/*
 * Bytecode Analysis Framework
 * Copyright (C) 2003,2004 University of Maryland
 *
 * This library 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

package edu.umd.cs.findbugs.ba.vna;

import java.util.BitSet;
import java.util.HashMap;
import java.util.IdentityHashMap;
import java.util.Iterator;

import javax.annotation.CheckForNull;

import org.apache.bcel.generic.InstructionHandle;
import org.apache.bcel.generic.MethodGen;

import edu.umd.cs.findbugs.SystemProperties;
import edu.umd.cs.findbugs.ba.BasicBlock;
import edu.umd.cs.findbugs.ba.Dataflow;
import edu.umd.cs.findbugs.ba.DataflowAnalysisException;
import edu.umd.cs.findbugs.ba.DepthFirstSearch;
import edu.umd.cs.findbugs.ba.Edge;
import edu.umd.cs.findbugs.ba.FrameDataflowAnalysis;
import edu.umd.cs.findbugs.ba.Location;
import edu.umd.cs.findbugs.ba.RepositoryLookupFailureCallback;
import edu.umd.cs.findbugs.internalAnnotations.DottedClassName;

/**
 * A dataflow analysis to track the production and flow of values in the Java
 * stack frame. See the {@link ValueNumber ValueNumber} class for an explanation
 * of what the value numbers mean, and when they can be compared.
 *
 * <p>
 * This class is still experimental.
 *
 * @author David Hovemeyer
 * @see ValueNumber
 * @see edu.umd.cs.findbugs.ba.DominatorsAnalysis
 */
public class ValueNumberAnalysis extends FrameDataflowAnalysis<ValueNumber, ValueNumberFrame> {

    private final static boolean TRACE =  SystemProperties.getBoolean("vna.trace");

    public static final boolean DEBUG = TRACE || SystemProperties.getBoolean("vna.debug");

    private final MethodGen methodGen;

    private final ValueNumberFactory factory;

    private final ValueNumberFrameModelingVisitor visitor;

    private final ValueNumber[] entryLocalValueList;

    private final IdentityHashMap<BasicBlock, ValueNumber> exceptionHandlerValueNumberMap;

    private ValueNumber thisValue;

    private final HashMap<Location, ValueNumberFrame> factAtLocationMap;

    private final HashMap<Location, ValueNumberFrame> factAfterLocationMap;

    private MergeTree mergeTree;

    public ValueNumberAnalysis(MethodGen methodGen, DepthFirstSearch dfs, LoadedFieldSet loadedFieldSet,
            RepositoryLookupFailureCallback lookupFailureCallback) {

        super(dfs);
        this.methodGen = methodGen;
        this.factory = new ValueNumberFactory();
        ValueNumberCache cache = new ValueNumberCache();
        this.visitor = new ValueNumberFrameModelingVisitor(methodGen, factory, cache, loadedFieldSet, lookupFailureCallback);

        int numLocals = methodGen.getMaxLocals();
        this.entryLocalValueList = new ValueNumber[numLocals];
        for (int i = 0; i < numLocals; ++i)
            this.entryLocalValueList[i] = factory.createFreshValue();

        this.exceptionHandlerValueNumberMap = new IdentityHashMap<BasicBlock, ValueNumber>();

        // For non-static methods, keep track of which value represents the
        // "this" reference
        if (!methodGen.isStatic())
            this.thisValue = entryLocalValueList[0];

        this.factAtLocationMap = new HashMap<Location, ValueNumberFrame>();
        this.factAfterLocationMap = new HashMap<Location, ValueNumberFrame>();
        if (DEBUG)
            System.out.println("VNA Analysis " + methodGen.getClassName() + "." + methodGen.getName() + " : "
                    + methodGen.getSignature());

    }

    public ValueNumber getClassObjectValue(String className) {
        return visitor.factory.getClassObjectValue(className);
    }

    public void setMergeTree(MergeTree mergeTree) {
        this.mergeTree = mergeTree;
    }

    public MergeTree getMergeTree() {
        return mergeTree;
    }

    public ValueNumberFactory getFactory() {
        return factory;
    }

    public int getNumValuesAllocated() {
        return factory.getNumValuesAllocated();
    }

    public boolean isThisValue(ValueNumber value) {
        return thisValue != null && thisValue.getNumber() == value.getNumber();
    }

    public ValueNumber getThisValue() {
        return thisValue;
    }

    /**
     * Get the value number assigned to the given local variable upon entry to
     * the method.
     *
     * @param local
     *            local variable number
     * @return ValueNumber assigned to the local variable
     */
    public ValueNumber getEntryValue(int local) {
        return entryLocalValueList[local];
    }

