Add an optional parameter to the dominatedUsers function in case we want to analyze the whole block,

lib/compiler/implementation/ssa/optimize.dart

 // Copyright (c) 2012, 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 1112 matching lines @@
   final String name = "SsaTypeconversionInserter";
   final Compiler compiler;
 
   SsaTypeConversionInserter(this.compiler);
 
   void visitGraph(HGraph graph) {
     visitDominatorTree(graph);
   }
 
 
   // Update users of [input] that are dominated by [:dominator.first:]

[kasperl, 2012/08/20 11:37:22]

Update comment.

   // to use [newInput] instead.
   void changeUsesDominatedBy(HBasicBlock dominator,
                              HInstruction input,
                              HType convertedType) {
     HTypeConversion newInput;
-    Set<HInstruction> dominatedUsers = input.dominatedUsers(dominator.first);
+    Set<HInstruction> dominatedUsers = input.dominatedUsers(null, dominator);
     for (HInstruction user in dominatedUsers) {

[kasperl, 2012/08/20 11:37:22]

How about returning if dominatedUsers.isEmpty and then just creating newInput
right away (outside the loop)? Seems cleaner than checking if newInput is null
inside the loop.

       if (newInput === null) {
         newInput = new HTypeConversion(convertedType, input);
         dominator.addBefore(dominator.first, newInput);
       }
       user.changeUse(input, newInput);
     }
   }
 
   void visitIs(HIs instruction) {
     HInstruction input = instruction.expression;
@@ skipping 179 matching lines @@
       // this type for the field is still a strong signal
       // indicating the expected type of the field.
       types[field] = type;
     } else {
       // If there are no invoked setters we know the type of
       // this field for sure.
       field.guaranteedType = type;
     }
   }
 }