java/17 : java.base/jdk/internal/org/objectweb/asm/commons/JSRInlinerAdapter.java

JSRInlinerAdapter
https://openjdk.java.net/
GPLv2 + Classpath Exception
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 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
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 *
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/*
 * This file is available under and governed by the GNU General Public
 * License version 2 only, as published by the Free Software Foundation.
 * However, the following notice accompanied the original version of this
 * file:
 *
 * 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
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 * 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
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package jdk.internal.org.objectweb.asm.commons;

import java.util.AbstractMap;
import java.util.ArrayList;
import java.util.BitSet;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import jdk.internal.org.objectweb.asm.Label;
import jdk.internal.org.objectweb.asm.MethodVisitor;
import jdk.internal.org.objectweb.asm.Opcodes;
import jdk.internal.org.objectweb.asm.tree.AbstractInsnNode;
import jdk.internal.org.objectweb.asm.tree.InsnList;
import jdk.internal.org.objectweb.asm.tree.InsnNode;
import jdk.internal.org.objectweb.asm.tree.JumpInsnNode;
import jdk.internal.org.objectweb.asm.tree.LabelNode;
import jdk.internal.org.objectweb.asm.tree.LocalVariableNode;
import jdk.internal.org.objectweb.asm.tree.LookupSwitchInsnNode;
import jdk.internal.org.objectweb.asm.tree.MethodNode;
import jdk.internal.org.objectweb.asm.tree.TableSwitchInsnNode;
import jdk.internal.org.objectweb.asm.tree.TryCatchBlockNode;

A MethodVisitor that removes JSR instructions and inlines the referenced subroutines. 
Author: Niko Matsakis/**
 * A {@link jdk.internal.org.objectweb.asm.MethodVisitor} that removes JSR instructions and inlines the
 * referenced subroutines.
 *
 * @author Niko Matsakis
 */
// DontCheck(AbbreviationAsWordInName): can't be renamed (for backward binary compatibility).
public class JSRInlinerAdapter extends MethodNode implements Opcodes {

    The instructions that belong to the main "subroutine". Bit i is set iff instruction at index i
belongs to this main "subroutine".
/**
      * The instructions that belong to the main "subroutine". Bit i is set iff instruction at index i
      * belongs to this main "subroutine".
      */
    private final BitSet mainSubroutineInsns = new BitSet();

    The instructions that belong to each subroutine. For each label which is the target of a JSR
instruction, bit i of the corresponding BitSet in this map is set iff instruction at index i
belongs to this subroutine.
/**
      * The instructions that belong to each subroutine. For each label which is the target of a JSR
      * instruction, bit i of the corresponding BitSet in this map is set iff instruction at index i
      * belongs to this subroutine.
      */
    private final Map<LabelNode, BitSet> subroutinesInsns = new HashMap<>();

    The instructions that belong to more that one subroutine. Bit i is set iff instruction at index
i belongs to more than one subroutine.
/**
      * The instructions that belong to more that one subroutine. Bit i is set iff instruction at index
      * i belongs to more than one subroutine.
      */
    final BitSet sharedSubroutineInsns = new BitSet();

    Constructs a new JSRInlinerAdapter. Subclasses must not use this constructor. Instead, they must use the JSRInlinerAdapter(int, MethodVisitor, int, String, String, String, String[]) version. 
Params: methodVisitor – the method visitor to send the resulting inlined method code to, or 
    null.
access – the method's access flags.
name – the method's name.
descriptor – the method's descriptor.
signature – the method's signature. May be null.
exceptions – the internal names of the method's exception classes. May be null.
Throws: IllegalStateException – if a subclass calls this constructor./**
      * Constructs a new {@link JSRInlinerAdapter}. <i>Subclasses must not use this constructor</i>.
      * Instead, they must use the {@link #JSRInlinerAdapter(int, MethodVisitor, int, String, String,
      * String, String[])} version.
      *
      * @param methodVisitor the method visitor to send the resulting inlined method code to, or <code>
      *     null</code>.
      * @param access the method's access flags.
      * @param name the method's name.
      * @param descriptor the method's descriptor.
      * @param signature the method's signature. May be {@literal null}.
      * @param exceptions the internal names of the method's exception classes. May be {@literal null}.
      * @throws IllegalStateException if a subclass calls this constructor.
      */
    public JSRInlinerAdapter(
            final MethodVisitor methodVisitor,
            final int access,
            final String name,
            final String descriptor,
            final String signature,
            final String[] exceptions) {
        this(
                /* latest api = */ Opcodes.ASM8,
                methodVisitor,
                access,
                name,
                descriptor,
                signature,
                exceptions);
        if (getClass() != JSRInlinerAdapter.class) {
            throw new IllegalStateException();
        }
    }

