001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 *  Unless required by applicable law or agreed to in writing, software
012 *  distributed under the License is distributed on an "AS IS" BASIS,
013 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 *  See the License for the specific language governing permissions and
015 *  limitations under the License.
016 */
017package org.apache.bcel.generic;
018
019import java.io.ByteArrayOutputStream;
020import java.io.DataOutputStream;
021import java.io.IOException;
022import java.util.ArrayList;
023import java.util.Arrays;
024import java.util.HashMap;
025import java.util.Iterator;
026import java.util.List;
027import java.util.Map;
028import java.util.NoSuchElementException;
029
030import org.apache.bcel.Const;
031import org.apache.bcel.classfile.Constant;
032import org.apache.bcel.util.ByteSequence;
033import org.apache.commons.lang3.ArrayUtils;
034import org.apache.commons.lang3.stream.Streams;
035
036/**
037 * This class is a container for a list of <a href="Instruction.html">Instruction</a> objects. Instructions can be
038 * appended, inserted, moved, deleted, etc.. Instructions are being wrapped into
039 * <a href="InstructionHandle.html">InstructionHandles</a> objects that are returned upon append/insert operations. They
040 * give the user (read only) access to the list structure, such that it can be traversed and manipulated in a controlled
041 * way.
042 *
043 * A list is finally dumped to a byte code array with <a href="#getByteCode()">getByteCode</a>.
044 *
045 * @see Instruction
046 * @see InstructionHandle
047 * @see BranchHandle
048 */
049public class InstructionList implements Iterable<InstructionHandle> {
050
051    /**
052     * Find the target instruction (handle) that corresponds to the given target position (byte code offset).
053     *
054     * @param ihs array of instruction handles, i.e. il.getInstructionHandles()
055     * @param pos array of positions corresponding to ihs, i.e. il.getInstructionPositions()
056     * @param count length of arrays
057     * @param target target position to search for
058     * @return target position's instruction handle if available
059     */
060    public static InstructionHandle findHandle(final InstructionHandle[] ihs, final int[] pos, final int count, final int target) {
061        if (ihs != null && pos != null) {
062            int l = 0;
063            int r = count - 1;
064            /*
065             * Do a binary search since the pos array is orderd.
066             */
067            do {
068                final int i = l + r >>> 1;
069                final int j = pos[i];
070                if (j == target) {
071                    return ihs[i];
072                }
073                if (target < j) {
074                    r = i - 1;
075                } else {
076                    l = i + 1;
077                }
078            } while (l <= r);
079        }
080        return null;
081    }
082
083    private InstructionHandle start;
084    private InstructionHandle end;
085    private int length; // number of elements in list
086
087    private int[] bytePositions; // byte code offsets corresponding to instructions
088
089    private List<InstructionListObserver> observers;
090
091    /**
092     * Create (empty) instruction list.
093     */
094    public InstructionList() {
095    }
096
097    /**
098     * Create instruction list containing one instruction.
099     *
100     * @param i initial instruction
101     */
102    public InstructionList(final BranchInstruction i) {
103        append(i);
104    }
105
106    /**
107     * Initialize instruction list from byte array.
108     *
109     * @param code byte array containing the instructions
110     */
111    public InstructionList(final byte[] code) {
112        int count = 0; // Contains actual length
113        int[] pos;
114        InstructionHandle[] ihs;
115        try (ByteSequence bytes = new ByteSequence(code)) {
116            ihs = new InstructionHandle[code.length];
117            pos = new int[code.length]; // Can't be more than that
118            /*
119             * Pass 1: Create an object for each byte code and append them to the list.
120             */
121            while (bytes.available() > 0) {
122                // Remember byte offset and associate it with the instruction
123                final int off = bytes.getIndex();
124                pos[count] = off;
125                /*
126                 * Read one instruction from the byte stream, the byte position is set accordingly.
127                 */
128                final Instruction i = Instruction.readInstruction(bytes);
129                InstructionHandle ih;
130                if (i instanceof BranchInstruction) {
131                    ih = append((BranchInstruction) i);
132                } else {
133                    ih = append(i);
134                }
135                ih.setPosition(off);
136                ihs[count] = ih;
137                count++;
138            }
139        } catch (final IOException e) {
140            throw new ClassGenException(e.toString(), e);
141        }
142        bytePositions = Arrays.copyOf(pos, count); // Trim to proper size
143        /*
144         * Pass 2: Look for BranchInstruction and update their targets, i.e., convert offsets to instruction handles.
145         */
146        for (int i = 0; i < count; i++) {
147            if (ihs[i] instanceof BranchHandle) {
148                final BranchInstruction bi = (BranchInstruction) ihs[i].getInstruction();
149                int target = bi.getPosition() + bi.getIndex(); /*
150                                                                * Byte code position: relative -> absolute.