    /**
     * Get the value number assigned to the given parameter upon entry to the
     * method.
     *
     * @param param
     *            a parameter (0 == first parameter)
     * @return the ValueNumber assigned to that parameter
     */
    public ValueNumber getEntryValueForParameter(int param) {
        return getEntryValue(methodGen.isStatic() ? param : param + 1);
    }

    public ValueNumberFrame createFact() {
        return new ValueNumberFrame(methodGen.getMaxLocals());
    }

    public void initEntryFact(ValueNumberFrame result) {
        // Change the frame from TOP to something valid.
        result.setValid();

        // At entry to the method, each local has (as far as we know) a unique
        // value.
        int numSlots = result.getNumSlots();
        for (int i = 0; i < numSlots; ++i)
            result.setValue(i, entryLocalValueList[i]);
    }

    @Override
    public void transferInstruction(InstructionHandle handle, BasicBlock basicBlock, ValueNumberFrame fact)
            throws DataflowAnalysisException {

        Location location = new Location(handle, basicBlock);

        ValueNumberFrame atLocation = getFactAtLocation(location);
        copy(fact, atLocation);

        visitor.setFrameAndLocation(fact, new Location(handle, basicBlock));
        visitor.setHandle(handle);
        visitor.analyzeInstruction(handle.getInstruction());

        ValueNumberFrame afterLocation = getFactAfterLocation(location);
        copy(fact, afterLocation);
    }

    public void meetInto(ValueNumberFrame fact, Edge edge, ValueNumberFrame result) throws DataflowAnalysisException {
        if (edge.getTarget().isExceptionHandler() && fact.isValid()) {
            // Special case: when merging predecessor facts for entry to
            // an exception handler, we clear the stack and push a
            // single entry for the exception object. That way, the locals
            // can still be merged.

            // Get the value number for the exception
            BasicBlock handlerBlock = edge.getTarget();
            ValueNumber exceptionValueNumber = getExceptionValueNumber(handlerBlock);

            // Set up the stack frame
            ValueNumberFrame tmpFact = createFact();
            tmpFact.copyFrom(fact);
            tmpFact.clearStack();
            tmpFact.pushValue(exceptionValueNumber);
            fact = tmpFact;
        }

        mergeInto(fact, result);
    }

    @Override
    protected void mergeInto(ValueNumberFrame frame, ValueNumberFrame result) throws DataflowAnalysisException {
        result.mergeAvailableLoadSets(frame, factory, mergeTree);
        super.mergeInto(frame, result);
    }

    @Override
    protected void mergeValues(ValueNumberFrame otherFrame, ValueNumberFrame resultFrame, int slot)
            throws DataflowAnalysisException {
        ValueNumber value = mergeValues(resultFrame, slot, resultFrame.getValue(slot), otherFrame.getValue(slot));
        resultFrame.setValue(slot, value);
    }

    private ValueNumber mergeValues(ValueNumberFrame frame, int slot, ValueNumber mine, ValueNumber other)
             {

        // Merging slot values:
        // - Merging identical values results in no change
        // - If the values are different, and the value in the result
        // frame is not the result of a previous result, a fresh value
        // is allocated.
        // - If the value in the result frame is the result of a
        // previous merge, IT STAYS THE SAME.
        //
        // The "one merge" rule means that merged values are essentially like
        // phi nodes. They combine some number of other values.

        // I believe (but haven't proved) that this technique is a dumb way
        // of computing SSA.

        if (mine != frame.getValue(slot))
            throw new IllegalStateException();

        if (mine.equals(other))
            return mine;

        ValueNumber mergedValue = frame.getMergedValue(slot);
        if (mergedValue == null) {
            mergedValue = factory.createFreshValue(ValueNumber.mergeFlags(mine.getFlags(), other.getFlags()) | ValueNumber.PHI_NODE);
            frame.setMergedValue(slot, mergedValue);

        }

        if (mergeTree != null) {
            mergeTree.mapInputToOutput(mine, mergedValue);
            mergeTree.mapInputToOutput(other, mergedValue);
        }

        return mergedValue;
    }

    @Override
    public ValueNumberFrame getFactAtLocation(Location location) {
        ValueNumberFrame fact = factAtLocationMap.get(location);
        if (fact == null) {
            fact = createFact();
            makeFactTop(fact);
            factAtLocationMap.put(location, fact);
        }
        return fact;
    }


    @Override
    public ValueNumberFrame getFactAfterLocation(Location location) {
        if (TRACE)
            System.out.println("getting fact after " + location);
        ValueNumberFrame fact = factAfterLocationMap.get(location);
        if (fact == null) {
            if (TRACE)
                System.out
                        .println("Initialized fact after " + location + " @ "
                                + Integer.toHexString(System.identityHashCode(location)) + " in "
                                + Integer.toHexString(System.identityHashCode(this)) + " : "
                                + factAfterLocationMap.containsKey(location));

            fact = createFact();
            makeFactTop(fact);
            factAfterLocationMap.put(location, fact);
        }
        return fact;
    }