    Constructs a new JSRInlinerAdapter. 
Params: api – the ASM API version implemented by this visitor. Must be one of Opcodes.ASM4, Opcodes.ASM5, Opcodes.ASM6, Opcodes.ASM7 or Opcodes.ASM8.
methodVisitor – the method visitor to send the resulting inlined method code to, or 
    null.
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.
descriptor – the method's descriptor.
signature – the method's signature. May be null.
exceptions – the internal names of the method's exception classes. May be null./**
      * Constructs a new {@link JSRInlinerAdapter}.
      *
      * @param api the ASM API version implemented by this visitor. Must be one of {@link
      *     Opcodes#ASM4}, {@link Opcodes#ASM5}, {@link Opcodes#ASM6}, {@link Opcodes#ASM7} or {@link
      *     Opcodes#ASM8}.
      * @param methodVisitor the method visitor to send the resulting inlined method code to, or <code>
      *     null</code>.
      * @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 descriptor the method's descriptor.
      * @param signature the method's signature. May be {@literal null}.
      * @param exceptions the internal names of the method's exception classes. May be {@literal null}.
      */
    protected JSRInlinerAdapter(
            final int api,
            final MethodVisitor methodVisitor,
            final int access,
            final String name,
            final String descriptor,
            final String signature,
            final String[] exceptions) {
        super(api, access, name, descriptor, signature, exceptions);
        this.mv = methodVisitor;
    }

    @Override
    public void visitJumpInsn(final int opcode, final Label label) {
        super.visitJumpInsn(opcode, label);
        LabelNode labelNode = ((JumpInsnNode) instructions.getLast()).label;
        if (opcode == JSR && !subroutinesInsns.containsKey(labelNode)) {
            subroutinesInsns.put(labelNode, new BitSet());
        }
    }

    @Override
    public void visitEnd() {
        if (!subroutinesInsns.isEmpty()) {
            // If the code contains at least one JSR instruction, inline the subroutines.
            findSubroutinesInsns();
            emitCode();
        }
        if (mv != null) {
            accept(mv);
        }
    }

    Determines, for each instruction, to which subroutine(s) it belongs. /** Determines, for each instruction, to which subroutine(s) it belongs. */
    private void findSubroutinesInsns() {
        // Find the instructions that belong to main subroutine.
        BitSet visitedInsns = new BitSet();
        findSubroutineInsns(0, mainSubroutineInsns, visitedInsns);
        // For each subroutine, find the instructions that belong to this subroutine.
        for (Map.Entry<LabelNode, BitSet> entry : subroutinesInsns.entrySet()) {
            LabelNode jsrLabelNode = entry.getKey();
            BitSet subroutineInsns = entry.getValue();
            findSubroutineInsns(instructions.indexOf(jsrLabelNode), subroutineInsns, visitedInsns);
        }
    }

    Finds the instructions that belong to the subroutine starting at the given instruction index.
For this the control flow graph is visited with a depth first search (this includes the normal
control flow and the exception handlers).
Params: startInsnIndex – the index of the first instruction of the subroutine.
subroutineInsns – where the indices of the instructions of the subroutine must be stored.
visitedInsns – the indices of the instructions that have been visited so far (including in
    previous calls to this method). This bitset is updated by this method each time a new
    instruction is visited. It is used to make sure each instruction is visited at most once./**
      * Finds the instructions that belong to the subroutine starting at the given instruction index.
      * For this the control flow graph is visited with a depth first search (this includes the normal
      * control flow and the exception handlers).
      *
      * @param startInsnIndex the index of the first instruction of the subroutine.
      * @param subroutineInsns where the indices of the instructions of the subroutine must be stored.
      * @param visitedInsns the indices of the instructions that have been visited so far (including in
      *     previous calls to this method). This bitset is updated by this method each time a new
      *     instruction is visited. It is used to make sure each instruction is visited at most once.
      */
    private void findSubroutineInsns(
            final int startInsnIndex, final BitSet subroutineInsns, final BitSet visitedInsns) {
        // First find the instructions reachable via normal execution.
        findReachableInsns(startInsnIndex, subroutineInsns, visitedInsns);

