/*
* 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 java.util.BitSet;
import org.apache.bcel.Constants;
import org.apache.bcel.classfile.Code;
import org.apache.bcel.classfile.CodeException;
import com.mebigfatguy.fbcontrib.utils.AttributesUtils;
import com.mebigfatguy.fbcontrib.utils.BugType;
import com.mebigfatguy.fbcontrib.utils.RegisterUtils;
import com.mebigfatguy.fbcontrib.utils.TernaryPatcher;
import com.mebigfatguy.fbcontrib.utils.Values;
import edu.umd.cs.findbugs.BugInstance;
import edu.umd.cs.findbugs.BugReporter;
import edu.umd.cs.findbugs.BytecodeScanningDetector;
import edu.umd.cs.findbugs.OpcodeStack;
import edu.umd.cs.findbugs.OpcodeStack.CustomUserValue;
import edu.umd.cs.findbugs.ba.ClassContext;
/**
* looks for construction of new objects, and then the immediate testing whether the object is null or not. As the new operator will always succeed, or through
* an exception, this test is unnecessary and represents a misunderstanding as to how the jvm works.
*/
@CustomUserValue
public class UnnecessaryNewNullCheck extends BytecodeScanningDetector {
private final BugReporter bugReporter;
private OpcodeStack stack;
private BitSet allocationRegs;
private BitSet transitionPoints;
public UnnecessaryNewNullCheck(BugReporter bugReporter) {
this.bugReporter = bugReporter;
}
@Override
public void visitClassContext(ClassContext classContext) {
try {
stack = new OpcodeStack();
allocationRegs = new BitSet();
transitionPoints = new BitSet();
super.visitClassContext(classContext);
} finally {
stack = null;
allocationRegs = null;
transitionPoints = null;
}
}
@Override
public void visitCode(Code obj) {
if (prescreen()) {
stack.resetForMethodEntry(this);
allocationRegs.clear();
transitionPoints.clear();
CodeException[] ce = obj.getExceptionTable();
if (ce != null) {
for (CodeException element : ce) {
transitionPoints.set(element.getEndPC());
}
}
super.visitCode(obj);
}
}
@Override
public void sawOpcode(int seen) {
boolean sawAlloc = false;
try {
stack.precomputation(this);
if (transitionPoints.get(getPC())) {
allocationRegs.clear();
int depth = stack.getStackDepth();
for (int i = 0; i < depth; i++) {
OpcodeStack.Item item = stack.getStackItem(i);
item.setUserValue(null);
}
}
switch (seen) {
case NEW:
case ANEWARRAY:
case MULTIANEWARRAY:
sawAlloc = true;
break;
case INVOKESPECIAL:
if (Values.CONSTRUCTOR.equals(getNameConstantOperand())) {
sawAlloc = true;
}
break;
case ASTORE:
case ASTORE_0:
case ASTORE_1:
case ASTORE_2:
case ASTORE_3:
if (stack.getStackDepth() > 0) {
OpcodeStack.Item item = stack.getStackItem(0);
int reg = RegisterUtils.getAStoreReg(this, seen);
if (item.getUserValue() == null) {
allocationRegs.clear(reg);
} else {
allocationRegs.set(reg);
}
}
break;
case ALOAD:
case ALOAD_0:
case ALOAD_1:
case ALOAD_2:
case ALOAD_3:
int reg = RegisterUtils.getALoadReg(this, seen);
sawAlloc = (allocationRegs.get(reg));
break;
case IFNONNULL:
case IFNULL:
if (stack.getStackDepth() > 0) {
OpcodeStack.Item item = stack.getStackItem(0);
if ((item.getUserValue() != null) && AttributesUtils.isValidLineNumber(getCode(), getPC())) {
bugReporter.reportBug(new BugInstance(this, BugType.UNNC_UNNECESSARY_NEW_NULL_CHECK.name(), NORMAL_PRIORITY).addClass(this)
.addMethod(this).addSourceLine(this));
}
}
transitionPoints.set(getBranchTarget());
allocationRegs.clear();
break;
case IFEQ:
case IFNE:
case IFLT:
case IFGE:
case IFGT:
case IFLE:
case IF_ICMPEQ:
case IF_ICMPNE:
case IF_ICMPLT:
case IF_ICMPGE:
case IF_ICMPGT:
case IF_ICMPLE:
case IF_ACMPEQ:
case IF_ACMPNE:
case GOTO:
case GOTO_W:
transitionPoints.set(getBranchTarget());
allocationRegs.clear();
break;
case TABLESWITCH:
case LOOKUPSWITCH:
case IRETURN:
case LRETURN:
case FRETURN:
case DRETURN:
case ARETURN:
case RETURN:
case ATHROW:
allocationRegs.clear();
break;
default:
break;
}
} finally {
TernaryPatcher.pre(stack, seen);
stack.sawOpcode(this, seen);
TernaryPatcher.post(stack, seen);
if (stack.getStackDepth() > 0) {
OpcodeStack.Item item = stack.getStackItem(0);
item.setUserValue(sawAlloc ? Boolean.TRUE : null);
}
}
}
private boolean prescreen() {
BitSet bytecodeSet = getClassContext().getBytecodeSet(getMethod());
return (bytecodeSet != null) && (bytecodeSet.get(Constants.NEW) || bytecodeSet.get(Constants.ANEWARRAY) || bytecodeSet.get(Constants.MULTIANEWARRAY));
}
}