plastic/src/external/java/org/apache/tapestry5/internal/plastic/asm/Edge.java

// ASM: a very small and fast Java bytecode manipulation framework
// Copyright (c) 2000-2011 INRIA, France Telecom
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package org.apache.tapestry5.internal.plastic.asm;

/**
 * An edge in the control flow graph of a method. Each node of this graph is a basic block,
 * represented with the Label corresponding to its first instruction. Each edge goes from one node
 * to another, i.e. from one basic block to another (called the predecessor and successor blocks,
 * respectively). An edge corresponds either to a jump or ret instruction or to an exception
 * handler.
 *
 * @see Label
 * @author Eric Bruneton
 */
final class Edge {

  /**
   * A control flow graph edge corresponding to a jump or ret instruction. Only used with {@link
   * ClassWriter#COMPUTE_FRAMES}.
   */
  static final int JUMP = 0;

  /**
   * A control flow graph edge corresponding to an exception handler. Only used with {@link
   * ClassWriter#COMPUTE_MAXS}.
   */
  static final int EXCEPTION = 0x7FFFFFFF;

  /**
   * Information about this control flow graph edge.
   *
   * <ul>
   *   <li>If {@link ClassWriter#COMPUTE_MAXS} is used, this field contains either a stack size
   *       delta (for an edge corresponding to a jump instruction), or the value EXCEPTION (for an
   *       edge corresponding to an exception handler). The stack size delta is the stack size just
   *       after the jump instruction, minus the stack size at the beginning of the predecessor
   *       basic block, i.e. the one containing the jump instruction.
   *   <li>If {@link ClassWriter#COMPUTE_FRAMES} is used, this field contains either the value JUMP
   *       (for an edge corresponding to a jump instruction), or the index, in the {@link
   *       ClassWriter} type table, of the exception type that is handled (for an edge corresponding
   *       to an exception handler).
   * </ul>
   */
  final int info;

  /** The successor block of this control flow graph edge. */
  final Label successor;

  /**
   * The next edge in the list of outgoing edges of a basic block. See {@link Label#outgoingEdges}.
   */
  Edge nextEdge;

  /**
   * Constructs a new Edge.
   *
   * @param info see {@link #info}.
   * @param successor see {@link #successor}.
   * @param nextEdge see {@link #nextEdge}.
   */
  Edge(final int info, final Label successor, final Edge nextEdge) {
    this.info = info;
    this.successor = successor;
    this.nextEdge = nextEdge;
  }
}