        // Then find the instructions reachable via the applicable exception handlers.
        while (true) {
            boolean applicableHandlerFound = false;
            for (TryCatchBlockNode tryCatchBlockNode : tryCatchBlocks) {
                // If the handler has already been processed, skip it.
                int handlerIndex = instructions.indexOf(tryCatchBlockNode.handler);
                if (subroutineInsns.get(handlerIndex)) {
                    continue;
                }

                // If an instruction in the exception handler range belongs to the subroutine, the handler
                // can be reached from the routine, and its instructions must be added to the subroutine.
                int startIndex = instructions.indexOf(tryCatchBlockNode.start);
                int endIndex = instructions.indexOf(tryCatchBlockNode.end);
                int firstSubroutineInsnAfterTryCatchStart = subroutineInsns.nextSetBit(startIndex);
                if (firstSubroutineInsnAfterTryCatchStart >= startIndex
                        && firstSubroutineInsnAfterTryCatchStart < endIndex) {
                    findReachableInsns(handlerIndex, subroutineInsns, visitedInsns);
                    applicableHandlerFound = true;
                }
            }
            // If an applicable exception handler has been found, other handlers may become applicable, so
            // we must examine them again.
            if (!applicableHandlerFound) {
                return;
            }
        }
    }

    Finds the instructions that are reachable from the given instruction, without following any JSR
instruction nor any exception handler. For this the control flow graph is visited with a depth
first search.
Params: insnIndex – the index of an instruction of the subroutine.
subroutineInsns – where the indices of the instructions of the subroutine must be stored.
visitedInsns – the indices of the instructions that have been visited so far (including in
    previous calls to this method). This bitset is updated by this method each time a new
    instruction is visited. It is used to make sure each instruction is visited at most once./**
      * Finds the instructions that are reachable from the given instruction, without following any JSR
      * instruction nor any exception handler. For this the control flow graph is visited with a depth
      * first search.
      *
      * @param insnIndex the index of an instruction of the subroutine.
      * @param subroutineInsns where the indices of the instructions of the subroutine must be stored.
      * @param visitedInsns the indices of the instructions that have been visited so far (including in
      *     previous calls to this method). This bitset is updated by this method each time a new
      *     instruction is visited. It is used to make sure each instruction is visited at most once.
      */
    private void findReachableInsns(
            final int insnIndex, final BitSet subroutineInsns, final BitSet visitedInsns) {
        int currentInsnIndex = insnIndex;
        // We implicitly assume below 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).
        while (currentInsnIndex < instructions.size()) {
            // Visit each instruction at most once.
            if (subroutineInsns.get(currentInsnIndex)) {
                return;
            }
            subroutineInsns.set(currentInsnIndex);

            // Check if this instruction has already been visited by another subroutine.
            if (visitedInsns.get(currentInsnIndex)) {
                sharedSubroutineInsns.set(currentInsnIndex);
            }
            visitedInsns.set(currentInsnIndex);

            AbstractInsnNode currentInsnNode = instructions.get(currentInsnIndex);
            if (currentInsnNode.getType() == AbstractInsnNode.JUMP_INSN
                    && currentInsnNode.getOpcode() != JSR) {
                // Don't follow JSR instructions in the control flow graph.
                JumpInsnNode jumpInsnNode = (JumpInsnNode) currentInsnNode;
                findReachableInsns(instructions.indexOf(jumpInsnNode.label), subroutineInsns, visitedInsns);
            } else if (currentInsnNode.getType() == AbstractInsnNode.TABLESWITCH_INSN) {
                TableSwitchInsnNode tableSwitchInsnNode = (TableSwitchInsnNode) currentInsnNode;
                findReachableInsns(
                        instructions.indexOf(tableSwitchInsnNode.dflt), subroutineInsns, visitedInsns);
                for (LabelNode labelNode : tableSwitchInsnNode.labels) {
                    findReachableInsns(instructions.indexOf(labelNode), subroutineInsns, visitedInsns);
                }
            } else if (currentInsnNode.getType() == AbstractInsnNode.LOOKUPSWITCH_INSN) {
                LookupSwitchInsnNode lookupSwitchInsnNode = (LookupSwitchInsnNode) currentInsnNode;
                findReachableInsns(
                        instructions.indexOf(lookupSwitchInsnNode.dflt), subroutineInsns, visitedInsns);
                for (LabelNode labelNode : lookupSwitchInsnNode.labels) {
                    findReachableInsns(instructions.indexOf(labelNode), subroutineInsns, visitedInsns);
                }
            }

