org.aspectj/bcel-builder/verifier-src/org/aspectj/apache/bcel/verifier/structurals/ControlFlowGraph.java

package org.aspectj.apache.bcel.verifier.structurals;

/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2001 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (https://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation" and
 *    "Apache BCEL" must not be used to endorse or promote products
 *    derived from this software without prior written permission. For
 *    written permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache",
 *    "Apache BCEL", nor may "Apache" appear in their name, without
 *    prior written permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <https://www.apache.org/>.
 */

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Hashtable;

import org.aspectj.apache.bcel.Constants;
import org.aspectj.apache.bcel.generic.Instruction;
import org.aspectj.apache.bcel.generic.InstructionBranch;
import org.aspectj.apache.bcel.generic.InstructionHandle;
import org.aspectj.apache.bcel.generic.InstructionSelect;
import org.aspectj.apache.bcel.generic.MethodGen;
import org.aspectj.apache.bcel.generic.RET;
import org.aspectj.apache.bcel.verifier.InstructionWalker;
import org.aspectj.apache.bcel.verifier.exc.AssertionViolatedException;
import org.aspectj.apache.bcel.verifier.exc.StructuralCodeConstraintException;

/**
 * This class represents a control flow graph of a method.
 *
 * @version $Id: ControlFlowGraph.java,v 1.4 2009/09/09 19:56:20 aclement Exp $
 * @author <A HREF="https://www.inf.fu-berlin.de/~ehaase"/>Enver Haase</A>
 */
public class ControlFlowGraph {

	/**
	 * Objects of this class represent a node in a ControlFlowGraph. These nodes are instructions, not basic blocks.
	 */
	private class InstructionContextImpl implements InstructionContext {

		/**
		 * The TAG field is here for external temporary flagging, such as graph colouring.
		 *
		 * @see #getTag()
		 * @see #setTag(int)
		 */
		private int TAG;

		/**
		 * The InstructionHandle this InstructionContext is wrapped around.
		 */
		private final InstructionHandle instruction;

		/**
		 * The 'incoming' execution Frames.
		 */
		private final HashMap<InstructionContextImpl, Frame> inFrames; // key: the last-executed JSR

		/**
		 * The 'outgoing' execution Frames.
		 */
		private final HashMap<InstructionContextImpl, Frame> outFrames; // key: the last-executed JSR

		/**
		 * The 'execution predecessors' - a list of type InstructionContext of those instances that have been execute()d before in
		 * that order.
		 */
		private ArrayList<InstructionContext> executionPredecessors = null; // Type: InstructionContext

		/**
		 * Creates an InstructionHandleImpl object from an InstructionHandle. Creation of one per InstructionHandle suffices. Don't
		 * create more.
		 */
		public InstructionContextImpl(InstructionHandle inst) {
			if (inst == null) {
				throw new AssertionViolatedException("Cannot instantiate InstructionContextImpl from NULL.");
			}

			instruction = inst;
			inFrames = new java.util.HashMap<InstructionContextImpl, Frame>();
			outFrames = new java.util.HashMap<InstructionContextImpl, Frame>();
		}

		/* Satisfies InstructionContext.getTag(). */
		public int getTag() {
			return TAG;
		}

		/* Satisfies InstructionContext.setTag(int). */
		public void setTag(int tag) {
			TAG = tag;
		}

		/**
		 * Returns the exception handlers of this instruction.
		 */
		public ExceptionHandler[] getExceptionHandlers() {
			return exceptionhandlers.getExceptionHandlers(getInstruction());
		}

		/**
		 * Returns a clone of the "outgoing" frame situation with respect to the given ExecutionChain.
		 */
		public Frame getOutFrame(ArrayList<InstructionContext> execChain) {
			executionPredecessors = execChain;

			Frame org;