151                                                                */
152                // Search for target position
153                InstructionHandle ih = findHandle(ihs, pos, count, target);
154                if (ih == null) {
155                    throw new ClassGenException("Couldn't find target for branch: " + bi);
156                }
157                bi.setTarget(ih); // Update target
158                // If it is a Select instruction, update all branch targets
159                if (bi instanceof Select) { // Either LOOKUPSWITCH or TABLESWITCH
160                    final Select s = (Select) bi;
161                    final int[] indices = s.getIndices();
162                    for (int j = 0; j < indices.length; j++) {
163                        target = bi.getPosition() + indices[j];
164                        ih = findHandle(ihs, pos, count, target);
165                        if (ih == null) {
166                            throw new ClassGenException("Couldn't find target for switch: " + bi);
167                        }
168                        s.setTarget(j, ih); // Update target
169                    }
170                }
171            }
172        }
173    }
174
175    /**
176     * Initialize list with (nonnull) compound instruction. Consumes argument list, i.e., it becomes empty.
177     *
178     * @param c compound instruction (list)
179     */
180    public InstructionList(final CompoundInstruction c) {
181        append(c.getInstructionList());
182    }
183
184    /**
185     * Create instruction list containing one instruction.
186     *
187     * @param i initial instruction
188     */
189    public InstructionList(final Instruction i) {
190        append(i);
191    }
192
193    /**
194     * Add observer for this object.
195     */
196    public void addObserver(final InstructionListObserver o) {
197        if (observers == null) {
198            observers = new ArrayList<>();
199        }
200        observers.add(o);
201    }
202
203    /**
204     * Append a branch instruction to the end of this list.
205     *
206     * @param i branch instruction to append
207     * @return branch instruction handle of the appended instruction
208     */
209    public BranchHandle append(final BranchInstruction i) {
210        final BranchHandle ih = BranchHandle.getBranchHandle(i);
211        append(ih);
212        return ih;
213    }
214
215    /**
216     * Append a compound instruction.
217     *
218     * @param c The composite instruction (containing an InstructionList)
219     * @return instruction handle of the first appended instruction
220     */
221    public InstructionHandle append(final CompoundInstruction c) {
222        return append(c.getInstructionList());
223    }
224
225    /**
226     * Append an instruction to the end of this list.
227     *
228     * @param i instruction to append
229     * @return instruction handle of the appended instruction
230     */
231    public InstructionHandle append(final Instruction i) {
232        final InstructionHandle ih = InstructionHandle.getInstructionHandle(i);
233        append(ih);
234        return ih;
235    }
236
237    /**
238     * Append a compound instruction, after instruction i.
239     *
240     * @param i Instruction in list
241     * @param c The composite instruction (containing an InstructionList)
242     * @return instruction handle of the first appended instruction
243     */
244    public InstructionHandle append(final Instruction i, final CompoundInstruction c) {
245        return append(i, c.getInstructionList());
246    }
247
248    /**
249     * Append a single instruction j after another instruction i, which must be in this list of course!
250     *
251     * @param i Instruction in list
252     * @param j Instruction to append after i in list
253     * @return instruction handle of the first appended instruction
254     */
255    public InstructionHandle append(final Instruction i, final Instruction j) {
256        return append(i, new InstructionList(j));
257    }
258
259    /**
260     * Append another list after instruction i contained in this list. Consumes argument list, i.e., it becomes empty.
261     *
262     * @param i where to append the instruction list
263     * @param il Instruction list to append to this one
264     * @return instruction handle pointing to the <B>first</B> appended instruction
265     */
266    public InstructionHandle append(final Instruction i, final InstructionList il) {
267        InstructionHandle ih;
268        if ((ih = findInstruction2(i)) == null) {
269            throw new ClassGenException("Instruction " + i + " is not contained in this list.");
270        }
271        return append(ih, il);
272    }
273
274    /**
275     * Append an instruction to the end of this list.
276     *
277     * @param ih instruction to append
278     */
279    private void append(final InstructionHandle ih) {
280        if (isEmpty()) {
281            start = end = ih;
282            ih.setNext(ih.setPrev(null));
283        } else {
284            end.setNext(ih);
285            ih.setPrev(end);
286            ih.setNext(null);
287            end = ih;
288        }
289        length++; // Update length
290    }
291
292    /**
293     * Append an instruction after instruction (handle) ih contained in this list.
294     *
295     * @param ih where to append the instruction list
296     * @param i Instruction to append
297     * @return instruction handle pointing to the <B>first</B> appended instruction
298     */
299    public BranchHandle append(final InstructionHandle ih, final BranchInstruction i) {
300        final BranchHandle bh = BranchHandle.getBranchHandle(i);
301        final InstructionList il = new InstructionList();
302        il.append(bh);
303        append(ih, il);
304        return bh;
305    }
306
307    /**
308     * Append a compound instruction.
309     *
310     * @param ih where to append the instruction list
311     * @param c The composite instruction (containing an InstructionList)
312     * @return instruction handle of the first appended instruction
313     */
314    public InstructionHandle append(final InstructionHandle ih, final CompoundInstruction c) {
315        return append(ih, c.getInstructionList());
316    }
317
318    /**
319     * Append an instruction after instruction (handle) ih contained in this list.
