/*
* FindBugs - Find bugs in Java programs
* Copyright (C) 2004 Dave Brosius <dbrosius@users.sourceforge.net>
* Copyright (C) 2004 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 java.util.HashMap;
import java.util.Map;
import org.apache.bcel.classfile.Method;
import edu.umd.cs.findbugs.BugInstance;
import edu.umd.cs.findbugs.BugReporter;
import edu.umd.cs.findbugs.BytecodeScanningDetector;
import edu.umd.cs.findbugs.StatelessDetector;
import edu.umd.cs.findbugs.SystemProperties;
import edu.umd.cs.findbugs.visitclass.DismantleBytecode;
/**
* Find occurrences of using the String "+" or "+=" operators
* within a loop. This is much less efficient than creating
* a dedicated StringBuffer object outside the loop, and
* then appending to it.
*
* @author Dave Brosius
* @author William Pugh
*/
public class StringConcatenation extends BytecodeScanningDetector implements StatelessDetector {
private static final boolean DEBUG
= SystemProperties.getBoolean("sbsc.debug");
static final int SEEN_NOTHING = 0;
static final int SEEN_NEW = 1;
static final int SEEN_APPEND1 = 2;
static final int SEEN_APPEND2 = 3;
static final int CONSTRUCTED_STRING_ON_STACK = 4;
static final int POSSIBLE_CASE = 5;
private BugReporter bugReporter;
private boolean reportedThisMethod;
private int registerOnStack = -1;
private int stringSource = -1;
private int createPC = -1;
private int state = SEEN_NOTHING;
public StringConcatenation(BugReporter bugReporter) {
this.bugReporter = bugReporter;
}
// Keep track of which registers where clobbered at which PC, on
// a per-method basis
private Map<Integer,Integer> clobberedRegisters = new HashMap<Integer,Integer>();
@Override
public void visit(Method obj) {
if (DEBUG)
System.out.println("------------------- Analyzing " + obj.getName() + " ----------------");
reset();
clobberedRegisters = new HashMap<Integer,Integer>();
reportedThisMethod = false;
super.visit(obj);
}
private void reset() {
state = SEEN_NOTHING;
createPC = -1;
registerOnStack = -1;
stringSource = -1;
// For debugging: print what call to reset() is being invoked.
// This helps figure out why the detector is failing to
// recognize a particular idiom.
if (DEBUG) System.out.println("Reset from: " + new Throwable().getStackTrace()[1]);
}
private boolean storeIntoRegister(int seen, int reg) {
switch (seen) {
case ASTORE_0:
return reg == 0;
case ASTORE_1:
return reg == 1;
case ASTORE_2:
return reg == 2;
case ASTORE_3:
return reg == 3;
case ASTORE:
return reg == getRegisterOperand();
default:
return false;
}
}
@Override
public void sawOpcode(int seen) {
if (reportedThisMethod) return;
int oldState = state;
if (DEBUG) {
System.out.print("Opcode: ");
printOpCode(seen);
}
// Keep track of registers that are clobbered and at what PC,
// not including stores due to string concatenations
int storeTo = -1;
switch(seen) {
case ASTORE_0:
storeTo = 0;
break;
case ASTORE_1:
storeTo = 1;
break;
case ASTORE_2:
storeTo = 2;
break;
case ASTORE_3:
storeTo = 3;
break;
case ASTORE:
storeTo = getRegisterOperand();
break;
}
if(storeTo >= 0 && state != CONSTRUCTED_STRING_ON_STACK) {
clobberedRegisters.put(storeTo, getPC());
}
switch (state) {
case SEEN_NOTHING:
if ((seen == NEW)
&&
getClassConstantOperand().startsWith("java/lang/StringBu")) {
state = SEEN_NEW;
createPC = getPC();
}
break;
case SEEN_NEW:
if (seen == INVOKESPECIAL
&& "<init>".equals(getNameConstantOperand())
