ASM: a very small and fast Java bytecode manipulation framework
Copyright (c) 2000-2011 INRIA, France Telecom
All rights reserved.
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modification, are permitted provided that the following conditions
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/***
 * ASM: a very small and fast Java bytecode manipulation framework
 * Copyright (c) 2000-2011 INRIA, France Telecom
 * 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. Neither the name of the copyright holders nor the names of its
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS 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 COPYRIGHT OWNER OR 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.
 */
package org.objectweb.asm.commons;

import java.util.AbstractMap;
import java.util.ArrayList;
import java.util.BitSet;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.objectweb.asm.Label;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.Type;
import org.objectweb.asm.tree.AbstractInsnNode;
import org.objectweb.asm.tree.InsnList;
import org.objectweb.asm.tree.InsnNode;
import org.objectweb.asm.tree.JumpInsnNode;
import org.objectweb.asm.tree.LabelNode;
import org.objectweb.asm.tree.LocalVariableNode;
import org.objectweb.asm.tree.LookupSwitchInsnNode;
import org.objectweb.asm.tree.MethodNode;
import org.objectweb.asm.tree.TableSwitchInsnNode;
import org.objectweb.asm.tree.TryCatchBlockNode;

A MethodVisitor that removes JSR instructions and inlines the referenced subroutines. Explanation of how it works TODO
Author:
Niko Matsakis/**
 * A {@link org.objectweb.asm.MethodVisitor} that removes JSR instructions and
 * inlines the referenced subroutines.
 * 
 * <b>Explanation of how it works</b> TODO
 * 
 * @author Niko Matsakis
 */
public class JSRInlinerAdapter extends MethodNode implements Opcodes {

    private static final boolean LOGGING = false;

    
For each label that is jumped to by a JSR, we create a BitSet instance.
/**
     * For each label that is jumped to by a JSR, we create a BitSet instance.
     */
    private final Map<LabelNode, BitSet> subroutineHeads = new HashMap<LabelNode, BitSet>();

    
This subroutine instance denotes the line of execution that is not
contained within any subroutine; i.e., the "subroutine" that is executing
when a method first begins.
/**
     * This subroutine instance denotes the line of execution that is not
     * contained within any subroutine; i.e., the "subroutine" that is executing
     * when a method first begins.
     */
    private final BitSet mainSubroutine = new BitSet();

    
This BitSet contains the index of every instruction that belongs to more
than one subroutine. This should not happen often.
/**
     * This BitSet contains the index of every instruction that belongs to more
     * than one subroutine. This should not happen often.
     */
    final BitSet dualCitizens = new BitSet();

    
Creates a new JSRInliner. Subclasses must not use this
constructor. Instead, they must use the JSRInlinerAdapter(int, MethodVisitor, int, String, String, String, String[]) version. 
Params:
mv – 
           the MethodVisitor to send the resulting inlined
           method code to (use null for none).
access –  the method's access flags (see Opcodes). This parameter also indicates if the method is synthetic and/or deprecated.
name – 
           the method's name.
desc –  the method's descriptor (see Type).
signature – 
           the method's signature. May be null.
exceptions –  the internal names of the method's exception classes (see getInternalName). May be null.
Throws:
IllegalStateException – 
            If a subclass calls this constructor./**
     * Creates a new JSRInliner. <i>Subclasses must not use this
     * constructor</i>. Instead, they must use the
     * {@link #JSRInlinerAdapter(int, MethodVisitor, int, String, String, String, String[])}
     * version.
     * 
     * @param mv
     *            the <code>MethodVisitor</code> to send the resulting inlined
     *            method code to (use <code>null</code> for none).
     * @param access
     *            the method's access flags (see {@link Opcodes}). This
     *            parameter also indicates if the method is synthetic and/or
     *            deprecated.
     * @param name
     *            the method's name.
     * @param desc
     *            the method's descriptor (see {@link Type}).
     * @param signature
     *            the method's signature. May be <tt>null</tt>.
     * @param exceptions
     *            the internal names of the method's exception classes (see
     *            {@link Type#getInternalName() getInternalName}). May be
     *            <tt>null</tt>.
     * @throws IllegalStateException
     *             If a subclass calls this constructor.
     */
    public JSRInlinerAdapter(final MethodVisitor mv, final int access,
            final String name, final String desc, final String signature,
            final String[] exceptions) {
        this(Opcodes.ASM5, mv, access, name, desc, signature, exceptions);
        if (getClass() != JSRInlinerAdapter.class) {
            throw new IllegalStateException();
        }
    }

