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 664 matching lines @@
     node.block.addBefore(node, length);
 
     HBoundsCheck check = new HBoundsCheck(index, length);
     node.block.addBefore(node, check);
     return check;
   }
 
   HIntegerCheck insertIntegerCheck(HInstruction node, HInstruction value) {
     HIntegerCheck check = new HIntegerCheck(value);
     node.block.addBefore(node, check);
-    Set<HInstruction> dominatedUsers = value.dominatedUsers(check);
+    Set<HInstruction> dominatedUsers = value.dominatedUsers(node);
     for (HInstruction user in dominatedUsers) {
       user.changeUse(value, check);
     }
     return check;
   }
 
   void visitIndex(HIndex node) {
     if (!node.receiver.isIndexablePrimitive(types)) return;
     HInstruction index = node.index;
     if (index is HBoundsCheck) return;
@@ skipping 432 matching lines @@
   void visitGraph(HGraph graph) {
     visitDominatorTree(graph);
   }
 
 
   // Update users of [input] that are dominated by [:dominator.first:]
   // to use [newInput] instead.
   void changeUsesDominatedBy(HBasicBlock dominator,
                              HInstruction input,
                              HType convertedType) {
-    HTypeConversion newInput;
     Set<HInstruction> dominatedUsers = input.dominatedUsers(dominator.first);
-    for (HInstruction user in dominatedUsers) {
-      if (newInput === null) {
-        newInput = new HTypeConversion(convertedType, input);
-        dominator.addBefore(dominator.first, newInput);
-      }
+    if (dominatedUsers.isEmpty()) return;
+
+    HTypeConversion newInput = new HTypeConversion(convertedType, input);
+    dominator.addBefore(dominator.first, newInput);
+    dominatedUsers.forEach((HInstruction user) {
       user.changeUse(input, newInput);
-    }
+    });
   }
 
   void visitIs(HIs instruction) {
     HInstruction input = instruction.expression;
     HType convertedType =
         new HType.fromBoundedType(instruction.typeExpression, compiler);
 
     List<HInstruction> ifUsers = <HInstruction>[];
     List<HInstruction> notIfUsers = <HInstruction>[];
 
@@ skipping 173 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;
     }
   }
 }