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)
+            // TODO(ahe): Not sure the following is correct.

[ngeoffray, 2012/03/06 11:49:48]

Why did you need to add this? Was it on one test case or all?

[ahe, 2012/03/06 12:24:35]

Just one test case, I think.

[ngeoffray, 2012/03/06 12:32:55]

Worth fixing? I'd rather keep the bug and try to fix it the right way.

[ahe, 2012/03/06 13:10:51]

I wanted to get rid of the assertion error. This is one of the problematic
assertions I ranted about a few days ago. However, I could not figure out how to
turn it into an internal error.

I think a compiler crash is extremely bad, and I will do whatever it takes to
get rid of them.

As far as I understand, this change is semantically correct, but may generate
suboptimal code.

[ngeoffray, 2012/03/07 08:55:31]

But you're fixing a symptom, not the bug. I think we both agree that we
definitely prefer *failing* (not crashing) tests compared to adding symptom
fixes. To avoid the crash, why don't you do:

if (!current.usedBy.isEmpty()) compiler.internalError("blah", instruction: phi);

If this does not work, you could also file a bug and reference it here.

+            && current.usedBy.isEmpty()) {
           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);
     }
   }
 }