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

pkg/compiler/lib/src/cps_ir/loop_hierarchy.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.loop_hierarchy;
 
 import 'cps_ir_nodes.dart';
 
 /// Determines the effective nesting of loops.
 ///
@@ skipping 132 matching lines @@
     }
     target = _markInnerLoop(target, catchLoop);
     for (Continuation cont in callContinuations) {
       // Store the loop target on each call continuation in the basic block.
       // Because we walk over call continuations as part of the basic block
       // traversal, these do not get their loop target set otherwise.
       loopTarget[cont] = target;
     }
     return target;
   }
+
+  /// 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 = getEnclosingLoop(c2);
+        d2 = getDepth(c2);
+      } else {
+        c1 = getEnclosingLoop(c1);
+        d1 = getDepth(c1);
+      }
+    }
+    return c1;
+  }
+
+  /// Returns the lexical nesting depth of [loop].
+  int getDepth(Continuation loop) {
+    if (loop == null) return 0;
+    return loopDepth[loop];
+  }
 }