    
Creates a new JSRInliner.
Params:
api –  the ASM API version implemented by this visitor. Must be one of Opcodes.ASM4 or Opcodes.ASM5.
mv – 
           the MethodVisitor to send the resulting inlined
           method code to (use null for none).
access –  the method's access flags (see Opcodes). This parameter also indicates if the method is synthetic and/or deprecated.
name – 
           the method's name.
desc –  the method's descriptor (see Type).
signature – 
           the method's signature. May be null.
exceptions –  the internal names of the method's exception classes (see getInternalName). May be null./**
     * Creates a new JSRInliner.
     * 
     * @param api
     *            the ASM API version implemented by this visitor. Must be one
     *            of {@link Opcodes#ASM4} or {@link Opcodes#ASM5}.
     * @param mv
     *            the <code>MethodVisitor</code> to send the resulting inlined
     *            method code to (use <code>null</code> for none).
     * @param access
     *            the method's access flags (see {@link Opcodes}). This
     *            parameter also indicates if the method is synthetic and/or
     *            deprecated.
     * @param name
     *            the method's name.
     * @param desc
     *            the method's descriptor (see {@link Type}).
     * @param signature
     *            the method's signature. May be <tt>null</tt>.
     * @param exceptions
     *            the internal names of the method's exception classes (see
     *            {@link Type#getInternalName() getInternalName}). May be
     *            <tt>null</tt>.
     */
    protected JSRInlinerAdapter(final int api, final MethodVisitor mv,
            final int access, final String name, final String desc,
            final String signature, final String[] exceptions) {
        super(api, access, name, desc, signature, exceptions);
        this.mv = mv;
    }

    
Detects a JSR instruction and sets a flag to indicate we will need to do
inlining.
/**
     * Detects a JSR instruction and sets a flag to indicate we will need to do
     * inlining.
     */
    @Override
    public void visitJumpInsn(final int opcode, final Label lbl) {
        super.visitJumpInsn(opcode, lbl);
        LabelNode ln = ((JumpInsnNode) instructions.getLast()).label;
        if (opcode == JSR && !subroutineHeads.containsKey(ln)) {
            subroutineHeads.put(ln, new BitSet());
        }
    }

    
If any JSRs were seen, triggers the inlining process. Otherwise, forwards
the byte codes untouched.
/**
     * If any JSRs were seen, triggers the inlining process. Otherwise, forwards
     * the byte codes untouched.
     */
    @Override
    public void visitEnd() {
        if (!subroutineHeads.isEmpty()) {
            markSubroutines();
            if (LOGGING) {
                log(mainSubroutine.toString());
                Iterator<BitSet> it = subroutineHeads.values().iterator();
                while (it.hasNext()) {
                    BitSet sub = it.next();
                    log(sub.toString());
                }
            }
            emitCode();
        }

        // Forward the translate opcodes on if appropriate:
        if (mv != null) {
            accept(mv);
        }
    }

    
Walks the method and determines which internal subroutine(s), if any,
each instruction is a method of.
/**
     * Walks the method and determines which internal subroutine(s), if any,
     * each instruction is a method of.
     */
    private void markSubroutines() {
        BitSet anyvisited = new BitSet();

        // First walk the main subroutine and find all those instructions which
        // can be reached without invoking any JSR at all
        markSubroutineWalk(mainSubroutine, 0, anyvisited);

        // Go through the head of each subroutine and find any nodes reachable
        // to that subroutine without following any JSR links.
        for (Iterator<Map.Entry<LabelNode, BitSet>> it = subroutineHeads
                .entrySet().iterator(); it.hasNext();) {
            Map.Entry<LabelNode, BitSet> entry = it.next();
            LabelNode lab = entry.getKey();
            BitSet sub = entry.getValue();
            int index = instructions.indexOf(lab);
            markSubroutineWalk(sub, index, anyvisited);
        }
    }