    /**
     * Get an Iterator over all dataflow facts that we've recorded for the
     * Locations in the CFG. Note that this does not include result facts (since
     * there are no Locations corresponding to the end of basic blocks).
     */
    public Iterator<ValueNumberFrame> factIterator() {
        return factAtLocationMap.values().iterator();
    }

    // These fields are used by the compactValueNumbers() method.
    private static class ValueCompacter {
        public final BitSet valuesUsed;

        public int numValuesUsed;

        public final int[] discovered;

        public ValueCompacter(int origNumValuesAllocated) {
            valuesUsed = new BitSet();
            numValuesUsed = 0;

            // The "discovered" array tells us the mapping of old value numbers
            // to new (which are based on order of discovery). Negative values
            // specify value numbers which are not actually used (and thus can
            // be purged.)
            discovered = new int[origNumValuesAllocated];
            for (int i = 0; i < discovered.length; ++i)
                discovered[i] = -1;
        }

        public boolean isUsed(int number) {
            return valuesUsed.get(number);
        }

        public void setUsed(int number) {
            valuesUsed.set(number, true);
        }

        public int allocateValue() {
            return numValuesUsed++;
        }
    }

    /**
     * Compact the value numbers assigned. This should be done only after the
     * dataflow algorithm has executed. This works by modifying the actual
     * ValueNumber objects assigned. After this method is called, the
     * getNumValuesAllocated() method of this object will return a value less
     * than or equal to the value it would have returned before the call to this
     * method.
     * <p/>
     * <p>
     * <em>This method should be called at most once</em>.
     *
     * @param dataflow
     *            the Dataflow object which executed this analysis (and has all
     *            of the block result values)
     */
    @Deprecated
    public void compactValueNumbers(Dataflow<ValueNumberFrame, ValueNumberAnalysis> dataflow) {
        if (true)
            throw new UnsupportedOperationException();
        ValueCompacter compacter = new ValueCompacter(factory.getNumValuesAllocated());

        // We can get all extant Frames by looking at the values in
        // the location to value map, and also the block result values.
        for (Iterator<ValueNumberFrame> i = factIterator(); i.hasNext();) {
            ValueNumberFrame frame = i.next();
            markFrameValues(frame, compacter);
        }
        for (Iterator<ValueNumberFrame> i = resultFactIterator(); i.hasNext();) {
            ValueNumberFrame frame = i.next();
            markFrameValues(frame, compacter);
        }

        int before = factory.getNumValuesAllocated();

        // Now the factory can modify the ValueNumbers.
        factory.compact(compacter.discovered, compacter.numValuesUsed);

        int after = factory.getNumValuesAllocated();

        if (DEBUG && after < before && before > 0)
            System.out.println("Value compaction: " + after + "/" + before + " (" + ((after * 100) / before) + "%)");

    }

    /**
     * Mark value numbers in a value number frame for compaction.
     */
    private static void markFrameValues(ValueNumberFrame frame, ValueCompacter compacter) {
        // We don't need to do anything for top and bottom frames.
        if (!frame.isValid())
            return;

        for (int j = 0; j < frame.getNumSlots(); ++j) {
            ValueNumber value = frame.getValue(j);
            int number = value.getNumber();

            if (!compacter.isUsed(number)) {
                compacter.discovered[number] = compacter.allocateValue();
                compacter.setUsed(number);
            }
        }
    }

    // /**
    // * Test driver.
    // */
    // public static void main(String[] argv) throws Exception {
    //
    // if (argv.length != 1) {
    // System.out.println("Usage: edu.umd.cs.findbugs.ba.ValueNumberAnalysis <filename>");
    // System.exit(1);
    // }
    //
    // DataflowTestDriver<ValueNumberFrame, ValueNumberAnalysis> driver =
    // new DataflowTestDriver<ValueNumberFrame, ValueNumberAnalysis>() {
    // @Override
    // public Dataflow<ValueNumberFrame, ValueNumberAnalysis>
    // createDataflow(ClassContext classContext, Method method)
    // throws CFGBuilderException, DataflowAnalysisException {
    // return classContext.getValueNumberDataflow(method);
    // }
    // };
    //
    // driver.execute(argv[0]);
    // }

    private ValueNumber getExceptionValueNumber(BasicBlock handlerBlock) {
        ValueNumber valueNumber = exceptionHandlerValueNumberMap.get(handlerBlock);
        if (valueNumber == null) {
            valueNumber = factory.createFreshValue();
            exceptionHandlerValueNumberMap.put(handlerBlock, valueNumber);
        }
        return valueNumber;
    }

    public @CheckForNull
    @DottedClassName
    String getClassName(ValueNumber v) {
        return factory.getClassName(v);
    }
}

// vim:ts=4
