tree-ir: Do not merge captured parameters with other variables.

pkg/compiler/lib/src/tree_ir/optimization/variable_merger.dart

 // Copyright (c) 2015, 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.
 
 library tree_ir.optimization.variable_merger;
 
 import 'optimization.dart' show Pass;
 import '../tree_ir_nodes.dart';
 import '../../elements/elements.dart' show Local, ParameterElement;
 
@@ skipping 403 matching lines @@
   List<Variable> variables = interference.keys.toList();
   variables.sort((x, y) => interference[y].length - interference[x].length);
 
   Map<String, List<Variable>> registers = <String, List<Variable>>{};
   Map<Variable, Variable> subst = <Variable, Variable>{};
 
   // Parameters are special in that they must have a ParameterElement and
   // cannot be merged with each other. Ensure that they are not substituted.
   // Other variables can still be substituted by a parameter.
   for (Variable parameter in parameters) {
+    if (parameter.isCaptured) continue;

[asgerf, 2015/04/15 10:43:39]

This is a bug that snuck in with the last change.

     subst[parameter] = parameter;
     registers[group(parameter)] = <Variable>[parameter];
   }
 
   for (Variable v1 in variables) {
     // Parameters have already been assigned a substitute; skip those.
     if (subst.containsKey(v1)) continue;
 
     List<Variable> register = registers[group(v1)];
 
@@ skipping 106 matching lines @@
     // VariableDeclaration is only used for captured variables, which are never
     // merged, so this is not strictly necessary. But it's nicer if this class
     // works for arbitrary substitution maps.
     node.variable = replaceWrite(node.variable);
     node.value = visitExpression(node.value);
     node.next = visitStatement(node.next);
     return node;
   }
 
 }