    
Performs a depth first search walking the normal byte code path starting
at index, and adding each instruction encountered into the
subroutine sub. After this walk is complete, iterates over
the exception handlers to ensure that we also include those byte codes
which are reachable through an exception that may be thrown during the
execution of the subroutine. Invoked from markSubroutines().
Params:
sub – 
           the subroutine whose instructions must be computed.
index – 
           an instruction of this subroutine.
anyvisited – 
           indexes of the already visited instructions, i.e. marked as
           part of this subroutine or any previously computed subroutine./**
     * Performs a depth first search walking the normal byte code path starting
     * at <code>index</code>, and adding each instruction encountered into the
     * subroutine <code>sub</code>. After this walk is complete, iterates over
     * the exception handlers to ensure that we also include those byte codes
     * which are reachable through an exception that may be thrown during the
     * execution of the subroutine. Invoked from <code>markSubroutines()</code>.
     * 
     * @param sub
     *            the subroutine whose instructions must be computed.
     * @param index
     *            an instruction of this subroutine.
     * @param anyvisited
     *            indexes of the already visited instructions, i.e. marked as
     *            part of this subroutine or any previously computed subroutine.
     */
    private void markSubroutineWalk(final BitSet sub, final int index,
            final BitSet anyvisited) {
        if (LOGGING) {
            log("markSubroutineWalk: sub=" + sub + " index=" + index);
        }

        // First find those instructions reachable via normal execution
        markSubroutineWalkDFS(sub, index, anyvisited);

        // Now, make sure we also include any applicable exception handlers
        boolean loop = true;
        while (loop) {
            loop = false;
            for (Iterator<TryCatchBlockNode> it = tryCatchBlocks.iterator(); it
                    .hasNext();) {
                TryCatchBlockNode trycatch = it.next();

                if (LOGGING) {
                    // TODO use of default toString().
                    log("Scanning try/catch " + trycatch);
                }

                // If the handler has already been processed, skip it.
                int handlerindex = instructions.indexOf(trycatch.handler);
                if (sub.get(handlerindex)) {
                    continue;
                }

                int startindex = instructions.indexOf(trycatch.start);
                int endindex = instructions.indexOf(trycatch.end);
                int nextbit = sub.nextSetBit(startindex);
                if (nextbit != -1 && nextbit < endindex) {
                    if (LOGGING) {
                        log("Adding exception handler: " + startindex + '-'
                                + endindex + " due to " + nextbit + " handler "
                                + handlerindex);
                    }
                    markSubroutineWalkDFS(sub, handlerindex, anyvisited);
                    loop = true;
                }
            }
        }
    }

    
Performs a simple DFS of the instructions, assigning each to the
subroutine sub. Starts from index. Invoked only
by markSubroutineWalk().
Params:
sub – 
           the subroutine whose instructions must be computed.
index – 
           an instruction of this subroutine.
anyvisited – 
           indexes of the already visited instructions, i.e. marked as
           part of this subroutine or any previously computed subroutine./**
     * Performs a simple DFS of the instructions, assigning each to the
     * subroutine <code>sub</code>. Starts from <code>index</code>. Invoked only
     * by <code>markSubroutineWalk()</code>.
     * 
     * @param sub
     *            the subroutine whose instructions must be computed.
     * @param index
     *            an instruction of this subroutine.
     * @param anyvisited
     *            indexes of the already visited instructions, i.e. marked as
     *            part of this subroutine or any previously computed subroutine.
     */
    private void markSubroutineWalkDFS(final BitSet sub, int index,
            final BitSet anyvisited) {
        while (true) {
            AbstractInsnNode node = instructions.get(index);

            // don't visit a node twice
            if (sub.get(index)) {
                return;
            }
            sub.set(index);

            // check for those nodes already visited by another subroutine
            if (anyvisited.get(index)) {
                dualCitizens.set(index);
                if (LOGGING) {
                    log("Instruction #" + index + " is dual citizen.");
                }
            }
            anyvisited.set(index);

