/*
* xtc - The eXTensible Compiler
* Copyright (C) 2004-2007 Robert Grimm
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* version 2 as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
* USA.
*/
package xtc.parser;
import java.util.Iterator;
import xtc.Constants;
import xtc.util.Runtime;
/**
* Visitor to eliminate dead productions. This visitor eliminates
* productions that are not reachable from top-level productions. It
* may perform faster if the grammar has previously been annotated
* with its real root.
*
* @see RootFinder
*
* @author Robert Grimm
* @version $Revision: 1.39 $
*/
public class DeadProductionEliminator extends GrammarVisitor {
/**
* Create a new dead production eliminator.
*
* @param runtime The runtime.
* @param analyzer The analyzer utility.
*/
public DeadProductionEliminator(Runtime runtime, Analyzer analyzer) {
super(runtime, analyzer);
}
/** Visit the specified grammar. */
public Object visit(Module m) {
// Initialize the per-grammar state.
analyzer.register(this);
analyzer.init(m);
// Mark all productions reachable from the top-level nonterminals.
if (m.hasProperty(Properties.ROOT)) {
dispatch((NonTerminal)m.getProperty(Properties.ROOT));
} else {
for (Production p : m.productions) {
if (p.hasAttribute(Constants.ATT_PUBLIC)) {
dispatch(p.name);
}
}
}
// Remove all productions that have not been marked.
for(Iterator<Production> iter = m.productions.iterator(); iter.hasNext();) {
Production p = iter.next();
if (! analyzer.isMarked(p.qName)) {
if (runtime.test("optionVerbose")) {
System.err.println("[Removing dead production " + p.qName + "]");
}
analyzer.remove((FullProduction)p);
iter.remove();
}
}
// Done.
return null;
}
/** Visit the specified nonterminal. */
public Element visit(NonTerminal nt) {
FullProduction p = analyzer.lookup(nt);
if (! analyzer.isMarked(p.qName)) {
analyzer.mark(p.qName);
dispatch(p);
}
return nt;
}
}