320     *
321     * @param ih where to append the instruction list
322     * @param i Instruction to append
323     * @return instruction handle pointing to the <B>first</B> appended instruction
324     */
325    public InstructionHandle append(final InstructionHandle ih, final Instruction i) {
326        return append(ih, new InstructionList(i));
327    }
328
329    /**
330     * Append another list after instruction (handle) ih contained in this list. Consumes argument list, i.e., it becomes
331     * empty.
332     *
333     * @param ih where to append the instruction list
334     * @param il Instruction list to append to this one
335     * @return instruction handle pointing to the <B>first</B> appended instruction
336     */
337    public InstructionHandle append(final InstructionHandle ih, final InstructionList il) {
338        if (il == null) {
339            throw new ClassGenException("Appending null InstructionList");
340        }
341        if (il.isEmpty()) {
342            return ih;
343        }
344        final InstructionHandle next = ih.getNext();
345        final InstructionHandle ret = il.start;
346        ih.setNext(il.start);
347        il.start.setPrev(ih);
348        il.end.setNext(next);
349        if (next != null) {
350            next.setPrev(il.end);
351        } else {
352            end = il.end; // Update end ...
353        }
354        length += il.length; // Update length
355        il.clear();
356        return ret;
357    }
358
359    /**
360     * Append another list to this one. Consumes argument list, i.e., it becomes empty.
361     *
362     * @param il list to append to end of this list
363     * @return instruction handle of the <B>first</B> appended instruction
364     */
365    public InstructionHandle append(final InstructionList il) {
366        if (il == null) {
367            throw new ClassGenException("Appending null InstructionList");
368        }
369        if (il.isEmpty()) {
370            return null;
371        }
372        if (isEmpty()) {
373            start = il.start;
374            end = il.end;
375            length = il.length;
376            il.clear();
377            return start;
378        }
379        return append(end, il); // was end.instruction
380    }
381
382    private void clear() {
383        start = end = null;
384        length = 0;
385    }
386
387    public boolean contains(final Instruction i) {
388        return findInstruction1(i) != null;
389    }
390
391    public boolean contains(final InstructionHandle i) {
392        if (i == null) {
393            return false;
394        }
395        for (InstructionHandle ih = start; ih != null; ih = ih.getNext()) {
396            if (ih == i) {
397                return true;
398            }
399        }
400        return false;
401    }
402
403    /**
404     * @return complete, i.e., deep copy of this list
405     */
406    public InstructionList copy() {
407        final Map<InstructionHandle, InstructionHandle> map = new HashMap<>();
408        final InstructionList il = new InstructionList();
409        /*
410         * Pass 1: Make copies of all instructions, append them to the new list and associate old instruction references with
411         * the new ones, i.e., a 1:1 mapping.
412         */
413        for (InstructionHandle ih = start; ih != null; ih = ih.getNext()) {
414            final Instruction i = ih.getInstruction();
415            final Instruction c = i.copy(); // Use clone for shallow copy
416            if (c instanceof BranchInstruction) {
417                map.put(ih, il.append((BranchInstruction) c));
418            } else {
419                map.put(ih, il.append(c));
420            }
421        }
422        /*
423         * Pass 2: Update branch targets.
424         */
425        InstructionHandle ih = start;
426        InstructionHandle ch = il.start;
427        while (ih != null) {
428            final Instruction i = ih.getInstruction();
429            final Instruction c = ch.getInstruction();
430            if (i instanceof BranchInstruction) {
431                final BranchInstruction bi = (BranchInstruction) i;
432                final BranchInstruction bc = (BranchInstruction) c;
433                final InstructionHandle itarget = bi.getTarget(); // old target
434                // New target is in hash map
435                bc.setTarget(map.get(itarget));
436                if (bi instanceof Select) { // Either LOOKUPSWITCH or TABLESWITCH
437                    final InstructionHandle[] itargets = ((Select) bi).getTargets();
438                    final InstructionHandle[] ctargets = ((Select) bc).getTargets();
439                    for (int j = 0; j < itargets.length; j++) { // Update all targets
440                        ctargets[j] = map.get(itargets[j]);
441                    }
442                }
443            }
444            ih = ih.getNext();
445            ch = ch.getNext();
446        }
447        return il;
448    }
449
450    /**
451     * Remove instruction from this list. The corresponding Instruction handles must not be reused!
452     *
453     * @param i instruction to remove
454     */
455    public void delete(final Instruction i) throws TargetLostException {
456        InstructionHandle ih;
457        if ((ih = findInstruction1(i)) == null) {
458            throw new ClassGenException("Instruction " + i + " is not contained in this list.");
459        }
460        delete(ih);
461    }
462
463    /**
464     * Remove instructions from instruction 'from' to instruction 'to' contained in this list. The user must ensure that
465     * 'from' is an instruction before 'to', or risk havoc. The corresponding Instruction handles must not be reused!