            if (node.getType() == AbstractInsnNode.JUMP_INSN
                    && node.getOpcode() != JSR) {
                // we do not follow recursively called subroutines here; but any
                // other sort of branch we do follow
                JumpInsnNode jnode = (JumpInsnNode) node;
                int destidx = instructions.indexOf(jnode.label);
                markSubroutineWalkDFS(sub, destidx, anyvisited);
            }
            if (node.getType() == AbstractInsnNode.TABLESWITCH_INSN) {
                TableSwitchInsnNode tsnode = (TableSwitchInsnNode) node;
                int destidx = instructions.indexOf(tsnode.dflt);
                markSubroutineWalkDFS(sub, destidx, anyvisited);
                for (int i = tsnode.labels.size() - 1; i >= 0; --i) {
                    LabelNode l = tsnode.labels.get(i);
                    destidx = instructions.indexOf(l);
                    markSubroutineWalkDFS(sub, destidx, anyvisited);
                }
            }
            if (node.getType() == AbstractInsnNode.LOOKUPSWITCH_INSN) {
                LookupSwitchInsnNode lsnode = (LookupSwitchInsnNode) node;
                int destidx = instructions.indexOf(lsnode.dflt);
                markSubroutineWalkDFS(sub, destidx, anyvisited);
                for (int i = lsnode.labels.size() - 1; i >= 0; --i) {
                    LabelNode l = lsnode.labels.get(i);
                    destidx = instructions.indexOf(l);
                    markSubroutineWalkDFS(sub, destidx, anyvisited);
                }
            }

            // check to see if this opcode falls through to the next instruction
            // or not; if not, return.
            switch (instructions.get(index).getOpcode()) {
            case GOTO:
            case RET:
            case TABLESWITCH:
            case LOOKUPSWITCH:
            case IRETURN:
            case LRETURN:
            case FRETURN:
            case DRETURN:
            case ARETURN:
            case RETURN:
            case ATHROW:
                /*
                 * note: this either returns from this subroutine, or a parent
                 * subroutine which invoked it
                 */
                return;
            }

            // Use tail recursion here in the form of an outer while loop to
            // avoid our stack growing needlessly:
            index++;

            // We implicitly assumed above that execution can always fall
            // through to the next instruction after a JSR. But a subroutine may
            // never return, in which case the code after the JSR is unreachable
            // and can be anything. In particular, it can seem to fall off the
            // end of the method, so we must handle this case here (we could
            // instead detect whether execution can return or not from a JSR,
            // but this is more complicated).
            if (index >= instructions.size()) {
                return;
            }
        }
    }

    
Creates the new instructions, inlining each instantiation of each
subroutine until the code is fully elaborated.
/**
     * Creates the new instructions, inlining each instantiation of each
     * subroutine until the code is fully elaborated.
     */
    private void emitCode() {
        LinkedList<Instantiation> worklist = new LinkedList<Instantiation>();
        // Create an instantiation of the "root" subroutine, which is just the
        // main routine
        worklist.add(new Instantiation(null, mainSubroutine));

        // Emit instantiations of each subroutine we encounter, including the
        // main subroutine
        InsnList newInstructions = new InsnList();
        List<TryCatchBlockNode> newTryCatchBlocks = new ArrayList<TryCatchBlockNode>();
        List<LocalVariableNode> newLocalVariables = new ArrayList<LocalVariableNode>();
        while (!worklist.isEmpty()) {
            Instantiation inst = worklist.removeFirst();
            emitSubroutine(inst, worklist, newInstructions, newTryCatchBlocks,
                    newLocalVariables);
        }
        instructions = newInstructions;
        tryCatchBlocks = newTryCatchBlocks;
        localVariables = newLocalVariables;
    }

    
Emits one instantiation of one subroutine, specified by
instant. May add new instantiations that are invoked by this
one to the worklist parameter, and new try/catch blocks to
newTryCatchBlocks.
Params:
instant – 
           the instantiation that must be performed.
worklist – 
           list of the instantiations that remain to be done.
newInstructions – 
           the instruction list to which the instantiated code must be
           appended.
newTryCatchBlocks – 
           the exception handler list to which the instantiated handlers
           must be appended./**
     * Emits one instantiation of one subroutine, specified by
     * <code>instant</code>. May add new instantiations that are invoked by this
     * one to the <code>worklist</code> parameter, and new try/catch blocks to
     * <code>newTryCatchBlocks</code>.
     * 
     * @param instant
     *            the instantiation that must be performed.
     * @param worklist
     *            list of the instantiations that remain to be done.
     * @param newInstructions
     *            the instruction list to which the instantiated code must be
     *            appended.
     * @param newTryCatchBlocks
     *            the exception handler list to which the instantiated handlers
     *            must be appended.
     */
    private void emitSubroutine(final Instantiation instant,
            final List<Instantiation> worklist, final InsnList newInstructions,
            final List<TryCatchBlockNode> newTryCatchBlocks,
            final List<LocalVariableNode> newLocalVariables) {
        LabelNode duplbl = null;

        if (LOGGING) {
            log("--------------------------------------------------------");
            log("Emitting instantiation of subroutine " + instant.subroutine);
        }