            // Check if this instruction falls through to the next instruction; if not, return.
            switch (instructions.get(currentInsnIndex).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 from a parent subroutine.
                    return;
                default:
                    // Go to the next instruction.
                    currentInsnIndex++;
                    break;
            }
        }
    }

    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<>();
        // Create an instantiation of the main "subroutine", which is just the main routine.
        worklist.add(new Instantiation(null, mainSubroutineInsns));

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

    Emits an instantiation of a subroutine, specified by instantiation. May add new
instantiations that are invoked by this one to the worklist, and new try/catch
blocks to newTryCatchBlocks.
Params: instantiation – 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.
newLocalVariables – the local variables list to which the instantiated local variables
    must be appended./**
      * Emits an instantiation of a subroutine, specified by <code>instantiation</code>. May add new
      * instantiations that are invoked by this one to the <code>worklist</code>, and new try/catch
      * blocks to <code>newTryCatchBlocks</code>.
      *
      * @param instantiation 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.
      * @param newLocalVariables the local variables list to which the instantiated local variables
      *     must be appended.
      */
    private void emitInstantiation(
            final Instantiation instantiation,
            final List<Instantiation> worklist,
            final InsnList newInstructions,
            final List<TryCatchBlockNode> newTryCatchBlocks,
            final List<LocalVariableNode> newLocalVariables) {
        LabelNode previousLabelNode = null;
        for (int i = 0; i < instructions.size(); ++i) {
            AbstractInsnNode insnNode = instructions.get(i);
            if (insnNode.getType() == AbstractInsnNode.LABEL) {
                // Always clone all labels, while avoiding to add the same label more than once.
                LabelNode labelNode = (LabelNode) insnNode;
                LabelNode clonedLabelNode = instantiation.getClonedLabel(labelNode);
                if (clonedLabelNode != previousLabelNode) {
                    newInstructions.add(clonedLabelNode);
                    previousLabelNode = clonedLabelNode;
                }
            } else if (instantiation.findOwner(i) == instantiation) {
                // Don't emit instructions that were already emitted by an ancestor subroutine. 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 (insnNode.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 oldest
                    // instantiation that claims to own this instruction.
                    LabelNode retLabel = null;
                    for (Instantiation retLabelOwner = instantiation;
                            retLabelOwner != null;
                            retLabelOwner = retLabelOwner.parent) {
                        if (retLabelOwner.subroutineInsns.get(i)) {
                            retLabel = retLabelOwner.returnLabel;
                        }
                    }
                    if (retLabel == null) {
                        // This is only possible if the mainSubroutine owns a RET instruction, which should
                        // never happen for verifiable code.
                        throw new IllegalArgumentException(
                                "Instruction #" + i + " is a RET not owned by any subroutine");
                    }
                    newInstructions.add(new JumpInsnNode(GOTO, retLabel));
                } else if (insnNode.getOpcode() == JSR) {
                    LabelNode jsrLabelNode = ((JumpInsnNode) insnNode).label;
                    BitSet subroutineInsns = subroutinesInsns.get(jsrLabelNode);
                    Instantiation newInstantiation = new Instantiation(instantiation, subroutineInsns);
                    LabelNode clonedJsrLabelNode = newInstantiation.getClonedLabelForJumpInsn(jsrLabelNode);
                    // Replace the JSR instruction with a GOTO to the instantiated subroutine, and push NULL
                    // for what was once the return address value. This hack allows us to avoid doing any sort
                    // of data flow analysis to figure out which instructions manipulate the old return
                    // address value pointer which is now known to be unneeded.
                    newInstructions.add(new InsnNode(ACONST_NULL));
                    newInstructions.add(new JumpInsnNode(GOTO, clonedJsrLabelNode));
                    newInstructions.add(newInstantiation.returnLabel);
                    // Insert this new instantiation into the queue to be emitted later.
                    worklist.add(newInstantiation);
                } else {
                    newInstructions.add(insnNode.clone(instantiation));
                }
            }
        }

