dart2js cps: Generate interceptors at use-site and share afterwards.

pkg/compiler/lib/src/cps_ir/share_interceptors.dart

+// Copyright (c) 2015, 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.
+
+library dart2js.cps_ir.share_interceptors;
+
+import 'cps_ir_nodes.dart';
+import 'optimizers.dart';
+
+/// Merges calls to `getInterceptor` when one call dominates the other.
+/// 
+/// Should run after [LoopInvariantCodeMotion] so interceptors lifted out from
+/// loops can be merged.
+class ShareInterceptors extends RecursiveVisitor implements Pass {
+  String get passName => 'Share interceptors';
+
+  final Map<Primitive, Interceptor> interceptorFor = 
+      <Primitive, Interceptor>{};
+
+  void rewrite(FunctionDefinition node) {
+    visit(node.body);
+  }
+
+  @override
+  Expression traverseLetPrim(LetPrim node) {
+    if (node.primitive is Interceptor) {
+      Interceptor interceptor = node.primitive;
+      Primitive input = interceptor.input.definition;
+      Interceptor existing = interceptorFor[input];
+      if (existing != null) {
+        existing.interceptedClasses.addAll(interceptor.interceptedClasses);
+        existing.substituteFor(interceptor);
+      } else {
+        interceptorFor[input] = interceptor;
+        pushAction(() {
+          interceptorFor.remove(input);
+        });
+      }
+    }
+    return node.body;
+  }
+}