			InstructionContext jsr = lastExecutionJSR();

			org = outFrames.get(jsr);

			if (org == null) {
				throw new AssertionViolatedException("outFrame not set! This:\n" + this + "\nExecutionChain: "
						+ getExecutionChain() + "\nOutFrames: '" + outFrames + "'.");
			}
			return org.getClone();
		}

		/**
		 * "Merges in" (vmspec2, page 146) the "incoming" frame situation; executes the instructions symbolically and therefore
		 * calculates the "outgoing" frame situation. Returns: True iff the "incoming" frame situation changed after merging with
		 * "inFrame". The execPreds ArrayList must contain the InstructionContext objects executed so far in the correct order. This
		 * is just one execution path [out of many]. This is needed to correctly "merge" in the special case of a RET's successor.
		 * <B>The InstConstraintVisitor and ExecutionVisitor instances must be set up correctly.</B>
		 *
		 * @return true - if and only if the "outgoing" frame situation changed from the one before execute()ing.
		 */
		public boolean execute(Frame inFrame, ArrayList<InstructionContext> execPreds, InstConstraintVisitor icv, ExecutionVisitor ev) {

			executionPredecessors = (ArrayList<InstructionContext>) execPreds.clone();

			// sanity check
			if (lastExecutionJSR() == null && subroutines.subroutineOf(getInstruction()) != subroutines.getTopLevel()) {
				throw new AssertionViolatedException("Huh?! Am I '" + this + "' part of a subroutine or not?");
			}
			if (lastExecutionJSR() != null && subroutines.subroutineOf(getInstruction()) == subroutines.getTopLevel()) {
				throw new AssertionViolatedException("Huh?! Am I '" + this + "' part of a subroutine or not?");
			}

			Frame inF = inFrames.get(lastExecutionJSR());
			if (inF == null) {// no incoming frame was set, so set it.
				inFrames.put(lastExecutionJSR(), inFrame);
				inF = inFrame;
			} else {// if there was an "old" inFrame
				if (inF.equals(inFrame)) { // shortcut: no need to merge equal frames.
					return false;
				}
				if (!mergeInFrames(inFrame)) {
					return false;
				}
			}

			// Now we're sure the inFrame has changed!

			// new inFrame is already merged in, see above.
			Frame workingFrame = inF.getClone();

			try {
				// This verifies the InstructionConstraint for the current
				// instruction, but does not modify the workingFrame object.
				// InstConstraintVisitor icv =
				// InstConstraintVisitor.getInstance(VerifierFactory.getVerifier(method_gen.getClassName()));
				icv.setFrame(workingFrame);
				InstructionWalker.accept(getInstruction().getInstruction(), icv);
			} catch (StructuralCodeConstraintException ce) {
				ce.extendMessage("", "\nInstructionHandle: " + getInstruction() + "\n");
				ce.extendMessage("", "\nExecution Frame:\n" + workingFrame);
				extendMessageWithFlow(ce);
				throw ce;
			}

			// This executes the Instruction.
			// Therefore the workingFrame object is modified.
			// ExecutionVisitor ev = ExecutionVisitor.getInstance(VerifierFactory.getVerifier(method_gen.getClassName()));
			ev.setFrame(workingFrame);
			InstructionWalker.accept(getInstruction().getInstruction(), ev);
			// getInstruction().accept(ExecutionVisitor.withFrame(workingFrame));
			outFrames.put(lastExecutionJSR(), workingFrame);

			return true; // new inFrame was different from old inFrame so merging them
			// yielded a different this.inFrame.
		}

		/**
		 * Returns a simple String representation of this InstructionContext.
		 */
		public String toString() {
			// TODO: Put information in the brackets, e.g.
			// Is this an ExceptionHandler? Is this a RET? Is this the start of
			// a subroutine?
			String ret = getInstruction().toString(false) + "\t[InstructionContext]";
			return ret;
		}

