Only emit typeguards if we think they are valuable.

lib/compiler/implementation/ssa/nodes.dart

Index: lib/compiler/implementation/ssa/nodes.dart
diff --git a/lib/compiler/implementation/ssa/nodes.dart b/lib/compiler/implementation/ssa/nodes.dart
index 795a2157aa1a57488bb51f6a124a09459822507d..42c4c7e4ac9d73d3132f3887e7127f372ec89c30 100644
--- a/lib/compiler/implementation/ssa/nodes.dart
+++ b/lib/compiler/implementation/ssa/nodes.dart
@@ -445,6 +445,11 @@ class HBasicBlock extends HInstructionList implements Hashable {
   bool isLoopHeader() => blockInformation is HLoopInformation;
   bool isLabeledBlock() => blockInformation is HLabeledBlockInformation;
 
+  HBasicBlock getEnclosingLoopHeader() {

[kasperl, 2012/04/20 12:07:31]

Maybe drop the 'get' prefix?

[floitsch, 2012/04/20 12:43:47]

How would you know it's not just a field (like parentLoopHeader) then? Or do you
want me to make it a getter?

[kasperl, 2012/04/20 12:52:14]

Like I know hashCode() isn't a field :-)

[floitsch, 2012/04/20 13:51:21]

I let Nicolas decide: now it's a getter :)

+    if (isLoopHeader()) return this;
+    return parentLoopHeader;
+  }
+
   bool hasGuards() => !guards.isEmpty();
 
   void open() {