/* Copyright (c) 2002-2011 by XMLVM.org
*
* Project Info: http://www.xmlvm.org
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or
* (at your option) any later version.
*
* This library 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 Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
* USA.
*/
package org.xmlvm.refcount.optimizations;
import java.util.List;
import java.util.Map;
import org.jdom.DataConversionException;
import org.jdom.Element;
import org.xmlvm.refcount.CodePath;
import org.xmlvm.refcount.InstructionActions;
import org.xmlvm.refcount.InstructionUseInfo;
import org.xmlvm.refcount.OnePathInstructionRegisterContents;
import org.xmlvm.refcount.ReferenceCountingException;
import org.xmlvm.refcount.RegisterSet;
/**
* Used to defer nulling of registers until the last second. This allows us to
* not null as often because writes of other values clear the need to null out a
* register.
*/
public class DeferredNullingOptimization implements RefCountOptimization
{
public ReturnValue Process(List<CodePath> allCodePaths, Map<Element, InstructionActions> beenTo, Element codeElement) throws ReferenceCountingException, DataConversionException
{
ReturnValue toRet= new ReturnValue();
RegisterSet allRegs= new RegisterSet();
for (CodePath curPath : allCodePaths)
{
for (OnePathInstructionRegisterContents curInst : curPath.path)
{
InstructionUseInfo useInfo= beenTo.get(curInst.instruction).useInfo;
allRegs.orEq(useInfo.allWrites());
allRegs.orEq(useInfo.usedReg());
}
}
for (CodePath c : allCodePaths)
{
// We start with as early as possible nulls. Now we switch to
// as late as possible to prevent excess nulling
RegisterSet needsNull= RegisterSet.none();
InstructionActions act= null;
OnePathInstructionRegisterContents last= null;
for (OnePathInstructionRegisterContents curInst : c.path)
{
last= curInst;
act= beenTo.get(curInst.instruction);
needsNull.orEq(act.useInfo.willNull);
act.useInfo.willNull= RegisterSet.none();
needsNull.andEqNot(act.useInfo.allWrites());
}
if (act != null)
{
if (last.instruction.getName().startsWith("return"))
{
act.useInfo.willNull= RegisterSet.none();
}
else
{
act.useInfo.willNull.orEq(needsNull);
}
}
}
return toRet;
}
}