dart2js cps: Global value numbering and loop-invariant code motion.

pkg/compiler/lib/src/cps_ir/share_final_fields.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_final_fields;
 
 import 'optimizers.dart';
 import 'cps_ir_nodes.dart';
 import 'loop_hierarchy.dart';
 import '../elements/elements.dart';
@@ skipping 104 matching lines @@
 
     if (primitive.objectIsNotNull) {
       // Determine how far the GetField can be lifted. The outermost loop that
       // contains the input binding should also contain the load.
       // Don't move above a refinement guard since that might be unsafe.
 
       // TODO(sra): We can move above a refinement guard provided the input is
       // still in scope and safe (non-null). We will have to replace
       // primitive.object with the most constrained refinement still in scope.
       Continuation referencedLoop =
-          lowestCommonAncestor(loopHeaderFor[refinedReceiver],
-                               currentLoopHeader);
+          loopHierarchy.lowestCommonAncestor(loopHeaderFor[refinedReceiver],
+                                             currentLoopHeader);
       if (referencedLoop != currentLoopHeader) {
         Continuation hoistTarget = getCurrentOuterLoop(scope: referencedLoop);
         LetCont loopBinding = hoistTarget.parent;
         node.remove();
         node.insertAbove(loopBinding);
         // Remove the hoisted operations from the environment after processing
         // the loop.
         loopHoistedGetters
             .putIfAbsent(hoistTarget, () => <GetField>[])
             .add(primitive);
@@ skipping 13 matching lines @@
     // TODO(24781): This query is incorrect for fields assigned only via
     //
     //     super.field = ...
     //
     // return backend.compiler.world.fieldNeverChanges(field);
 
     // Native fields are getters with side effects (e.g. layout).
     if (backend.isNative(field)) return false;
     return field.isFinal || field.isConst;
   }
-
-  /// Returns the the innermost loop that effectively encloses both
-  /// c1 and c2 (or `null` if there is no such loop).
-  Continuation lowestCommonAncestor(Continuation c1, Continuation c2) {
-    int d1 = getDepth(c1), d2 = getDepth(c2);
-    while (c1 != c2) {
-      if (d1 <= d2) {
-        c2 = loopHierarchy.getEnclosingLoop(c2);
-        d2 = getDepth(c2);
-      } else {
-        c1 = loopHierarchy.getEnclosingLoop(c1);
-        d1 = getDepth(c1);
-      }
-    }
-    return c1;
-  }
-
-  int getDepth(Continuation loop) {
-    if (loop == null) return -1;
-    return loopHierarchy.loopDepth[loop];
-  }
 }