466     *
467     * @param from where to start deleting (inclusive)
468     * @param to where to end deleting (inclusive)
469     */
470    public void delete(final Instruction from, final Instruction to) throws TargetLostException {
471        InstructionHandle fromIh;
472        InstructionHandle toIh;
473        if ((fromIh = findInstruction1(from)) == null) {
474            throw new ClassGenException("Instruction " + from + " is not contained in this list.");
475        }
476        if ((toIh = findInstruction2(to)) == null) {
477            throw new ClassGenException("Instruction " + to + " is not contained in this list.");
478        }
479        delete(fromIh, toIh);
480    }
481
482    /**
483     * Remove instruction from this list. The corresponding Instruction handles must not be reused!
484     *
485     * @param ih instruction (handle) to remove
486     */
487    public void delete(final InstructionHandle ih) throws TargetLostException {
488        remove(ih.getPrev(), ih.getNext());
489    }
490
491    /**
492     * Remove instructions from instruction 'from' to instruction 'to' contained in this list. The user must ensure that
493     * 'from' is an instruction before 'to', or risk havoc. The corresponding Instruction handles must not be reused!
494     *
495     * @param from where to start deleting (inclusive)
496     * @param to where to end deleting (inclusive)
497     */
498    public void delete(final InstructionHandle from, final InstructionHandle to) throws TargetLostException {
499        remove(from.getPrev(), to.getNext());
500    }
501
502    /**
503     * Delete contents of list. Provides better memory utilization, because the system then may reuse the instruction
504     * handles. This method is typically called right after {@link MethodGen#getMethod()}.
505     */
506    public void dispose() {
507        // Traverse in reverse order, because ih.next is overwritten
508        for (InstructionHandle ih = end; ih != null; ih = ih.getPrev()) {
509            // Causes BranchInstructions to release target and targeters, because it calls dispose() on the contained instruction.
510            ih.dispose();
511        }
512        clear();
513    }
514
515    /**
516     * Gets instruction handle for instruction at byte code position pos. This only works properly, if the list is freshly
517     * initialized from a byte array or setPositions() has been called before this method.
518     *
519     * @param pos byte code position to search for
520     * @return target position's instruction handle if available
521     */
522    public InstructionHandle findHandle(final int pos) {
523        final int[] positions = bytePositions;
524        InstructionHandle ih = start;
525        for (int i = 0; i < length; i++) {
526            if (positions[i] == pos) {
527                return ih;
528            }
529            ih = ih.getNext();
530        }
531        return null;
532    }
533
534    /**
535     * Search for given Instruction reference, start at beginning of list.
536     *
537     * @param i instruction to search for
538     * @return instruction found on success, null otherwise
539     */
540    private InstructionHandle findInstruction1(final Instruction i) {
541        for (InstructionHandle ih = start; ih != null; ih = ih.getNext()) {
542            if (ih.getInstruction() == i) {
543                return ih;
544            }
545        }
546        return null;
547    }
548
549    /**
550     * Search for given Instruction reference, start at end of list
551     *
552     * @param i instruction to search for
553     * @return instruction found on success, null otherwise
554     */
555    private InstructionHandle findInstruction2(final Instruction i) {
556        for (InstructionHandle ih = end; ih != null; ih = ih.getPrev()) {
557            if (ih.getInstruction() == i) {
558                return ih;
559            }
560        }
561        return null;
562    }
563
564    /**
565     * When everything is finished, use this method to convert the instruction list into an array of bytes.
566     *
567     * @return the byte code ready to be dumped
568     */
569    public byte[] getByteCode() {
570        // Update position indices of instructions
571        setPositions();
572        final ByteArrayOutputStream b = new ByteArrayOutputStream();
573        final DataOutputStream out = new DataOutputStream(b);
574        try {
575            for (InstructionHandle ih = start; ih != null; ih = ih.getNext()) {
576                final Instruction i = ih.getInstruction();
577                i.dump(out); // Traverse list
578            }
579            out.flush();
580        } catch (final IOException e) {
581            System.err.println(e);
582            return ArrayUtils.EMPTY_BYTE_ARRAY;
583        }
584        return b.toByteArray();
585    }
586
587    /**
588     * @return end of list
589     */
590    public InstructionHandle getEnd() {
591        return end;
592    }
593
594    /**
595     * @return array containing all instructions (handles)
596     */
597    public InstructionHandle[] getInstructionHandles() {
598        final InstructionHandle[] ihs = new InstructionHandle[length];
599        InstructionHandle ih = start;
600        for (int i = 0; i < length; i++) {
601            ihs[i] = ih;
602            ih = ih.getNext();
603        }
604        return ihs;
605    }
606
607    /**
608     * Gets positions (offsets) of all instructions in the list. This relies on that the list has been freshly created from
609     * an byte code array, or that setPositions() has been called. Otherwise this may be inaccurate.