        // Emit the try/catch blocks that are relevant for this instantiation.
        for (TryCatchBlockNode tryCatchBlockNode : tryCatchBlocks) {
            final LabelNode start = instantiation.getClonedLabel(tryCatchBlockNode.start);
            final LabelNode end = instantiation.getClonedLabel(tryCatchBlockNode.end);
            if (start != end) {
                final LabelNode handler =
                        instantiation.getClonedLabelForJumpInsn(tryCatchBlockNode.handler);
                if (start == null || end == null || handler == null) {
                    throw new AssertionError("Internal error!");
                }
                newTryCatchBlocks.add(new TryCatchBlockNode(start, end, handler, tryCatchBlockNode.type));
            }
        }

        // Emit the local variable nodes that are relevant for this instantiation.
        for (LocalVariableNode localVariableNode : localVariables) {
            final LabelNode start = instantiation.getClonedLabel(localVariableNode.start);
            final LabelNode end = instantiation.getClonedLabel(localVariableNode.end);
            if (start != end) {
                newLocalVariables.add(
                        new LocalVariableNode(
                                localVariableNode.name,
                                localVariableNode.desc,
                                localVariableNode.signature,
                                start,
                                end,
                                localVariableNode.index));
            }
        }
    }

    An instantiation of a subroutine. /** An instantiation of a subroutine. */
    private class Instantiation extends AbstractMap<LabelNode, LabelNode> {

        The instantiation from which this one was created (or null for the instantiation of the main "subroutine"). /**
          * The instantiation from which this one was created (or {@literal null} for the instantiation
          * of the main "subroutine").
          */
        final Instantiation parent;

        The original instructions that belong to the subroutine which is instantiated. Bit i is set
iff instruction at index i belongs to this subroutine.
/**
          * The original instructions that belong to the subroutine which is instantiated. Bit i is set
          * iff instruction at index i belongs to this subroutine.
          */
        final BitSet subroutineInsns;

        A map from labels from the original code to labels pointing at code specific to this
instantiation, for use in remapping try/catch blocks, as well as jumps.
Note that in the presence of instructions belonging to several subroutines, we map the
target label of a GOTO to the label used by the oldest instantiation (parent instantiations
are older than their children). This avoids code duplication during inlining in most cases.
/**
          * A map from labels from the original code to labels pointing at code specific to this
          * instantiation, for use in remapping try/catch blocks, as well as jumps.
          *
          * <p>Note that in the presence of instructions belonging to several subroutines, we map the
          * target label of a GOTO to the label used by the oldest instantiation (parent instantiations
          * are older than their children). This avoids code duplication during inlining in most cases.
          */
        final Map<LabelNode, LabelNode> clonedLabels;

        The return label for this instantiation, to which all original returns will be mapped. /** The return label for this instantiation, to which all original returns will be mapped. */
        final LabelNode returnLabel;

        Instantiation(final Instantiation parent, final BitSet subroutineInsns) {
            for (Instantiation instantiation = parent;
                    instantiation != null;
                    instantiation = instantiation.parent) {
                if (instantiation.subroutineInsns == subroutineInsns) {
                    throw new IllegalArgumentException("Recursive invocation of " + subroutineInsns);
                }
            }

            this.parent = parent;
            this.subroutineInsns = subroutineInsns;
            this.returnLabel = parent == null ? null : new LabelNode();
            this.clonedLabels = new HashMap<>();

