FindBadForLoop.java

/*
 * FindBugs - Find bugs in Java programs
 * Copyright (C) 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.detect;

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

import edu.umd.cs.findbugs.BugInstance;
import edu.umd.cs.findbugs.BugReporter;
import edu.umd.cs.findbugs.OpcodeStack;
import edu.umd.cs.findbugs.StatelessDetector;
import edu.umd.cs.findbugs.bcel.OpcodeStackDetector;

public class FindBadForLoop extends OpcodeStackDetector implements StatelessDetector {

    BugReporter bugReporter;

    public FindBadForLoop(BugReporter bugReporter) {
        this.bugReporter = bugReporter;
    }

    LineNumberTable lineNumbers;

    @Override
    public void visit(Code obj) {
        lastRegStore = -1;
        lineNumbers = obj.getLineNumberTable();
        super.visit(obj);
    }

    int lastRegStore;

    @Override
    public void sawOpcode(int seen) {
        if (seen == ISTORE || seen == ISTORE_0 || seen == ISTORE_1 || seen == ISTORE_2 || seen == ISTORE_3)
            lastRegStore = getRegisterOperand();
        if (lineNumbers != null
                && stack.getStackDepth() >= 2
                && (seen == IF_ICMPGE || seen == IF_ICMPGT || seen == IF_ICMPLT || seen == IF_ICMPLE || seen == IF_ICMPNE || seen == IF_ICMPEQ)) {
            OpcodeStack.Item item0 = stack.getStackItem(0);
            OpcodeStack.Item item1 = stack.getStackItem(1);
            int r0 = item0.getRegisterNumber();
            int r1 = item1.getRegisterNumber();
            int rMin = Math.min(r0, r1);
            int rMax = Math.max(r0, r1);
            int branchTarget = getBranchTarget();
            if (rMin == -1 && rMax > 0 && rMax == lastRegStore && branchTarget - 6 > getPC()) {
                int beforeTarget = getCodeByte(branchTarget - 3);
                int beforeGoto = getCodeByte(branchTarget - 6);
                if (beforeTarget == GOTO && beforeGoto == IINC) {
                    int offset1 = (byte) getCodeByte(branchTarget - 2);
                    int offset2 = getCodeByte(branchTarget - 1);
                    int offset = offset1 << 8 | offset2;
                    int backTarget = branchTarget - 3 + offset;
                    int reg = getCodeByte(branchTarget - 5);
                    int testLineNumber = lineNumbers.getSourceLine(getPC());
                    int incLineNumber = lineNumbers.getSourceLine(branchTarget - 6);
                    int beforeIncLineNumber = lineNumbers.getSourceLine(branchTarget - 7);
                    if (backTarget < getPC() && getPC() - 8 < backTarget && reg != rMax && incLineNumber < testLineNumber + 3
                            && beforeIncLineNumber > incLineNumber) {

                        bugReporter.reportBug(new BugInstance(this, "QF_QUESTIONABLE_FOR_LOOP", NORMAL_PRIORITY)
                                .addClassAndMethod(this).addSourceLine(this));
                    }
                }

            }
        }
    }

}