610     *
611     * @return array containing all instruction's offset in byte code
612     */
613    public int[] getInstructionPositions() {
614        return bytePositions;
615    }
616
617    /**
618     * @return an array of instructions without target information for branch instructions.
619     */
620    public Instruction[] getInstructions() {
621        final List<Instruction> instructions = new ArrayList<>();
622        try (ByteSequence bytes = new ByteSequence(getByteCode())) {
623            while (bytes.available() > 0) {
624                instructions.add(Instruction.readInstruction(bytes));
625            }
626        } catch (final IOException e) {
627            throw new ClassGenException(e.toString(), e);
628        }
629        return instructions.toArray(Instruction.EMPTY_ARRAY);
630    }
631
632    /**
633     * @return length of list (Number of instructions, not bytes)
634     */
635    public int getLength() {
636        return length;
637    }
638
639    /**
640     * @return start of list
641     */
642    public InstructionHandle getStart() {
643        return start;
644    }
645
646    /**
647     * Insert a branch instruction at start of this list.
648     *
649     * @param i branch instruction to insert
650     * @return branch instruction handle of the appended instruction
651     */
652    public BranchHandle insert(final BranchInstruction i) {
653        final BranchHandle ih = BranchHandle.getBranchHandle(i);
654        insert(ih);
655        return ih;
656    }
657
658    /**
659     * Insert a compound instruction.
660     *
661     * @param c The composite instruction (containing an InstructionList)
662     * @return instruction handle of the first inserted instruction
663     */
664    public InstructionHandle insert(final CompoundInstruction c) {
665        return insert(c.getInstructionList());
666    }
667
668    /**
669     * Insert an instruction at start of this list.
670     *
671     * @param i instruction to insert
672     * @return instruction handle of the inserted instruction
673     */
674    public InstructionHandle insert(final Instruction i) {
675        final InstructionHandle ih = InstructionHandle.getInstructionHandle(i);
676        insert(ih);
677        return ih;
678    }
679
680    /**
681     * Insert a compound instruction before instruction i.
682     *
683     * @param i Instruction in list
684     * @param c The composite instruction (containing an InstructionList)
685     * @return instruction handle of the first inserted instruction
686     */
687    public InstructionHandle insert(final Instruction i, final CompoundInstruction c) {
688        return insert(i, c.getInstructionList());
689    }
690
691    /**
692     * Insert a single instruction j before another instruction i, which must be in this list of course!
693     *
694     * @param i Instruction in list
695     * @param j Instruction to insert before i in list
696     * @return instruction handle of the first inserted instruction
697     */
698    public InstructionHandle insert(final Instruction i, final Instruction j) {
699        return insert(i, new InstructionList(j));
700    }
701
702    /**
703     * Insert another list before Instruction i contained in this list. Consumes argument list, i.e., it becomes empty.
704     *
705     * @param i where to append the instruction list
706     * @param il Instruction list to insert
707     * @return instruction handle pointing to the first inserted instruction, i.e., il.getStart()
708     */
709    public InstructionHandle insert(final Instruction i, final InstructionList il) {
710        InstructionHandle ih;
711        if ((ih = findInstruction1(i)) == null) {
712            throw new ClassGenException("Instruction " + i + " is not contained in this list.");
713        }
714        return insert(ih, il);
715    }
716
717    /**
718     * Insert an instruction at start of this list.
719     *
720     * @param ih instruction to insert
721     */
722    private void insert(final InstructionHandle ih) {
723        if (isEmpty()) {
724            start = end = ih;
725            ih.setNext(ih.setPrev(null));
726        } else {
727            start.setPrev(ih);
728            ih.setNext(start);
729            ih.setPrev(null);
730            start = ih;
731        }
732        length++;
733    }
734
735    /**
736     * Insert an instruction before instruction (handle) ih contained in this list.
737     *
738     * @param ih where to insert to the instruction list
739     * @param i Instruction to insert
740     * @return instruction handle of the first inserted instruction
741     */
742    public BranchHandle insert(final InstructionHandle ih, final BranchInstruction i) {
743        final BranchHandle bh = BranchHandle.getBranchHandle(i);
744        final InstructionList il = new InstructionList();
745        il.append(bh);
746        insert(ih, il);
747        return bh;
748    }
749
750    /**
751     * Insert a compound instruction.
752     *
753     * @param ih where to insert the instruction list
754     * @param c The composite instruction (containing an InstructionList)
755     * @return instruction handle of the first inserted instruction
756     */
757    public InstructionHandle insert(final InstructionHandle ih, final CompoundInstruction c) {
758        return insert(ih, c.getInstructionList());
759    }
760
761    /**
762     * Insert an instruction before instruction (handle) ih contained in this list.
763     *
764     * @param ih where to insert to the instruction list
765     * @param i Instruction to insert
766     * @return instruction handle of the first inserted instruction
767     */
768    public InstructionHandle insert(final InstructionHandle ih, final Instruction i) {
769        return insert(ih, new InstructionList(i));
770    }
771
772    /**
773     * Insert another list before Instruction handle ih contained in this list. Consumes argument list, i.e., it becomes
774     * empty.
