LoadOfKnownNullValue.java

package edu.umd.cs.findbugs.detect;

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

import org.apache.bcel.classfile.LineNumberTable;
import org.apache.bcel.classfile.Method;
import org.apache.bcel.generic.ALOAD;
import org.apache.bcel.generic.ARETURN;
import org.apache.bcel.generic.BranchInstruction;
import org.apache.bcel.generic.GOTO;
import org.apache.bcel.generic.Instruction;
import org.apache.bcel.generic.InstructionHandle;
import org.apache.bcel.generic.MethodGen;

import edu.umd.cs.findbugs.BugAccumulator;
import edu.umd.cs.findbugs.BugInstance;
import edu.umd.cs.findbugs.BugReporter;
import edu.umd.cs.findbugs.Detector;
import edu.umd.cs.findbugs.SourceLineAnnotation;
import edu.umd.cs.findbugs.SystemProperties;
import edu.umd.cs.findbugs.ba.CFG;
import edu.umd.cs.findbugs.ba.CFGBuilderException;
import edu.umd.cs.findbugs.ba.ClassContext;
import edu.umd.cs.findbugs.ba.DataflowAnalysisException;
import edu.umd.cs.findbugs.ba.Location;
import edu.umd.cs.findbugs.ba.MethodUnprofitableException;
import edu.umd.cs.findbugs.ba.npe.IsNullValue;
import edu.umd.cs.findbugs.ba.npe.IsNullValueDataflow;
import edu.umd.cs.findbugs.ba.npe.IsNullValueFrame;

public class LoadOfKnownNullValue implements Detector {

	private BugReporter bugReporter;
	private BugAccumulator bugAccumulator;

	public LoadOfKnownNullValue(BugReporter bugReporter) {
		this.bugReporter = bugReporter;
		this.bugAccumulator = new BugAccumulator(bugReporter);
	}

	public void visitClassContext(ClassContext classContext) {
		Method[] methodList = classContext.getJavaClass().getMethods();

		for (Method method : methodList) {
			if (method.getCode() == null)
				continue;

			try {
				analyzeMethod(classContext, method);
			} catch (MethodUnprofitableException mue) {
				if (SystemProperties.getBoolean("unprofitable.debug")) // otherwise don't report
					bugReporter.logError("skipping unprofitable method in " + getClass().getName());
			} catch (CFGBuilderException e) {
				bugReporter.logError("Detector " + this.getClass().getName()
						+ " caught exception", e);
			} catch (DataflowAnalysisException e) {
				bugReporter.logError("Detector " + this.getClass().getName()
						+ " caught exception", e);
			}
			bugAccumulator.reportAccumulatedBugs();
		}
	}

	private void analyzeMethod(ClassContext classContext, Method method)
			throws CFGBuilderException, DataflowAnalysisException {
		BitSet lineMentionedMultipleTimes = ClassContext.linesMentionedMultipleTimes(method);
		BitSet linesWithLoadsOfNotDefinitelyNullValues = null;

		CFG cfg = classContext.getCFG(method);
		IsNullValueDataflow nullValueDataflow = classContext
				.getIsNullValueDataflow(method);
		MethodGen methodGen = classContext.getMethodGen(method);
		String sourceFile = classContext.getJavaClass().getSourceFileName();

		if (lineMentionedMultipleTimes.cardinality() > 0) {
			linesWithLoadsOfNotDefinitelyNullValues = new BitSet();
			LineNumberTable lineNumbers = method.getLineNumberTable();
			for (Iterator<Location> i = cfg.locationIterator(); i.hasNext();) {
				Location location = i.next();

				InstructionHandle handle = location.getHandle();
				Instruction ins = handle.getInstruction();
				if (!(ins instanceof ALOAD))
					continue;

				IsNullValueFrame frame = nullValueDataflow
						.getFactAtLocation(location);
				if (!frame.isValid()) {
					// This basic block is probably dead
					continue;
				}
				// System.out.println(handle.getPosition() + "\t" + ins.getName() +  "\t" + frame);

