dart2js cps: Hoist loop-invariant branches from loop entry.

pkg/compiler/lib/src/cps_ir/cps_fragment.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 cps_ir.cps_fragment;
 
 import 'cps_ir_nodes.dart';
 import '../constants/values.dart';
 import '../universe/selector.dart' show Selector;
 import '../types/types.dart' show TypeMask;
@@ skipping 171 matching lines @@
 
   /// Continue a loop started by [beginLoop].
   ///
   /// This closes the fragment; no more nodes may be inserted.
   void continueLoop(Continuation cont, [List<Primitive> updatedLoopVariables]) {
     put(new InvokeContinuation(cont, updatedLoopVariables, isRecursive: true));
   }
 
   /// Branch on [condition].
   ///
+  /// Returns a new fragment for the 'then' branch, or the 'else' branch
+  /// if [negate] is true.
+  ///
+  /// The other branch becomes the new hole.
+  CpsFragment branch(Primitive condition,
+                     {bool negate: false,
+                      bool strict: false}) {
+    Continuation trueCont = new Continuation(<Parameter>[]);
+    Continuation falseCont = new Continuation(<Parameter>[]);
+    put(new LetCont.two(trueCont, falseCont,
+            new Branch(condition, trueCont, falseCont, strict: strict)));
+    if (negate) {
+      context = trueCont;
+      return new CpsFragment(sourceInformation, falseCont);
+    } else {
+      context = falseCont;
+      return new CpsFragment(sourceInformation, trueCont);
+    }
+  }
+
+  /// Branch on [condition].
+  ///
   /// Returns a new fragment for the 'then' branch.
   ///
   /// The 'else' branch becomes the new hole.
-  CpsFragment ifTruthy(Primitive condition) {
-    Continuation trueCont = new Continuation(<Parameter>[]);
-    Continuation falseCont = new Continuation(<Parameter>[]);
-    put(new LetCont.two(trueCont, falseCont,
-            new Branch.loose(condition, trueCont, falseCont)));
-    context = falseCont;
-    return new CpsFragment(sourceInformation, trueCont);
-  }
+  CpsFragment ifTruthy(Primitive condition) => branch(condition);
 
   /// Branch on [condition].
   ///
   /// Returns a new fragment for the 'else' branch.
   ///
   /// The 'then' branch becomes the new hole.
-  CpsFragment ifFalsy(Primitive condition) {
-    Continuation trueCont = new Continuation(<Parameter>[]);
-    Continuation falseCont = new Continuation(<Parameter>[]);
-    put(new LetCont.two(trueCont, falseCont,
-            new Branch.loose(condition, trueCont, falseCont)));
-    context = trueCont;
-    return new CpsFragment(sourceInformation, falseCont);
-  }
+  CpsFragment ifFalsy(Primitive condition) => branch(condition, negate: true);
 
   /// Create a new empty continuation and bind it here.
   ///
   /// Convenient for making a join point where multiple branches
   /// meet later.
   ///
   /// The LetCont body becomes the new hole.
   ///
   /// Example use:
   ///
@@ skipping 130 matching lines @@
   while (prim.firstRef != null) {
     Refinement refine = prim.firstRef.parent;
     destroyRefinementsOfDeadPrimitive(refine);
     LetPrim letPrim = refine.parent;
     InteriorNode parent = letPrim.parent;
     parent.body = letPrim.body;
     letPrim.body.parent = parent;
     prim.firstRef.unlink();
   }
 }