775     *
776     * @param ih where to append the instruction list
777     * @param il Instruction list to insert
778     * @return instruction handle of the first inserted instruction
779     */
780    public InstructionHandle insert(final InstructionHandle ih, final InstructionList il) {
781        if (il == null) {
782            throw new ClassGenException("Inserting null InstructionList");
783        }
784        if (il.isEmpty()) {
785            return ih;
786        }
787        final InstructionHandle prev = ih.getPrev();
788        final InstructionHandle ret = il.start;
789        ih.setPrev(il.end);
790        il.end.setNext(ih);
791        il.start.setPrev(prev);
792        if (prev != null) {
793            prev.setNext(il.start);
794        } else {
795            start = il.start; // Update start ...
796        }
797        length += il.length; // Update length
798        il.clear();
799        return ret;
800    }
801
802    /**
803     * Insert another list.
804     *
805     * @param il list to insert before start of this list
806     * @return instruction handle of the first inserted instruction
807     */
808    public InstructionHandle insert(final InstructionList il) {
809        if (isEmpty()) {
810            append(il); // Code is identical for this case
811            return start;
812        }
813        return insert(start, il);
814    }
815
816    /**
817     * Test for empty list.
818     */
819    public boolean isEmpty() {
820        return start == null;
821    } // && end == null
822
823    /**
824     * @return iterator that lists all instructions (handles)
825     */
826    @Override
827    public Iterator<InstructionHandle> iterator() {
828        return new Iterator<InstructionHandle>() {
829
830            private InstructionHandle ih = start;
831
832            @Override
833            public boolean hasNext() {
834                return ih != null;
835            }
836
837            @Override
838            public InstructionHandle next() throws NoSuchElementException {
839                if (ih == null) {
840                    throw new NoSuchElementException();
841                }
842                final InstructionHandle i = ih;
843                ih = ih.getNext();
844                return i;
845            }
846
847            @Override
848            public void remove() {
849                throw new UnsupportedOperationException();
850            }
851        };
852    }
853
854    /**
855     * Move a single instruction (handle) to a new location.
856     *
857     * @param ih moved instruction
858     * @param target new location of moved instruction
859     */
860    public void move(final InstructionHandle ih, final InstructionHandle target) {
861        move(ih, ih, target);
862    }
863
864    /**
865     * Take all instructions (handles) from "start" to "end" and append them after the new location "target". Of course,
866     * "end" must be after "start" and target must not be located withing this range. If you want to move something to the
867     * start of the list use null as value for target.
868     * <p>
869     * Any instruction targeters pointing to handles within the block, keep their targets.
870     * </p>
871     *
872     * @param start of moved block
873     * @param end of moved block
874     * @param target of moved block
875     */
876    public void move(final InstructionHandle start, final InstructionHandle end, final InstructionHandle target) {
877        // Step 1: Check constraints
878        if (start == null || end == null) {
879            throw new ClassGenException("Invalid null handle: From " + start + " to " + end);
880        }
881        if (target == start || target == end) {
882            throw new ClassGenException("Invalid range: From " + start + " to " + end + " contains target " + target);
883        }
884        for (InstructionHandle ih = start; ih != end.getNext(); ih = ih.getNext()) {
885            if (ih == null) {
886                throw new ClassGenException("Invalid range: From " + start + " to " + end);
887            }
888            if (ih == target) {
889                throw new ClassGenException("Invalid range: From " + start + " to " + end + " contains target " + target);
890            }
891        }
892        // Step 2: Temporarily remove the given instructions from the list
893        final InstructionHandle prev = start.getPrev();
894        InstructionHandle next = end.getNext();
895        if (prev != null) {
896            prev.setNext(next);
897        } else {
898            this.start = next;
899        }
900        if (next != null) {
901            next.setPrev(prev);
902        } else {
903            this.end = prev;
904        }
905        start.setPrev(end.setNext(null));
906        // Step 3: append after target
907        if (target == null) { // append to start of list
908            if (this.start != null) {
909                this.start.setPrev(end);
910            }
911            end.setNext(this.start);
912            this.start = start;
913        } else {
914            next = target.getNext();
915            target.setNext(start);
916            start.setPrev(target);
917            end.setNext(next);
918            if (next != null) {
919                next.setPrev(end);
920            } else {
921                this.end = end;
922            }
923        }
924    }
925
926    /**
927     * Redirect all references from oldTarget to newTarget, i.e., update targets of branch instructions.
