ResourceValueAnalysis.java

/*
 * Bytecode Analysis Framework
 * Copyright (C) 2003-2005 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;

import org.apache.bcel.Const;
import org.apache.bcel.generic.IFNONNULL;
import org.apache.bcel.generic.IFNULL;
import org.apache.bcel.generic.IF_ACMPEQ;
import org.apache.bcel.generic.IF_ACMPNE;
import org.apache.bcel.generic.Instruction;
import org.apache.bcel.generic.InstructionHandle;
import org.apache.bcel.generic.MethodGen;

import edu.umd.cs.findbugs.SystemProperties;

@javax.annotation.ParametersAreNonnullByDefault
public class ResourceValueAnalysis<Resource> extends FrameDataflowAnalysis<ResourceValue, ResourceValueFrame> implements
        EdgeTypes {

    private static final boolean DEBUG = SystemProperties.getBoolean("dataflow.debug");

    private final MethodGen methodGen;

    private final CFG cfg;

    private final ResourceTracker<Resource> resourceTracker;

    private final Resource resource;

    private final ResourceValueFrameModelingVisitor visitor;

    private final boolean ignoreImplicitExceptions;

    public ResourceValueAnalysis(MethodGen methodGen, CFG cfg, DepthFirstSearch dfs, ResourceTracker<Resource> resourceTracker,
            Resource resource) {

        super(dfs);
        this.methodGen = methodGen;
        this.cfg = cfg;
        this.resourceTracker = resourceTracker;
        this.resource = resource;
        this.visitor = resourceTracker.createVisitor(resource, methodGen.getConstantPool());

        this.ignoreImplicitExceptions = resourceTracker.ignoreImplicitExceptions(resource);
    }

    @Override
    public ResourceValueFrame createFact() {
        ResourceValueFrame fact = new ResourceValueFrame(methodGen.getMaxLocals());
        fact.setTop();
        return fact;
    }

    @Override
    public void initEntryFact(ResourceValueFrame result) {
        result.setValid();
        result.clearStack();
        final int numSlots = result.getNumSlots();
        for (int i = 0; i < numSlots; ++i) {
            boolean slotContainsInstance = resourceTracker.isParamInstance(resource, i);
            result.setValue(i, slotContainsInstance ? ResourceValue.instance() : ResourceValue.notInstance());
        }
    }

    @Override
    public void meetInto(ResourceValueFrame fact, Edge edge, ResourceValueFrame result) throws DataflowAnalysisException {
        BasicBlock source = edge.getSource();
        BasicBlock dest = edge.getTarget();

        ResourceValueFrame tmpFact = null;

        if (edge.isExceptionEdge()) {
            // If this edge throws only implicit exceptions
            // (as determined by TypeAnalysis and
            // PruneInfeasibleExceptionEdges),
            // and the resource tracker says to ignore implicit exceptions
            // for this resource, ignore it.
            if (AnalysisContext.currentAnalysisContext().getBoolProperty(AnalysisFeatures.ACCURATE_EXCEPTIONS)
                    && ignoreImplicitExceptions && !edge.isFlagSet(EXPLICIT_EXCEPTIONS_FLAG)) {
                return;
            }

            // The ResourceTracker may veto the exception edge
            if (resourceTracker.ignoreExceptionEdge(edge, resource, methodGen.getConstantPool())) {
                return;
            }

            if (fact.getStatus() == ResourceValueFrame.State.OPEN) {
                // If status is OPEN, downgrade to OPEN_ON_EXCEPTION_PATH
                tmpFact = modifyFrame(fact, null);
                tmpFact.setStatus(ResourceValueFrame.State.OPEN_ON_EXCEPTION_PATH);
            }

            if (fact.isValid()) {
                // Special case: if the instruction that closes the resource
                // throws an exception, we consider the resource to be
                // successfully
                // closed anyway.
                InstructionHandle exceptionThrower = source.getExceptionThrower();
                BasicBlock fallThroughSuccessor = cfg.getSuccessorWithEdgeType(source, FALL_THROUGH_EDGE);
                if (DEBUG && fallThroughSuccessor == null) {
                    System.out.println("Null fall through successor!");
                }
                if (fallThroughSuccessor != null
                        && resourceTracker.isResourceClose(fallThroughSuccessor, exceptionThrower, methodGen.getConstantPool(),
                                resource, fact)) {
                    tmpFact = modifyFrame(fact, tmpFact);
                    tmpFact.setStatus(ResourceValueFrame.State.CLOSED);
                    if (DEBUG) {
                        System.out.print("(failed attempt to close)");
                    }
                }
            }

            if (dest.isExceptionHandler()) {
                // Clear stack, push value for exception
                if (fact.isValid()) {
                    tmpFact = modifyFrame(fact, tmpFact);
                    tmpFact.clearStack();
                    tmpFact.pushValue(ResourceValue.notInstance());
                }
            }
        }

