildTypeToInterceptorMap(), _task.metadataCollector, finalizers,
         needsNativeSupport: needsNativeSupport,
         outputContainsConstantList: collector.outputContainsConstantList,
-        hasIsolateSupport: _backendUsage.isIsolateInUse);
+        hasIsolateSupport: _backendUsage.isIsolateInUse,
+        hasSoftDeferredClasses: _notSoftDeferred != null);
   }
 
   void _markEagerClasses() {
@@ -584,6 +592,49 @@ class ProgramBuilder {
         library, uri, statics, classes, staticFieldsForReflection);
   }
 
+  Set<ClassElement> _notSoftDeferred;
+
+  bool _isSoftDeferred(ClassElement element) {
+    if (_notSoftDeferred == null &&
+        (allocatedClassesPath != null || allocatedClassesJson != null)) {

[sra1, 2017/05/02 20:40:13]

Does this execute once?
Perhaps make it more clear by putting some code in a helper init method.

[floitsch, 2017/05/06 19:25:43]

done.

+      var blackList = [
+        'dart:_interceptors',
+        'dart:html',
+        'dart:typed_data_implementation',
+        'dart:_native_typed_data'
+      ].toSet();
+      String data = allocatedClassesPath != null
+          ? new File(allocatedClassesPath).readAsStringSync()
+          : allocatedClassesJson;
+      Set<String> allocatedClassesKeys = JSON.decode(data).keys.toSet();
+      Set<ClassElement> allocatedClasses = new Set<ClassElement>();
+
+      void collect(ClassElement element) {
+        allocatedClasses.add(element);
+        if (element.isMixinApplication) {
+          collect(computeMixinClass(element));
+        }
+        if (element.superclass != null) {
+          collect(element.superclass);
+        }
+      }
+
+      collector.outputClassLists.forEach((_, List<ClassElement> elements) {
+        for (ClassElement element in elements) {
+          var key = "${element.library.canonicalUri}:${element.name}";
+          if (allocatedClassesKeys.contains(key) ||
+              _nativeData.isJsInteropClass(element) ||
+              blackList.contains(element.library.canonicalUri.toString())) {
+            collect(element);
+          }
+        }
+      });
+      _notSoftDeferred = allocatedClasses;
+    }
+    if (_notSoftDeferred == null) return false;
+    return !_notSoftDeferred.contains(element);
+  }
+
   Class _buildClass(ClassElement element) {
     bool onlyForRti = collector.classesOnlyNeededForRti.contains(element);
     bool hasRtiField = _rtiNeed.classNeedsRtiField(element);
@@ -752,7 +803,8 @@ class ProgramBuilder {
           hasRtiField: hasRtiField,
           onlyForRti: onlyForRti,
           isNative: _nativeData.isNativeClass(element),
-          isClosureBaseClass: isClosureBaseClass);
+          isClosureBaseClass: isClosureBaseClass,
+          isSoftDeferred: _isSoftDeferred(element));
     }
     _classes[element] = result;
     return result;