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 @@
     while (!worklist.isEmpty()) {
       HPhi phi = worklist.removeLast();
       for (final input in phi.inputs) {
         if (input is HPhi && !livePhis.contains(input)) {
           worklist.add(input);
           livePhis.add(input);
         }
       }
     }
 
+    recursiveRemove(HPhi phi) {
+      while (!phi.usedBy.isEmpty()) {
+        recursiveRemove(phi.usedBy[0]);

[floitsch, 2012/02/20 19:01:54]

are you sure this can't yield an infinite loop?

[Lasse Reichstein Nielsen, 2012/02/21 13:53:56]

Not absolutely. I guess we could have recursive dependencies between phis in a
loop. I'll have to check.
Alternatively, I can just remove this phi as an input of the ones that uses it,
before removing itself (removePhi doesn't work if the phi has uses, and if we
can have cycles, we would need to break it somehow, so might as well do it
here).

+      }
+      phi.block.removePhi(phi);
+    }
+
     // Remove phis that are not live.
     for (final block in graph.blocks) {
       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)) {
+          // Remove any (dead phi) uses of current before removing current.
+          recursiveRemove(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);
     }
   }
 }