1 /*
   2  * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package jdk.nashorn.internal.ir;
  27 
  28 import java.util.ArrayDeque;
  29 import java.util.ArrayList;
  30 import java.util.Deque;
  31 import java.util.List;
  32 import java.util.ListIterator;
  33 
  34 /**
  35  * This is a subclass of lexical context used for filling
  36  * blocks (and function nodes) with statements. When popping
  37  * a block from the lexical context, any statements that have
  38  * been generated in it are commited to the block. This saves
  39  * unnecessary object mutations and lexical context replacement
  40  */
  41 public class BlockLexicalContext extends LexicalContext {
  42     /** statement stack, each block on the lexical context maintains one of these, which is
  43      *  committed to the block on pop */
  44     private Deque<List<Statement>> sstack = new ArrayDeque<>();
  45 
  46     /** Last non debug statement emitted in this context */
  47     protected Statement lastStatement;
  48 
  49     @Override
  50     public <T extends LexicalContextNode> T push(final T node) {
  51         T pushed = super.push(node);
  52         if (node instanceof Block) {
  53             sstack.push(new ArrayList<Statement>());
  54         }
  55         return pushed;
  56     }
  57 
  58     /**
  59      * Get the statement list from the stack, possibly filtered
  60      * @return statement list
  61      */
  62     protected List<Statement> popStatements() {
  63         return sstack.pop();
  64     }
  65 
  66     @Override
  67     public <T extends LexicalContextNode> T pop(final T node) {
  68         T expected = node;
  69         if (node instanceof Block) {
  70             final List<Statement> newStatements = popStatements();
  71             expected = (T)((Block)node).setStatements(this, newStatements);
  72             if (!sstack.isEmpty()) {
  73                 lastStatement = lastStatement(sstack.peek());
  74             }
  75         }
  76         return super.pop(expected);
  77     }
  78 
  79     /**
  80      * Append a statement to the block being generated
  81      * @param statement statement to add
  82      */
  83     public void appendStatement(final Statement statement) {
  84         assert statement != null;
  85         sstack.peek().add(statement);
  86         lastStatement = statement;
  87     }
  88 
  89     /**
  90      * Prepend a statement to the block being generated
  91      * @param statement statement to prepend
  92      * @return the prepended statement
  93      */
  94     public Node prependStatement(final Statement statement) {
  95         assert statement != null;
  96         sstack.peek().add(0, statement);
  97         return statement;
  98     }
  99 
 100     /**
 101      * Get the last statement that was emitted into a block
 102      * @return the last statement emitted
 103      */
 104     public Statement getLastStatement() {
 105         return lastStatement;
 106     }
 107 
 108     private static Statement lastStatement(final List<Statement> statements) {
 109         for (final ListIterator<Statement> iter = statements.listIterator(statements.size()); iter.hasPrevious(); ) {
 110             final Statement node = iter.previous();
 111             return node;
 112         }
 113         return null;
 114     }
 115 }