928     *
929     * @param oldTarget the old target instruction handle
930     * @param newTarget the new target instruction handle
931     */
932    public void redirectBranches(final InstructionHandle oldTarget, final InstructionHandle newTarget) {
933        for (InstructionHandle ih = start; ih != null; ih = ih.getNext()) {
934            final Instruction i = ih.getInstruction();
935            if (i instanceof BranchInstruction) {
936                final BranchInstruction b = (BranchInstruction) i;
937                final InstructionHandle target = b.getTarget();
938                if (target == oldTarget) {
939                    b.setTarget(newTarget);
940                }
941                if (b instanceof Select) { // Either LOOKUPSWITCH or TABLESWITCH
942                    final InstructionHandle[] targets = ((Select) b).getTargets();
943                    for (int j = 0; j < targets.length; j++) {
944                        if (targets[j] == oldTarget) {
945                            ((Select) b).setTarget(j, newTarget);
946                        }
947                    }
948                }
949            }
950        }
951    }
952
953    /**
954     * Redirect all references of exception handlers from oldTarget to newTarget.
955     *
956     * @param exceptions array of exception handlers
957     * @param oldTarget the old target instruction handle
958     * @param newTarget the new target instruction handle
959     * @see MethodGen
960     */
961    public void redirectExceptionHandlers(final CodeExceptionGen[] exceptions, final InstructionHandle oldTarget, final InstructionHandle newTarget) {
962        Streams.of(exceptions).forEach(exception -> {
963            if (exception.getStartPC() == oldTarget) {
964                exception.setStartPC(newTarget);
965            }
966            if (exception.getEndPC() == oldTarget) {
967                exception.setEndPC(newTarget);
968            }
969            if (exception.getHandlerPC() == oldTarget) {
970                exception.setHandlerPC(newTarget);
971            }
972        });
973    }
974
975    /**
976     * Redirect all references of local variables from oldTarget to newTarget.
977     *
978     * @param lg array of local variables
979     * @param oldTarget the old target instruction handle
980     * @param newTarget the new target instruction handle
981     * @see MethodGen
982     */
983    public void redirectLocalVariables(final LocalVariableGen[] lg, final InstructionHandle oldTarget, final InstructionHandle newTarget) {
984        Streams.of(lg).forEach(element -> {
985            if (element.getStart() == oldTarget) {
986                element.setStart(newTarget);
987            }
988            if (element.getEnd() == oldTarget) {
989                element.setEnd(newTarget);
990            }
991        });
992    }
993
994    /**
995     * Remove from instruction 'prev' to instruction 'next' both contained in this list. Throws TargetLostException when one
996     * of the removed instruction handles is still being targeted.
997     *
998     * @param prev where to start deleting (predecessor, exclusive)
999     * @param next where to end deleting (successor, exclusive)
1000     */
1001    private void remove(final InstructionHandle prev, InstructionHandle next) throws TargetLostException {
1002        InstructionHandle first;
1003        InstructionHandle last; // First and last deleted instruction
1004        if (prev == null && next == null) {
1005            first = start;
1006            last = end;
1007            start = end = null;
1008        } else {
1009            if (prev == null) { // At start of list
1010                first = start;
1011                start = next;
1012            } else {
1013                first = prev.getNext();
1014                prev.setNext(next);
1015            }
1016            if (next == null) { // At end of list
1017                last = end;
1018                end = prev;
1019            } else {
1020                last = next.getPrev();
1021                next.setPrev(prev);
1022            }
1023        }
1024        first.setPrev(null); // Completely separated from rest of list
1025        last.setNext(null);
1026        final List<InstructionHandle> targetList = new ArrayList<>();
1027        for (InstructionHandle ih = first; ih != null; ih = ih.getNext()) {
1028            ih.getInstruction().dispose(); // e.g. BranchInstructions release their targets
1029        }
1030        final StringBuilder buf = new StringBuilder("{ ");
1031        for (InstructionHandle ih = first; ih != null; ih = next) {
1032            next = ih.getNext();
1033            length--;
1034            if (ih.hasTargeters()) { // Still got targeters?
1035                targetList.add(ih);
1036                buf.append(ih.toString(true)).append(" ");
1037                ih.setNext(ih.setPrev(null));
1038            } else {
1039                ih.dispose();
1040            }
1041        }
1042        buf.append("}");
1043        if (!targetList.isEmpty()) {
1044            throw new TargetLostException(targetList.toArray(InstructionHandle.EMPTY_ARRAY), buf.toString());
1045        }
1046    }
1047
1048    /**
1049     * Remove observer for this object.
1050     */
1051    public void removeObserver(final InstructionListObserver o) {
1052        if (observers != null) {
1053            observers.remove(o);
1054        }
1055    }
1056
1057    /**
1058     * Replace all references to the old constant pool with references to the new constant pool
1059     */
1060    public void replaceConstantPool(final ConstantPoolGen oldCp, final ConstantPoolGen newCp) {
1061        for (InstructionHandle ih = start; ih != null; ih = ih.getNext()) {
1062            final Instruction i = ih.getInstruction();
1063            if (i instanceof CPInstruction) {
1064                final CPInstruction ci = (CPInstruction) i;
1065                final Constant c = oldCp.getConstant(ci.getIndex());
1066                ci.setIndex(newCp.addConstant(c, oldCp));
1067            }
1068        }
1069    }
1070
1071    public void setPositions() { // TODO could be package-protected? (some test code would need to be repackaged)
1072        setPositions(false);
1073    }
1074
1075    /**
1076     * Give all instructions their position number (offset in byte stream), i.e., make the list ready to be dumped.