        // Emit the relevant instructions for this instantiation, translating
        // labels and jump targets as we go:
        for (int i = 0, c = instructions.size(); i < c; i++) {
            AbstractInsnNode insn = instructions.get(i);
            Instantiation owner = instant.findOwner(i);

            // Always remap labels:
            if (insn.getType() == AbstractInsnNode.LABEL) {
                // Translate labels into their renamed equivalents.
                // Avoid adding the same label more than once. Note
                // that because we own this instruction the gotoTable
                // and the rangeTable will always agree.
                LabelNode ilbl = (LabelNode) insn;
                LabelNode remap = instant.rangeLabel(ilbl);
                if (LOGGING) {
                    // TODO use of default toString().
                    log("Translating lbl #" + i + ':' + ilbl + " to " + remap);
                }
                if (remap != duplbl) {
                    newInstructions.add(remap);
                    duplbl = remap;
                }
                continue;
            }

            // We don't want to emit instructions that were already
            // emitted by a subroutine higher on the stack. Note that
            // it is still possible for a given instruction to be
            // emitted twice because it may belong to two subroutines
            // that do not invoke each other.
            if (owner != instant) {
                continue;
            }

            if (LOGGING) {
                log("Emitting inst #" + i);
            }

            if (insn.getOpcode() == RET) {
                // Translate RET instruction(s) to a jump to the return label
                // for the appropriate instantiation. The problem is that the
                // subroutine may "fall through" to the ret of a parent
                // subroutine; therefore, to find the appropriate ret label we
                // find the lowest subroutine on the stack that claims to own
                // this instruction. See the class javadoc comment for an
                // explanation on why this technique is safe (note: it is only
                // safe if the input is verifiable).
                LabelNode retlabel = null;
                for (Instantiation p = instant; p != null; p = p.previous) {
                    if (p.subroutine.get(i)) {
                        retlabel = p.returnLabel;
                    }
                }
                if (retlabel == null) {
                    // This is only possible if the mainSubroutine owns a RET
                    // instruction, which should never happen for verifiable
                    // code.
                    throw new RuntimeException("Instruction #" + i
                            + " is a RET not owned by any subroutine");
                }
                newInstructions.add(new JumpInsnNode(GOTO, retlabel));
            } else if (insn.getOpcode() == JSR) {
                LabelNode lbl = ((JumpInsnNode) insn).label;
                BitSet sub = subroutineHeads.get(lbl);
                Instantiation newinst = new Instantiation(instant, sub);
                LabelNode startlbl = newinst.gotoLabel(lbl);

                if (LOGGING) {
                    log(" Creating instantiation of subr " + sub);
                }

                // Rather than JSRing, we will jump to the inline version and
                // push NULL for what was once the return value. This hack
                // allows us to avoid doing any sort of data flow analysis to
                // figure out which instructions manipulate the old return value
                // pointer which is now known to be unneeded.
                newInstructions.add(new InsnNode(ACONST_NULL));
                newInstructions.add(new JumpInsnNode(GOTO, startlbl));
                newInstructions.add(newinst.returnLabel);

                // Insert this new instantiation into the queue to be emitted
                // later.
                worklist.add(newinst);
            } else {
                newInstructions.add(insn.clone(instant));
            }
        }

        // Emit try/catch blocks that are relevant to this method.
        for (Iterator<TryCatchBlockNode> it = tryCatchBlocks.iterator(); it
                .hasNext();) {
            TryCatchBlockNode trycatch = it.next();

            if (LOGGING) {
                // TODO use of default toString().
                log("try catch block original labels=" + trycatch.start + '-'
                        + trycatch.end + "->" + trycatch.handler);
            }

            final LabelNode start = instant.rangeLabel(trycatch.start);
            final LabelNode end = instant.rangeLabel(trycatch.end);

