com.thesett.aima.logic.fol.wam.optimizer.WAMOptimizer Maven / Gradle / Ivy

Go to download
/*
 * Copyright The Sett Ltd, 2005 to 2014.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.thesett.aima.logic.fol.wam.optimizer;

import java.util.List;

import com.thesett.aima.logic.fol.VariableAndFunctorInterner;
import com.thesett.aima.logic.fol.wam.compiler.WAMInstruction;
import com.thesett.aima.logic.fol.wam.compiler.WAMOptimizeableListing;
import com.thesett.common.util.SizeableLinkedList;
import com.thesett.common.util.SizeableList;
import com.thesett.common.util.doublemaps.SymbolTable;

/**
 * WAMOptimizer performs peephole optimization on a list of WAM instructions.
 *
 * 
 * CRC Card Responsibilities  Collaborations
 * 
 Optimize a WAM instruction listing.
 * 
 *
 * @author Rupert Smith
 */
public class WAMOptimizer implements Optimizer
{
    /** The symbol table. */
    protected final SymbolTable symbolTable;

    /** Holds the variable and functor name interner for the machine. */
    private final VariableAndFunctorInterner interner;

    /**
     * Builds a WAM instruction optimizer.
     *
     * @param symbolTable The symbol table to get instruction analysis information from.
     * @param interner    The variable and functor name interner for the machine.
     */
    public WAMOptimizer(SymbolTable symbolTable, VariableAndFunctorInterner interner)
    {
        this.symbolTable = symbolTable;
        this.interner = interner;
    }

    /**
     * {@inheritDoc}
     *
     * Runs the instruction listing through an optimizer pass, and replaces the original instruction listing with
     * the optimized version.
     */
    public  T apply(WAMOptimizeableListing listing)
    {
        SizeableList optListing = optimize(listing.getInstructions());
        listing.setOptimizedInstructions(optListing);

        return (T) listing;
    }

    /**
     * Performs an optimization pass for specialized instructions.
     *
     * 
The following instruction sequences can be optimized:
     *
     * 
     * unify_var Xi, get_struc a/0, Xi -> unify_const a/0
     * get_struc a/0, Xi -> get_const a/0
     * put_struc a/0, Xi, set_var Xi -> set_const a/0
     * put_struc a/0, Xi -> put_const a/0
     * 
     *
     * @param  instructions The instructions to optimize.
     *
     * @return An list of optimized instructions.
     */
    private SizeableList optimize(List instructions)
    {
        StateMachine optimizeConstants = new OptimizeInstructions(symbolTable, interner);
        Matcher matcher =
            new Matcher(instructions.iterator(), optimizeConstants);

        SizeableList result = new SizeableLinkedList();

        for (WAMInstruction instruction : matcher)
        {
            result.add(instruction);
        }

        return result;
    }
}