dart2js cps: Clean up and avoid processing unreachable code.

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';
 
 /// Merges variables based on liveness and source variable information.
 ///
 /// This phase cleans up artifacts introduced by the translation through CPS,
 /// where each source variable is translated into several copies. The copies
 /// are merged again when they are not live simultaneously.
 class VariableMerger extends RecursiveVisitor implements Pass {
   String get passName => 'Variable merger';
 
   void rewrite(FunctionDefinition node) {
     rewriteFunction(node);
     visitStatement(node.body);
   }
 
-  @override
-  void visitInnerFunction(FunctionDefinition node) {
-    rewriteFunction(node);
-  }
-
   /// Rewrites the given function.
   /// This is called for the outermost function and inner functions.
   void rewriteFunction(FunctionDefinition node) {
     BlockGraphBuilder builder = new BlockGraphBuilder();
     builder.build(node);
     _computeLiveness(builder.blocks);
     Map<Variable, Variable> subst =
         _computeRegisterAllocation(builder.blocks, node.parameters);
     new SubstituteVariables(subst).apply(node);
   }
@@ skipping 67 matching lines @@
   /// Such variables cannot be merged with any other variables, so we exclude
   /// them from the control-flow graph entirely.
   Set<Variable> _ignoredVariables = new Set<Variable>();
 
   void build(FunctionDefinition node) {
     _currentBlock = newBlock();
     node.parameters.forEach(write);
     visitStatement(node.body);
   }
 
-  @override
-  void visitInnerFunction(FunctionDefinition node) {
-    // Do nothing. Inner functions are traversed in VariableMerger.
-  }
-
   /// Creates a new block with the current exception handler or [catchBlock]
   /// if provided.
   Block newBlock({Block catchBlock}) {
     if (catchBlock == null && _currentBlock != null) {
       catchBlock = _currentBlock.catchBlock;
     }
     Block block = new Block(catchBlock);
     blocks.add(block);
     return block;
   }
@@ skipping 369 matching lines @@
     return w;
   }
 
   void apply(FunctionDefinition node) {
     for (int i = 0; i < node.parameters.length; ++i) {
       node.parameters[i] = replaceWrite(node.parameters[i]);
     }
     node.body = visitStatement(node.body);
   }
 
-  @override
-  void visitInnerFunction(FunctionDefinition node) {
-    // Do nothing. Inner functions are traversed in VariableMerger.
-  }
-
   Expression visitVariableUse(VariableUse node) {
     node.variable = replaceRead(node.variable);
     return node;
   }
 
   Expression visitAssign(Assign node) {
     node.variable = replaceWrite(node.variable);
     node.value = visitExpression(node.value);
 
     // Remove assignments of form "x := x"
@@ skipping 12 matching lines @@
     node.expression = visitExpression(node.expression);
     node.next = visitStatement(node.next);
     if (node.expression is VariableUse) {
       VariableUse use = node.expression;
       --use.variable.readCount;
       return node.next;
     }
     return node;
   }
 }