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1   /*
2    * Copyright (c) 1994, 2004, Oracle and/or its affiliates. All rights reserved.
3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4    *
5    * This code is free software; you can redistribute it and/or modify it
6    * under the terms of the GNU General Public License version 2 only, as
7    * published by the Free Software Foundation.  Oracle designates this
8    * particular file as subject to the "Classpath" exception as provided
9    * by Oracle in the LICENSE file that accompanied this code.
10   *
11   * This code is distributed in the hope that it will be useful, but WITHOUT
12   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14   * version 2 for more details (a copy is included in the LICENSE file that
15   * accompanied this code).
16   *
17   * You should have received a copy of the GNU General Public License version
18   * 2 along with this work; if not, write to the Free Software Foundation,
19   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20   *
21   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22   * or visit www.oracle.com if you need additional information or have any
23   * questions.
24   */
25  
26  package sun.tools.asm;
27  
28  import sun.tools.java.MemberDefinition;
29  import java.io.OutputStream;
30  
31  /**
32   * A label instruction. This is a 0 size instruction.
33   * It is the only valid target of a branch instruction.
34   *
35   * WARNING: The contents of this source file are not part of any
36   * supported API.  Code that depends on them does so at its own risk:
37   * they are subject to change or removal without notice.
38   */
39  public final
40  class Label extends Instruction {
41      static int labelCount = 0;
42      int ID;
43      int depth;
44      MemberDefinition locals[];
45  
46      /**
47       * Constructor
48       */
49      public Label() {
50          super(0, opc_label, null);
51          this.ID = ++labelCount;
52      }
53  
54      /**
55       * Get the final destination, eliminate jumps gotos, and jumps to
56       * labels that are immediately folowed by another label. The depth
57       * field is used to leave bread crumbs to avoid infinite loops.
58       */
59      Label getDestination() {
60          Label lbl = this;
61          if ((next != null) && (next != this) && (depth == 0)) {
62              depth = 1;
63  
64              switch (next.opc) {
65                case opc_label:
66                  lbl = ((Label)next).getDestination();
67                  break;
68  
69                case opc_goto:
70                  lbl = ((Label)next.value).getDestination();
71                  break;
72  
73                case opc_ldc:
74                case opc_ldc_w:
75                  if (next.value instanceof Integer) {
76                      Instruction inst = next.next;
77                      if (inst.opc == opc_label) {
78                          inst = ((Label)inst).getDestination().next;
79                      }
80  
81                      if (inst.opc == opc_ifeq) {
82                          if (((Integer)next.value).intValue() == 0) {
83                              lbl = (Label)inst.value;
84                          } else {
85                              lbl = new Label();
86                              lbl.next = inst.next;
87                              inst.next = lbl;
88                          }
89                          lbl = lbl.getDestination();
90                          break;
91                      }
92                      if (inst.opc == opc_ifne) {
93                          if (((Integer)next.value).intValue() == 0) {
94                              lbl = new Label();
95                              lbl.next = inst.next;
96                              inst.next = lbl;
97                          } else {
98                              lbl = (Label)inst.value;
99                          }
100                         lbl = lbl.getDestination();
101                         break;
102                     }
103                 }
104                 break;
105             }
106             depth = 0;
107         }
108         return lbl;
109     }
110 
111     public String toString() {
112         String s = "$" + ID + ":";
113         if (value != null)
114             s = s + " stack=" + value;
115         return s;
116     }
117 }