            // Create a clone of each label in the original code of the subroutine. Note that we collapse
            // labels which point at the same instruction into one.
            LabelNode clonedLabelNode = null;
            for (int insnIndex = 0; insnIndex < instructions.size(); insnIndex++) {
                AbstractInsnNode insnNode = instructions.get(insnIndex);
                if (insnNode.getType() == AbstractInsnNode.LABEL) {
                    LabelNode labelNode = (LabelNode) insnNode;
                    // If we already have a label pointing at this spot, don't recreate it.
                    if (clonedLabelNode == null) {
                        clonedLabelNode = new LabelNode();
                    }
                    clonedLabels.put(labelNode, clonedLabelNode);
                } else if (findOwner(insnIndex) == this) {
                    // We will emit this instruction, so clear the duplicateLabelNode flag since the next
                    // Label will refer to a distinct instruction.
                    clonedLabelNode = null;
                }
            }
        }

        Returns the "owner" of a particular instruction relative to this instantiation: the owner
refers 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
shared instruction, and occurs when multiple subroutines branch to common points of control.
In this case, the owner is the oldest instantiation which owns the instruction in question
(parent instantiations are older than their children).
Params: insnIndex – the index of an 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
          * refers to the Instantiation which will emit the version of this instruction that we will
          * execute.
          *
          * <p>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.
          *
          * <p>Sometimes, however, an instruction can belong to multiple subroutines; this is called a
          * shared instruction, and occurs when multiple subroutines branch to common points of control.
          * In this case, the owner is the oldest instantiation which owns the instruction in question
          * (parent instantiations are older than their children).
          *
          * @param insnIndex the index of an instruction in the original code.
          * @return the "owner" of a particular instruction relative to this instantiation.
          */
        Instantiation findOwner(final int insnIndex) {
            if (!subroutineInsns.get(insnIndex)) {
                return null;
            }
            if (!sharedSubroutineInsns.get(insnIndex)) {
                return this;
            }
            Instantiation owner = this;
            for (Instantiation instantiation = parent;
                    instantiation != null;
                    instantiation = instantiation.parent) {
                if (instantiation.subroutineInsns.get(insnIndex)) {
                    owner = instantiation;
                }
            }
            return owner;
        }

        Returns the clone of the given original label that is appropriate for use in a jump
instruction.
Params: labelNode – a label of the original code.
Returns: a clone of the given label for use in a jump instruction in the inlined code./**
          * Returns the clone of the given original label that is appropriate for use in a jump
          * instruction.
          *
          * @param labelNode a label of the original code.
          * @return a clone of the given label for use in a jump instruction in the inlined code.
          */
        LabelNode getClonedLabelForJumpInsn(final LabelNode labelNode) {
            // findOwner should never return null, because owner is null only if an instruction cannot be
            // reached from this subroutine.
            return findOwner(instructions.indexOf(labelNode)).clonedLabels.get(labelNode);
        }

        Returns the clone of the given original label that is appropriate for use by a try/catch
block or a variable annotation.
Params: labelNode – a label of the original code.
Returns: a clone of the given label for use by a try/catch block or a variable annotation in
    the inlined code./**
          * Returns the clone of the given original label that is appropriate for use by a try/catch
          * block or a variable annotation.
          *
          * @param labelNode a label of the original code.
          * @return a clone of the given label for use by a try/catch block or a variable annotation in
          *     the inlined code.
          */
        LabelNode getClonedLabel(final LabelNode labelNode) {
            return clonedLabels.get(labelNode);
        }

        // AbstractMap implementation

        @Override
        public Set<Map.Entry<LabelNode, LabelNode>> entrySet() {
            throw new UnsupportedOperationException();
        }

        @Override
        public LabelNode get(final Object key) {
            return getClonedLabelForJumpInsn((LabelNode) key);
        }

        @Override
        public boolean equals(final Object other) {
            throw new UnsupportedOperationException();
        }

        @Override
        public int hashCode() {
            throw new UnsupportedOperationException();
        }
    }
}
Params:	methodVisitor – the method visitor to send the resulting inlined method code to, or `null`. access – the method's access flags. name – the method's name. descriptor – the method's descriptor. signature – the method's signature. May be null. exceptions – the internal names of the method's exception classes. May be null.
Throws:	IllegalStateException – if a subclass calls this constructor.
Params:	insnIndex – the index of an instruction in the original code.
Returns:	the "owner" of a particular instruction relative to this instantiation.
Params:	labelNode – a label of the original code.
Returns:	a clone of the given label for use in a jump instruction in the inlined code.
/

java/ 17/ java.base/jdk/internal/org/objectweb/asm/commons/JSRInlinerAdapter.java