		/**
		 * Does the actual merging (vmspec2, page 146). Returns true IFF this.inFrame was changed in course of merging with inFrame.
		 */
		private boolean mergeInFrames(Frame inFrame) {
			// TODO: Can be performance-improved.
			Frame inF = inFrames.get(lastExecutionJSR());
			OperandStack oldstack = inF.getStack().getClone();
			LocalVariables oldlocals = inF.getLocals().getClone();
			try {
				inF.getStack().merge(inFrame.getStack());
				inF.getLocals().merge(inFrame.getLocals());
			} catch (StructuralCodeConstraintException sce) {
				extendMessageWithFlow(sce);
				throw sce;
			}
			if (oldstack.equals(inF.getStack()) && oldlocals.equals(inF.getLocals())) {
				return false;
			} else {
				return true;
			}
		}

		/**
		 * Returns the control flow execution chain. This is built while execute(Frame, ArrayList)-ing the code represented by the
		 * surrounding ControlFlowGraph.
		 */
		private String getExecutionChain() {
			String s = this.toString();
			for (int i = executionPredecessors.size() - 1; i >= 0; i--) {
				s = executionPredecessors.get(i) + "\n" + s;
			}
			return s;
		}

		/**
		 * Extends the StructuralCodeConstraintException ("e") object with an at-the-end-extended message. This extended message
		 * will then reflect the execution flow needed to get to the constraint violation that triggered the throwing of the "e"
		 * object.
		 */
		private void extendMessageWithFlow(StructuralCodeConstraintException e) {
			String s = "Execution flow:\n";
			e.extendMessage("", s + getExecutionChain());
		}

		/*
		 * Fulfils the contract of InstructionContext.getInstruction().
		 */
		public InstructionHandle getInstruction() {
			return instruction;
		}

		/**
		 * Returns the InstructionContextImpl with an JSR/JSR_W that was last in the ExecutionChain, without a corresponding RET,
		 * i.e. we were called by this one. Returns null if we were called from the top level.
		 */
		private InstructionContextImpl lastExecutionJSR() {

			int size = executionPredecessors.size();
			int retcount = 0;

			for (int i = size - 1; i >= 0; i--) {
				InstructionContextImpl current = (InstructionContextImpl) executionPredecessors.get(i);
				Instruction currentlast = current.getInstruction().getInstruction();
				if (currentlast instanceof RET) {
					retcount++;
				}
				if (currentlast.isJsrInstruction()) {
					retcount--;
					if (retcount == -1) {
						return current;
					}
				}
			}
			return null;
		}

		/* Satisfies InstructionContext.getSuccessors(). */
		public InstructionContext[] getSuccessors() {
			return contextsOf(_getSuccessors());
		}

		/**
		 * A utility method that calculates the successors of a given InstructionHandle That means, a RET does have successors as
		 * defined here. A JsrInstruction has its target as its successor (opposed to its physical successor) as defined here.
		 */
		// TODO: implement caching!
		private InstructionHandle[] _getSuccessors() {
			final InstructionHandle[] empty = new InstructionHandle[0];
			final InstructionHandle[] single = new InstructionHandle[1];
			final InstructionHandle[] pair = new InstructionHandle[2];

			Instruction inst = getInstruction().getInstruction();

			if (inst instanceof RET) {
				Subroutine s = subroutines.subroutineOf(getInstruction());
				if (s == null) { // return empty; // RET in dead code. "empty" would be the correct answer, but we know something
					// about the surrounding project...
					throw new AssertionViolatedException("Asking for successors of a RET in dead code?!");
				}
				// TODO: remove
				throw new AssertionViolatedException("DID YOU REALLY WANT TO ASK FOR RET'S SUCCS?");
				/*
				 * InstructionHandle[] jsrs = s.getEnteringJsrInstructions(); InstructionHandle[] ret = new
				 * InstructionHandle[jsrs.length]; for (int i=0; i<jsrs.length; i++){ ret[i] = jsrs[i].getNext(); } return ret;
				 */
			}

			// Terminates method normally.
			if (inst.isReturnInstruction()) {
				return empty;
			}