1077     *
1078     * @param check Perform sanity checks, e.g. if all targeted instructions really belong to this list
1079     */
1080    public void setPositions(final boolean check) { // called by code in other packages
1081        int maxAdditionalBytes = 0;
1082        int additionalBytes = 0;
1083        int index = 0;
1084        int count = 0;
1085        final int[] pos = new int[length];
1086        /*
1087         * Pass 0: Sanity checks
1088         */
1089        if (check) {
1090            for (InstructionHandle ih = start; ih != null; ih = ih.getNext()) {
1091                final Instruction i = ih.getInstruction();
1092                if (i instanceof BranchInstruction) { // target instruction within list?
1093                    Instruction inst = ((BranchInstruction) i).getTarget().getInstruction();
1094                    if (!contains(inst)) {
1095                        throw new ClassGenException("Branch target of " + Const.getOpcodeName(i.getOpcode()) + ":" + inst + " not in instruction list");
1096                    }
1097                    if (i instanceof Select) {
1098                        final InstructionHandle[] targets = ((Select) i).getTargets();
1099                        for (final InstructionHandle target : targets) {
1100                            inst = target.getInstruction();
1101                            if (!contains(inst)) {
1102                                throw new ClassGenException("Branch target of " + Const.getOpcodeName(i.getOpcode()) + ":" + inst + " not in instruction list");
1103                            }
1104                        }
1105                    }
1106                    if (!(ih instanceof BranchHandle)) {
1107                        throw new ClassGenException(
1108                            "Branch instruction " + Const.getOpcodeName(i.getOpcode()) + ":" + inst + " not contained in BranchHandle.");
1109                    }
1110                }
1111            }
1112        }
1113        /*
1114         * Pass 1: Set position numbers and sum up the maximum number of bytes an instruction may be shifted.
1115         */
1116        for (InstructionHandle ih = start; ih != null; ih = ih.getNext()) {
1117            final Instruction i = ih.getInstruction();
1118            ih.setPosition(index);
1119            pos[count++] = index;
1120            /*
1121             * Gets an estimate about how many additional bytes may be added, because BranchInstructions may have variable length
1122             * depending on the target offset (short vs. int) or alignment issues (TABLESWITCH and LOOKUPSWITCH).
1123             */
1124            switch (i.getOpcode()) {
1125            case Const.JSR:
1126            case Const.GOTO:
1127                maxAdditionalBytes += 2;
1128                break;
1129            case Const.TABLESWITCH:
1130            case Const.LOOKUPSWITCH:
1131                maxAdditionalBytes += 3;
1132                break;
1133            default:
1134                // TODO should this be an error?
1135                break;
1136            }
1137            index += i.getLength();
1138        }
1139        /*
1140         * Pass 2: Expand the variable-length (Branch) Instructions depending on the target offset (short or int) and ensure that
1141         * branch targets are within this list.
1142         */
1143        for (InstructionHandle ih = start; ih != null; ih = ih.getNext()) {
1144            additionalBytes += ih.updatePosition(additionalBytes, maxAdditionalBytes);
1145        }
1146        /*
1147         * Pass 3: Update position numbers (which may have changed due to the preceding expansions), like pass 1.
1148         */
1149        index = count = 0;
1150        for (InstructionHandle ih = start; ih != null; ih = ih.getNext()) {
1151            final Instruction i = ih.getInstruction();
1152            ih.setPosition(index);
1153            pos[count++] = index;
1154            index += i.getLength();
1155        }
1156        bytePositions = Arrays.copyOfRange(pos, 0, count); // Trim to proper size
1157    }
1158
1159    /**
1160     * @return length of list (Number of instructions, not bytes)
1161     */
1162    public int size() {
1163        return length;
1164    }
1165
1166    @Override
1167    public String toString() {
1168        return toString(true);
1169    }
1170
1171    /**
1172     * @param verbose toggle output format
1173     * @return String containing all instructions in this list.
1174     */
1175    public String toString(final boolean verbose) {
1176        final StringBuilder buf = new StringBuilder();
1177        for (InstructionHandle ih = start; ih != null; ih = ih.getNext()) {
1178            buf.append(ih.toString(verbose)).append("\n");
1179        }
1180        return buf.toString();
1181    }
1182
1183    /**
1184     * Call notify() method on all observers. This method is not called automatically whenever the state has changed, but
1185     * has to be called by the user after he has finished editing the object.
1186     */
1187    public void update() {
1188        if (observers != null) {
1189            for (final InstructionListObserver observer : observers) {
1190                observer.notify(this);
1191            }
1192        }
1193    }
1194}