Support break and labeled statements.

frog/leg/ssa/optimize.dart

 // Copyright (c) 2011, 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.
 
 class SsaOptimizerTask extends CompilerTask {
   SsaOptimizerTask(Compiler compiler) : super(compiler);
   String get name() => 'SSA optimizer';
 
   void optimize(WorkItem work, HGraph graph) {
     measure(() {
@@ skipping 277 matching lines @@
       HPhi phi = worklist.removeLast();
       for (final input in phi.inputs) {
         if (input is HPhi && !livePhis.contains(input)) {
           worklist.add(input);
           livePhis.add(input);
         }
       }
     }
 
     // Remove phis that are not live.
-    for (final block in graph.blocks) {
+    // Traverse in reverse order to remove phis with no uses before the
+    // phis that they might use.
+    // TODO(lrn): Handle cyclic usages.
+    List<HBasicBlock> blocks = graph.blocks;
+    for (int i = blocks.length - 1; i >= 0; i--) {
+      HBasicBlock block = blocks[i];
       HPhi current = block.phis.first;
       HPhi next = null;
       while (current != null) {
         next = current.next;
-        if (!livePhis.contains(current)) block.removePhi(current);
+        if (!livePhis.contains(current)) {
+          current.block.removePhi(current);
+        }
         current = next;
       }
     }
   }
 }
 
 class SsaRedundantPhiEliminator {
   void visitGraph(HGraph graph) {
     final List<HPhi> worklist = <HPhi>[];
 
@@ skipping 289 matching lines @@
         }
       }
       if (!canBeMoved) continue;
 
       // This is safe because we are running after GVN.
       // TODO(ngeoffray): ensure GVN has been run.
       set_.add(current);
     }
   }
 }