			// Terminates method abnormally, because JustIce mandates
			// subroutines not to be protected by exception handlers.
			if (inst.getOpcode() == Constants.ATHROW) {
				return empty;
			}

			// See method comment.
			if (inst.isJsrInstruction()) {
				single[0] = ((InstructionBranch) inst).getTarget();
				return single;
			}

			if (inst.getOpcode() == Constants.GOTO || inst.getOpcode() == Constants.GOTO_W) {
				single[0] = ((InstructionBranch) inst).getTarget();
				return single;
			}

			if (inst instanceof InstructionBranch) {
				if (inst instanceof InstructionSelect) {
					// BCEL's getTargets() returns only the non-default targets,
					// thanks to Eli Tilevich for reporting.
					InstructionHandle[] matchTargets = ((InstructionSelect) inst).getTargets();
					InstructionHandle[] ret = new InstructionHandle[matchTargets.length + 1];
					ret[0] = ((InstructionSelect) inst).getTarget();
					System.arraycopy(matchTargets, 0, ret, 1, matchTargets.length);
					return ret;
				} else {
					pair[0] = getInstruction().getNext();
					pair[1] = ((InstructionBranch) inst).getTarget();
					return pair;
				}
			}

			// default case: Fall through.
			single[0] = getInstruction().getNext();
			return single;
		}

	} // End Inner InstructionContextImpl Class.

	/** The MethofGen object we're working on. */
	private final MethodGen method_gen;

	/** The Subroutines object for the method whose control flow is represented by this ControlFlowGraph. */
	private final Subroutines subroutines;

	/** The ExceptionHandlers object for the method whose control flow is represented by this ControlFlowGraph. */
	private final ExceptionHandlers exceptionhandlers;

	/** All InstructionContext instances of this ControlFlowGraph. */
	private final Hashtable<InstructionHandle, InstructionContextImpl> instructionContexts = new Hashtable<InstructionHandle, InstructionContextImpl>(); // keys: InstructionHandle, values: InstructionContextImpl

	/**
	 * A Control Flow Graph.
	 */
	public ControlFlowGraph(MethodGen method_gen) {
		subroutines = new Subroutines(method_gen);
		exceptionhandlers = new ExceptionHandlers(method_gen);

		InstructionHandle[] instructionhandles = method_gen.getInstructionList().getInstructionHandles();
		for (int i = 0; i < instructionhandles.length; i++) {
			instructionContexts.put(instructionhandles[i], new InstructionContextImpl(instructionhandles[i]));
		}

		this.method_gen = method_gen;
	}

	/**
	 * Returns the InstructionContext of a given instruction.
	 */
	public InstructionContext contextOf(InstructionHandle inst) {
		InstructionContext ic = instructionContexts.get(inst);
		if (ic == null) {
			throw new AssertionViolatedException("InstructionContext requested for an InstructionHandle that's not known!");
		}
		return ic;
	}

	/**
	 * Returns the InstructionContext[] of a given InstructionHandle[], in a naturally ordered manner.
	 */
	public InstructionContext[] contextsOf(InstructionHandle[] insts) {
		InstructionContext[] ret = new InstructionContext[insts.length];
		for (int i = 0; i < insts.length; i++) {
			ret[i] = contextOf(insts[i]);
		}
		return ret;
	}

	/**
	 * Returns an InstructionContext[] with all the InstructionContext instances for the method whose control flow is represented by
	 * this ControlFlowGraph <B>(NOT ORDERED!)</B>.
	 */
	public InstructionContext[] getInstructionContexts() {
		InstructionContext[] ret = new InstructionContext[instructionContexts.values().size()];
		return instructionContexts.values().toArray(ret);
	}

	/**
	 * Returns true, if and only if the said instruction is not reachable; that means, if it not part of this ControlFlowGraph.
	 */
	public boolean isDead(InstructionHandle i) {
		return instructionContexts.containsKey(i);
	}
}