Pass ClosedWorld directly to codegen tasks

pkg/compiler/lib/src/js_backend/backend.dart

Index: pkg/compiler/lib/src/js_backend/backend.dart
diff --git a/pkg/compiler/lib/src/js_backend/backend.dart b/pkg/compiler/lib/src/js_backend/backend.dart
index 1410cb06e222bc7346b9fe12ca48a3e9ee72b26a..2c1278855b7d214383b3dcd8118976fcf24f60c8 100644
--- a/pkg/compiler/lib/src/js_backend/backend.dart
+++ b/pkg/compiler/lib/src/js_backend/backend.dart
@@ -45,6 +45,7 @@ import '../js_emitter/js_emitter.dart' show CodeEmitterTask;
 import '../library_loader.dart' show LibraryLoader, LoadedLibraries;
 import '../native/native.dart' as native;
 import '../ssa/ssa.dart' show SsaFunctionCompiler;
+import '../tracer.dart';
 import '../tree/tree.dart';
 import '../types/types.dart';
 import '../universe/call_structure.dart' show CallStructure;
@@ -88,7 +89,7 @@ const VERBOSE_OPTIMIZER_HINTS = false;
 
 abstract class FunctionCompiler {
   /// Generates JavaScript code for `work.element`.
-  jsAst.Fun compile(CodegenWorkItem work);
+  jsAst.Fun compile(CodegenWorkItem work, ClosedWorld closedWorld);
 
   Iterable get tasks;
 }
@@ -559,6 +560,8 @@ class JavaScriptBackend extends Backend {
 
   final JSFrontendAccess frontend;
 
+  Tracer tracer;
+
   JavaScriptBackend(Compiler compiler,
       {bool generateSourceMap: true,
       bool useStartupEmitter: false,
@@ -898,8 +901,7 @@ class JavaScriptBackend extends Backend {
     if (elements.isEmpty) return false;
     return elements.any((element) {
       return selector.applies(element) &&
-          (mask == null ||
-              mask.canHit(element, selector, compiler.closedWorld));
+          (mask == null || mask.canHit(element, selector, _closedWorld));
     });
   }
 
@@ -955,11 +957,10 @@ class JavaScriptBackend extends Backend {
   }
 
   Set<ClassElement> nativeSubclassesOfMixin(ClassElement mixin) {
-    ClosedWorld closedWorld = compiler.closedWorld;
-    Iterable<MixinApplicationElement> uses = closedWorld.mixinUsesOf(mixin);
+    Iterable<MixinApplicationElement> uses = _closedWorld.mixinUsesOf(mixin);
     Set<ClassElement> result = null;
     for (MixinApplicationElement use in uses) {
-      closedWorld.forEachStrictSubclassOf(use, (ClassElement subclass) {
+      _closedWorld.forEachStrictSubclassOf(use, (ClassElement subclass) {
         if (isNativeOrExtendsNative(subclass)) {
           if (result == null) result = new Set<ClassElement>();
           result.add(subclass);
@@ -1499,7 +1500,7 @@ class JavaScriptBackend extends Backend {
       }
     }
 
-    jsAst.Fun function = functionCompiler.compile(work);
+    jsAst.Fun function = functionCompiler.compile(work, _closedWorld);
     if (function.sourceInformation == null) {
       function = function.withSourceInformation(
           sourceInformationStrategy.buildSourceMappedMarker());
@@ -1752,7 +1753,7 @@ class JavaScriptBackend extends Backend {
     if (!type.isRaw) return false;
     ClassElement classElement = type.element;
     if (isInterceptorClass(classElement)) return false;
-    return compiler.closedWorld.hasOnlySubclasses(classElement);
+    return _closedWorld.hasOnlySubclasses(classElement);
   }
 
   WorldImpact registerUsedElement(Element element, {bool forResolution}) {
@@ -2362,9 +2363,24 @@ class JavaScriptBackend extends Backend {
     jsInteropAnalysis.onQueueClosed();
   }
 
+  // TODO(johnniwinther): Create a CodegenPhase object for the backend to hold
+  // data only available during code generation.
+  ClosedWorld _closedWorldCache;
+  ClosedWorld get _closedWorld {
+    assert(invariant(NO_LOCATION_SPANNABLE, _closedWorldCache != null,
+        message: "ClosedWorld has not be set yet."));
+    return _closedWorldCache;
+  }
+
+  void set _closedWorld(ClosedWorld value) {
+    _closedWorldCache = value;
+  }
+
   WorldImpact onCodegenStart(ClosedWorld closedWorld) {
-    _namer = determineNamer(closedWorld);
-    emitter.createEmitter(_namer, closedWorld);
+    _closedWorld = closedWorld;
+    _namer = determineNamer(_closedWorld);
+    tracer = new Tracer(_closedWorld, namer, compiler.outputProvider);
+    emitter.createEmitter(_namer, _closedWorld);
     lookupMapAnalysis.onCodegenStart();
     if (hasIsolateSupport) {
       return enableIsolateSupport(forResolution: false);
@@ -2372,6 +2388,11 @@ class JavaScriptBackend extends Backend {
     return const WorldImpact();
   }
 
+  void onCodegenEnd() {
+    sourceInformationStrategy.onComplete();
+    tracer.close();
+  }
+
   /// Process backend specific annotations.
   void processAnnotations(
       Element element, ClosedWorldRefiner closedWorldRefiner) {