            // Ignore empty try/catch regions
            if (start == end) {
                if (LOGGING) {
                    log(" try catch block empty in this subroutine");
                }
                continue;
            }

            final LabelNode handler = instant.gotoLabel(trycatch.handler);

            if (LOGGING) {
                // TODO use of default toString().
                log(" try catch block new labels=" + start + '-' + end + "->"
                        + handler);
            }

            if (start == null || end == null || handler == null) {
                throw new RuntimeException("Internal error!");
            }

            newTryCatchBlocks.add(new TryCatchBlockNode(start, end, handler,
                    trycatch.type));
        }

        for (Iterator<LocalVariableNode> it = localVariables.iterator(); it
                .hasNext();) {
            LocalVariableNode lvnode = it.next();
            if (LOGGING) {
                log("local var " + lvnode.name);
            }
            final LabelNode start = instant.rangeLabel(lvnode.start);
            final LabelNode end = instant.rangeLabel(lvnode.end);
            if (start == end) {
                if (LOGGING) {
                    log("  local variable empty in this sub");
                }
                continue;
            }
            newLocalVariables.add(new LocalVariableNode(lvnode.name,
                    lvnode.desc, lvnode.signature, start, end, lvnode.index));
        }
    }

    private static void log(final String str) {
        System.err.println(str);
    }

    
A class that represents an instantiation of a subroutine. Each
instantiation has an associate "stack" --- which is a listing of those
instantiations that were active when this particular instance of this
subroutine was invoked. Each instantiation also has a map from the
original labels of the program to the labels appropriate for this
instantiation, and finally a label to return to.
/**
     * A class that represents an instantiation of a subroutine. Each
     * instantiation has an associate "stack" --- which is a listing of those
     * instantiations that were active when this particular instance of this
     * subroutine was invoked. Each instantiation also has a map from the
     * original labels of the program to the labels appropriate for this
     * instantiation, and finally a label to return to.
     */
    private class Instantiation extends AbstractMap<LabelNode, LabelNode> {

        
Previous instantiations; the stack must be statically predictable to
be inlinable.
/**
         * Previous instantiations; the stack must be statically predictable to
         * be inlinable.
         */
        final Instantiation previous;

        
The subroutine this is an instantiation of.
/**
         * The subroutine this is an instantiation of.
         */
        public final BitSet subroutine;

        
This table maps Labels from the original source to Labels pointing at
code specific to this instantiation, for use in remapping try/catch
blocks,as well as gotos.
Note that in the presence of dual citizens instructions, that is,
instructions which belong to more than one subroutine due to the
merging of control flow without a RET instruction, we will map the
target label of a GOTO to the label used by the instantiation lowest
on the stack. This avoids code duplication during inlining in most
cases.
See Also:
findOwner(int)/**
         * This table maps Labels from the original source to Labels pointing at
         * code specific to this instantiation, for use in remapping try/catch
         * blocks,as well as gotos.
         * 
         * Note that in the presence of dual citizens instructions, that is,
         * instructions which belong to more than one subroutine due to the
         * merging of control flow without a RET instruction, we will map the
         * target label of a GOTO to the label used by the instantiation lowest
         * on the stack. This avoids code duplication during inlining in most
         * cases.
         * 
         * @see #findOwner(int)
         */
        public final Map<LabelNode, LabelNode> rangeTable = new HashMap<LabelNode, LabelNode>();

        
All returns for this instantiation will be mapped to this label
/**
         * All returns for this instantiation will be mapped to this label
         */
        public final LabelNode returnLabel;

        Instantiation(final Instantiation prev, final BitSet sub) {
            previous = prev;
            subroutine = sub;
            for (Instantiation p = prev; p != null; p = p.previous) {
                if (p.subroutine == sub) {
                    throw new RuntimeException("Recursive invocation of " + sub);
                }
            }

            // Determine the label to return to when this subroutine terminates
            // via RET: note that the main subroutine never terminates via RET.
            if (prev != null) {
                returnLabel = new LabelNode();
            } else {
                returnLabel = null;
            }

            // Each instantiation will remap the labels from the code above to
            // refer to its particular copy of its own instructions. Note that
            // we collapse labels which point at the same instruction into one:
            // this is fairly common as we are often ignoring large chunks of
            // instructions, so what were previously distinct labels become
            // duplicates.
            LabelNode duplbl = null;
            for (int i = 0, c = instructions.size(); i < c; i++) {
                AbstractInsnNode insn = instructions.get(i);

                if (insn.getType() == AbstractInsnNode.LABEL) {
                    LabelNode ilbl = (LabelNode) insn;

                    if (duplbl == null) {
                        // if we already have a label pointing at this spot,
                        // don't recreate it.
                        duplbl = new LabelNode();
                    }