        // Make the resource nonexistent if it is compared against null
        int edgeType = edge.getType();
        if (edgeType == IFCMP_EDGE || edgeType == FALL_THROUGH_EDGE) {
            InstructionHandle lastInSourceHandle = source.getLastInstruction();
            if (lastInSourceHandle != null) {
                Instruction lastInSource = lastInSourceHandle.getInstruction();
                boolean isNullCheck = false;
                boolean isNonNullCheck = false;
                // This check catches null == X, null != X
                if (lastInSource instanceof IF_ACMPEQ || lastInSource instanceof IF_ACMPNE) {
                    Location l = new Location(lastInSourceHandle, source);
                    InstructionHandle ih = l.getHandle();
                    // Get instruction that pushed topmost
                    InstructionHandle ihPrev = ih.getPrev();
                    // Get next-topmost that pushed next-topmost
                    InstructionHandle ihPrevPrev = ihPrev == null ? null : ihPrev.getPrev();
                    int prevPush = 0;
                    if (ihPrev != null) {
                        prevPush = ihPrev.getInstruction().produceStack(methodGen.getConstantPool());
                    }
                    int prevPrevPush = 0;
                    if (ihPrevPrev != null) {
                        prevPrevPush = ihPrevPrev.getInstruction().produceStack(methodGen.getConstantPool());
                    }
                    // If instructions exist and both push one word onto the
                    // stack and the next-topmost pushes null...
                    if (ihPrev != null && ihPrevPrev != null && prevPush == 1 && prevPrevPush == 1
                            && ihPrevPrev.getInstruction().getOpcode() == Const.ACONST_NULL) {
                        // Topmost item on stack is being compared with null
                        // (the null itself is next-topmost on the stack)
                        isNullCheck = lastInSource instanceof IF_ACMPEQ;
                        isNonNullCheck = lastInSource instanceof IF_ACMPNE;
                    }
                }
                // This check catches X == null, X != null
                else if (lastInSource instanceof IFNULL || lastInSource instanceof IFNONNULL) {
                    isNullCheck = lastInSource instanceof IFNULL;
                    isNonNullCheck = lastInSource instanceof IFNONNULL;
                }
                if (isNullCheck || isNonNullCheck) {
                    // Get the frame at the if statement
                    ResourceValueFrame startFrame = getStartFact(source);
                    if (startFrame.isValid()) {
                        // The source block has a valid start fact.
                        // That means it is safe to inspect the frame at the If
                        // instruction.
                        ResourceValueFrame frameAtIf = getFactAtLocation(new Location(lastInSourceHandle, source));
                        ResourceValue topValue = frameAtIf.getValue(frameAtIf.getNumSlots() - 1);

                        if (topValue.isInstance()) {
                            if ((isNullCheck && edgeType == IFCMP_EDGE) || (isNonNullCheck && edgeType == FALL_THROUGH_EDGE)) {
                                // System.out.println("**** making resource nonexistent on edge "+edge.getId());
                                tmpFact = modifyFrame(fact, tmpFact);
                                tmpFact.setStatus(ResourceValueFrame.State.NONEXISTENT);
                            }
                        }
                    }
                }
            }
        }

        if (tmpFact != null) {
            fact = tmpFact;
        }

        mergeInto(fact, result);
    }

    @Override
    protected void mergeInto(ResourceValueFrame frame, ResourceValueFrame result) throws DataflowAnalysisException {
        // Merge slots
        super.mergeInto(frame, result);

        // Merge status
        result.setStatus(result.getStatus().getType() > frame.getStatus().getType() ? frame.getStatus() : result.getStatus());
    }

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

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

        visitor.setFrameAndLocation(fact, new Location(handle, basicBlock));
        visitor.transferInstruction(handle, basicBlock);

    }

}