NeedlessInstanceRetrieval.java

/*
 * fb-contrib - Auxiliary detectors for Java programs
 * Copyright (C) 2005-2017 Dave Brosius
 *
 * 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 com.mebigfatguy.fbcontrib.detect;

import org.apache.bcel.classfile.Code;
import org.apache.bcel.classfile.LineNumberTable;

import com.mebigfatguy.fbcontrib.utils.BugType;
import com.mebigfatguy.fbcontrib.utils.SignatureUtils;
import com.mebigfatguy.fbcontrib.utils.Values;

import edu.umd.cs.findbugs.BugInstance;
import edu.umd.cs.findbugs.BugReporter;
import edu.umd.cs.findbugs.BytecodeScanningDetector;

/**
 * looks for methods that call a method to retrieve a reference to an object, to use to load a constant. It is simpler and more performant to access the static
 * variable directly from the class itself.
 */
public class NeedlessInstanceRetrieval extends BytecodeScanningDetector {
    enum State {
        SEEN_NOTHING, SEEN_INVOKE, SEEN_POP
    }

    private final BugReporter bugReporter;
    private LineNumberTable lnTable;
    private State state;
    private int invokePC;
    private String returnType;

    /**
     * constructs a NIR detector given the reporter to report bugs on
     *
     * @param bugReporter
     *            the sync of bug reports
     */
    public NeedlessInstanceRetrieval(BugReporter bugReporter) {
        this.bugReporter = bugReporter;
    }

    /**
     * overrides the interface to collect the line number table, and reset state
     *
     * @param obj
     *            the content object of the currently parsed code
     */
    @Override
    public void visitCode(Code obj) {
        try {
            lnTable = obj.getLineNumberTable();
            if (lnTable != null) {
                state = State.SEEN_NOTHING;
                invokePC = -1;
                returnType = null;
                super.visitCode(obj);
            }
        } finally {
            lnTable = null;
        }
    }

    /**
     * overrides the interface to find accesses of static variables off of an instance immediately fetched from a method call.
     *
     * @param seen
     *            the opcode of the currently visited instruction
     */
    @Override
    public void sawOpcode(int seen) {
        switch (state) {
            case SEEN_NOTHING:
                if ((seen == INVOKEINTERFACE) || (seen == INVOKEVIRTUAL)) {
                    String sig = getSigConstantOperand();
                    String returnSig = SignatureUtils.getReturnSignature(sig);
                    if (returnSig.startsWith(Values.SIG_QUALIFIED_CLASS_PREFIX)) {
                        String clsName = getClassConstantOperand();
                        if (!Values.SLASHED_JAVA_LANG_OBJECT.equals(clsName) && !Values.SLASHED_JAVA_LANG_CLASS.equals(clsName)) {
                            returnType = SignatureUtils.trimSignature(returnSig);
                            invokePC = getPC();
                            state = State.SEEN_INVOKE;
                        }
                    }
                }
            break;

            case SEEN_INVOKE:
                if (seen == POP) {
                    state = State.SEEN_POP;
                } else {
                    state = State.SEEN_NOTHING;
                    returnType = null;
                }
            break;

            case SEEN_POP:
                if (((seen >= ACONST_NULL) && (seen <= DCONST_1)) || (seen == GETFIELD)) {
                    state = State.SEEN_POP;
                } else if ((seen == INVOKESTATIC) || (seen == GETSTATIC)) {
                    if (getClassConstantOperand().equals(returnType) && (lnTable.getSourceLine(invokePC) == lnTable.getSourceLine(getPC()))) {
                        bugReporter.reportBug(new BugInstance(this, BugType.NIR_NEEDLESS_INSTANCE_RETRIEVAL.name(), NORMAL_PRIORITY).addClass(this)
                                .addMethod(this).addSourceLine(this));
                    }
                    state = State.SEEN_NOTHING;
                    returnType = null;
                } else {
                    state = State.SEEN_NOTHING;
                    returnType = null;
                }
            break;

            default:
                state = State.SEEN_NOTHING;
                returnType = null;
            break;
        }
    }
}