&& "(Ljava/lang/String;)V".equals(getSigConstantOperand())
&& getClassConstantOperand().startsWith("java/lang/StringBu")
&& registerOnStack >= 0) {
state = SEEN_APPEND1;
stringSource = registerOnStack;
} else if (seen == INVOKEVIRTUAL
&& "append".equals(getNameConstantOperand())
&& getClassConstantOperand().startsWith("java/lang/StringBu")) {
if (DEBUG) System.out.println("Saw string being appended from register " + registerOnStack);
if (getSigConstantOperand().startsWith("(Ljava/lang/String;)")
&& registerOnStack >= 0) {
if (DEBUG)
System.out.println("Saw string being appended, source = " + registerOnStack);
state = SEEN_APPEND1;
stringSource = registerOnStack;
} else
reset();
}
break;
case SEEN_APPEND1:
if (storeIntoRegister(seen, stringSource))
reset();
else if (seen == INVOKEVIRTUAL
&& "append".equals(getNameConstantOperand())
&& getClassConstantOperand().startsWith("java/lang/StringBu")) {
state = SEEN_APPEND2;
}
break;
case SEEN_APPEND2:
if (storeIntoRegister(seen, stringSource))
reset();
else if (seen == INVOKEVIRTUAL
&& "toString".equals(getNameConstantOperand())
&& getClassConstantOperand().startsWith("java/lang/StringBu")) {
state = CONSTRUCTED_STRING_ON_STACK;
}
break;
case CONSTRUCTED_STRING_ON_STACK:
if (storeIntoRegister(seen, stringSource))
state = POSSIBLE_CASE;
else
reset();
break;
case POSSIBLE_CASE:
// Note: the bottom of a loop is not necessarily a goto;
// one sourceforge bug (Bug1811106) pointed out that for
// do/while loops, it may be a if_icmpge. I generalized
// it to any branch.
if (DismantleBytecode.isBranch(seen)
&& (getPC() - getBranchTarget()) < 300
&& getBranchTarget() <= createPC) {
// Next check: was the destination register clobbered
// elsewhere in this loop?
boolean clobberedInLoop = false;
for(int reg : clobberedRegisters.keySet()) {
if(reg != stringSource) {
continue;
}
int pc = clobberedRegisters.get(reg);
if(pc >= getBranchTarget()) {
clobberedInLoop = true;
break;
}
}
if(clobberedInLoop) {
reset();
break;
}
bugReporter.reportBug(new BugInstance(this, "SBSC_USE_STRINGBUFFER_CONCATENATION", NORMAL_PRIORITY)
.addClassAndMethod(this)
.addSourceLine(this, createPC));
// System.out.println("SBSC spread: " + (getPC() - getBranchTarget()));
reset();
reportedThisMethod = true;
} else if ((seen == NEW)
&&
getClassConstantOperand().startsWith("java/lang/StringBu")) {
state = SEEN_NEW;
createPC = getPC();
} else {
if(DismantleBytecode.isBranch(seen) && DEBUG) {
System.out.println("Rejecting branch:");
System.out.println(" spread: " + (getPC() - getBranchTarget()));
System.out.println(" getBranchTarget(): " + getBranchTarget());
System.out.println(" createPC: " + createPC);
}
}
break;
}
if (seen == INVOKESTATIC && getNameConstantOperand().equals("valueOf") && getClassConstantOperand().equals("java/lang/String")
&& getSigConstantOperand().equals("(Ljava/lang/Object;)Ljava/lang/String;")) {
// leave registerOnStack unchanged
} else {
registerOnStack = -1;
switch (seen) {
case ALOAD_0:
registerOnStack = 0;
break;
case ALOAD_1:
registerOnStack = 1;
break;
case ALOAD_2:
registerOnStack = 2;
break;
case ALOAD_3:
registerOnStack = 3;
break;
case ALOAD:
registerOnStack = getRegisterOperand();
break;
}
}
if (DEBUG && state != oldState)
System.out.println("At PC " + getPC()
+ " changing from state " + oldState
+ " to state " + state
+ ", regOnStack = " + registerOnStack);
}
}
// vim:ts=4