                    // Add an entry in the rangeTable for every label
                    // in the original code which points at the next
                    // instruction of our own to be emitted.
                    rangeTable.put(ilbl, duplbl);
                } else if (findOwner(i) == this) {
                    // We will emit this instruction, so clear the 'duplbl' flag
                    // since the next Label will refer to a distinct
                    // instruction.
                    duplbl = null;
                }
            }
        }

        
Returns the "owner" of a particular instruction relative to this
instantiation: the owner referes to the Instantiation which will emit
the version of this instruction that we will execute.
Typically, the return value is either this or
null. this indicates that this
instantiation will generate the version of this instruction that we
will execute, and null indicates that this instantiation
never executes the given instruction.
Sometimes, however, an instruction can belong to multiple
subroutines; this is called a "dual citizen" instruction (though it
may belong to more than 2 subroutines), and occurs when multiple
subroutines branch to common points of control. In this case, the
owner is the subroutine that appears lowest on the stack, and which
also owns the instruction in question.
Params:
i – 
           the index of the instruction in the original code
Returns:
the "owner" of a particular instruction relative to this
        instantiation./**
         * Returns the "owner" of a particular instruction relative to this
         * instantiation: the owner referes to the Instantiation which will emit
         * the version of this instruction that we will execute.
         * 
         * Typically, the return value is either <code>this</code> or
         * <code>null</code>. <code>this</code> indicates that this
         * instantiation will generate the version of this instruction that we
         * will execute, and <code>null</code> indicates that this instantiation
         * never executes the given instruction.
         * 
         * Sometimes, however, an instruction can belong to multiple
         * subroutines; this is called a "dual citizen" instruction (though it
         * may belong to more than 2 subroutines), and occurs when multiple
         * subroutines branch to common points of control. In this case, the
         * owner is the subroutine that appears lowest on the stack, and which
         * also owns the instruction in question.
         * 
         * @param i
         *            the index of the instruction in the original code
         * @return the "owner" of a particular instruction relative to this
         *         instantiation.
         */
        public Instantiation findOwner(final int i) {
            if (!subroutine.get(i)) {
                return null;
            }
            if (!dualCitizens.get(i)) {
                return this;
            }
            Instantiation own = this;
            for (Instantiation p = previous; p != null; p = p.previous) {
                if (p.subroutine.get(i)) {
                    own = p;
                }
            }
            return own;
        }

        
Looks up the label l in the gotoTable, thus
translating it from a Label in the original code, to a Label in the
inlined code that is appropriate for use by an instruction that
branched to the original label.
Params:
l – 
           The label we will be translating
See Also:
rangeLabel
Returns:
a label for use by a branch instruction in the inlined code/**
         * Looks up the label <code>l</code> in the <code>gotoTable</code>, thus
         * translating it from a Label in the original code, to a Label in the
         * inlined code that is appropriate for use by an instruction that
         * branched to the original label.
         * 
         * @param l
         *            The label we will be translating
         * @return a label for use by a branch instruction in the inlined code
         * @see #rangeLabel
         */
        public LabelNode gotoLabel(final LabelNode l) {
            // owner should never be null, because owner is only null
            // if an instruction cannot be reached from this subroutine
            Instantiation owner = findOwner(instructions.indexOf(l));
            return owner.rangeTable.get(l);
        }

        
Looks up the label l in the rangeTable,
thus translating it from a Label in the original code, to a Label in
the inlined code that is appropriate for use by an try/catch or
variable use annotation.
Params:
l – 
           The label we will be translating
See Also:
rangeTable
Returns:
a label for use by a try/catch or variable annotation in the
        original code/**
         * Looks up the label <code>l</code> in the <code>rangeTable</code>,
         * thus translating it from a Label in the original code, to a Label in
         * the inlined code that is appropriate for use by an try/catch or
         * variable use annotation.
         * 
         * @param l
         *            The label we will be translating
         * @return a label for use by a try/catch or variable annotation in the
         *         original code
         * @see #rangeTable
         */
        public LabelNode rangeLabel(final LabelNode l) {
            return rangeTable.get(l);
        }

        // AbstractMap implementation

        @Override
        public Set<Map.Entry<LabelNode, LabelNode>> entrySet() {
            return null;
        }

        @Override
        public LabelNode get(final Object o) {
            return gotoLabel((LabelNode) o);
        }
    }
}