				ALOAD load = (ALOAD) ins;

				int index = load.getIndex();
				IsNullValue v = frame.getValue(index);
				if (!v.isDefinitelyNull()) {
					int sourceLine = lineNumbers.getSourceLine(handle.getPosition());
					if (sourceLine > 0)
					linesWithLoadsOfNotDefinitelyNullValues.set(sourceLine);
				}
		}
		}


		IdentityHashMap<InstructionHandle, Object> sometimesGood = new	IdentityHashMap<InstructionHandle, Object>();

		for (Iterator<Location> i = cfg.locationIterator(); i.hasNext();) {
			Location location = i.next();
			InstructionHandle handle = location.getHandle();
			Instruction ins = handle.getInstruction();
			if (!(ins instanceof ALOAD)) continue;
			IsNullValueFrame frame = nullValueDataflow.getFactAtLocation(location);
			if (!frame.isValid()) {
				// This basic block is probably dead
				continue;
			}
			// System.out.println(handle.getPosition() + "\t" + ins.getName() +  "\t" + frame);

			ALOAD load = (ALOAD) ins;

			int index = load.getIndex();
			IsNullValue v = frame.getValue(index);
			if (!v.isDefinitelyNull()) sometimesGood.put(handle, null);
		}

		// System.out.println(nullValueDataflow);
		for (Iterator<Location> i = cfg.locationIterator(); i.hasNext();) {
			Location location = i.next();

			InstructionHandle handle = location.getHandle();
			Instruction ins = handle.getInstruction();
			if (!(ins instanceof ALOAD))
				continue;

			if (sometimesGood.containsKey(handle)) continue;
			IsNullValueFrame frame = nullValueDataflow
					.getFactAtLocation(location);
			if (!frame.isValid()) {
				// This basic block is probably dead
				continue;
			}
			// System.out.println(handle.getPosition() + "\t" + ins.getName() +  "\t" + frame);

			ALOAD load = (ALOAD) ins;

			int index = load.getIndex();
			IsNullValue v = frame.getValue(index);
			if (v.isDefinitelyNull()) {
				Instruction next = handle.getNext().getInstruction();
				InstructionHandle prevHandle = handle.getPrev();
				SourceLineAnnotation sourceLineAnnotation = SourceLineAnnotation
				.fromVisitedInstruction(classContext, methodGen, sourceFile, handle);
				SourceLineAnnotation prevSourceLineAnnotation = SourceLineAnnotation
				.fromVisitedInstruction(classContext, methodGen, sourceFile, prevHandle);

				if (next instanceof ARETURN) {
					// probably stored for duration of finally block
					continue;
				}
				if(next instanceof GOTO) {
					InstructionHandle targ = ((BranchInstruction)next).getTarget();
					if(targ.getInstruction() instanceof ARETURN) {
						// Skip for the same reason we would skip if
						// (next instanceof ARETURN) were true.  This
						// is necessary because the bytecode compiler
						// compiles the ternary ? operator with a GOTO
						// to an ARETURN instead of just an ARETURN.
						continue;
					}
				}
				int startLine = sourceLineAnnotation.getStartLine();
				if (startLine > 0 && lineMentionedMultipleTimes.get(startLine) && linesWithLoadsOfNotDefinitelyNullValues.get(startLine))
					continue;

				int previousLine = prevSourceLineAnnotation.getEndLine();
				if (startLine < previousLine) {
					// probably stored for duration of finally block
					// System.out.println("Inverted line");
					continue;
				}
				int priority = NORMAL_PRIORITY;

				if (!v.isChecked()) priority++;
				// System.out.println("lineMentionedMultipleTimes: " + lineMentionedMultipleTimes);
				// System.out.println("linesWithLoadsOfNonNullValues: " + linesWithLoadsOfNotDefinitelyNullValues);

				bugAccumulator.accumulateBug(new BugInstance(this,
						"NP_LOAD_OF_KNOWN_NULL_VALUE",
						priority)
						.addClassAndMethod(methodGen, sourceFile),
						sourceLineAnnotation);
			}

		}
	}

	public void report() {
	}

}