Generate code for some switch statements.

dart/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.
 
 interface OptimizationPhase {
   String get name();
   void visitGraph(HGraph graph);
 }
 
 class SsaOptimizerTask extends CompilerTask {
@@ skipping 308 matching lines @@
     // phis that they might use.
     // NOTICE: Doesn't handle circular references, but we don't currently
     // create any.
     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)) {
+        if (!livePhis.contains(current) && current.usedBy.isEmpty()) {

[ahe, 2012/03/05 22:58:35]

Not sure about this.

[Lasse Reichstein Nielsen, 2012/03/06 08:57:14]

If it isn't empty, we will hit an assert in removePhi.
If that is actually happening for you, we should make the removal smarter.
If we don't have cycles, a simple recursive removal of the usedBy elements would
work, but if we do have cycles we need to break the cycle somehow (e.g.,
removing the phi from the inputs of its usedBy elements - we know that those
must be dead phis too).

[ahe, 2012/03/06 09:16:50]

I don't understand what you're talking about. I don't have good understanding of
this part of the compiler. I can add a TODO if you tell me exactly what to write
in it.

           block.removePhi(current);
         }
         current = next;
       }
     }
   }
 }
 
 class SsaRedundantPhiEliminator implements OptimizationPhase {
   final String name = "SsaRedundantPhiEliminator";
@@ skipping 296 matching lines @@
         }
       }
       if (!canBeMoved) continue;
 
       // This is safe because we are running after GVN.
       // TODO(ngeoffray): ensure GVN has been run.
       set_.add(current);
     }
   }
 }