1/*
2 * Copyright (c) 1995, 2003, 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
26package sun.tools.asm;
27
28import sun.tools.java.*;
29import java.io.IOException;
30import java.io.DataOutputStream;
31
32/**
33 * This class is used to assemble the local variable table.
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 * @author Arthur van Hoff
40 */
41final
42class LocalVariableTable {
43    LocalVariable locals[] = new LocalVariable[8];
44    int len;
45
46    /**
47     * Define a new local variable. Merge entries where possible.
48     */
49    void define(MemberDefinition field, int slot, int from, int to) {
50        if (from >= to) {
51            return;
52        }
53        for (int i = 0 ; i < len ; i++) {
54            if ((locals[i].field == field) && (locals[i].slot == slot) &&
55                (from <= locals[i].to) && (to >= locals[i].from)) {
56                locals[i].from = Math.min(locals[i].from, from);
57                locals[i].to = Math.max(locals[i].to, to);
58                return;
59            }
60        }
61        if (len == locals.length) {
62            LocalVariable newlocals[] = new LocalVariable[len * 2];
63            System.arraycopy(locals, 0, newlocals, 0, len);
64            locals = newlocals;
65        }
66        locals[len++] = new LocalVariable(field, slot, from, to);
67    }
68
69    /**
70     * Trim overlapping local ranges.  Java forbids shadowing of
71     * locals in nested scopes, but non-nested scopes may still declare
72     * locals with the same name.  Because local variable ranges are
73     * computed using flow analysis as part of assembly, it isn't
74     * possible to simply make sure variable ranges end where the
75     * enclosing lexical scope ends.  This method makes sure that
76     * variables with the same name don't overlap, giving priority to
77     * fields with higher slot numbers that should have appeared later
78     * in the source.
79     */
80    private void trim_ranges() {
81        for (int i=0; i<len; i++) {
82            for (int j=i+1; j<len; j++) {
83                if ((locals[i].field.getName()==locals[j].field.getName())
84                        && (locals[i].from <= locals[j].to)
85                        && (locals[i].to >= locals[j].from)) {
86                    // At this point we know that both ranges are
87                    // the same name and there is also overlap or they abut
88                    if (locals[i].slot < locals[j].slot) {
89                        if (locals[i].from < locals[j].from) {
90                          locals[i].to = Math.min(locals[i].to, locals[j].from);
91                        } else {
92                          // We've detected two local variables with the
93                          // same name, and the one with the greater slot
94                          // number starts before the other.  This order
95                          // reversal may happen with locals with the same
96                          // name declared in both a try body and an
97                          // associated catch clause.  This is rare, and
98                          // we give up.
99                        }
100                    } else if (locals[i].slot > locals[j].slot) {
101                        if (locals[i].from > locals[j].from) {
102                          locals[j].to = Math.min(locals[j].to, locals[i].from);
103                        } else {
104                          // Same situation as above; just give up.
105                        }
106                    } else {
107                        // This case can happen if there are two variables
108                        // with the same name and slot numbers, and ranges
109                        // that abut.  AFAIK the only way this can occur
110                        // is with multiple static initializers.  Punt.
111                    }
112                }
113            }
114        }
115    }
116
117    /**
118     * Write out the data.
119     */
120    void write(Environment env, DataOutputStream out, ConstantPool tab) throws IOException {
121        trim_ranges();
122        out.writeShort(len);
123        for (int i = 0 ; i < len ; i++) {
124            //System.out.println("pc=" + locals[i].from + ", len=" + (locals[i].to - locals[i].from) + ", nm=" + locals[i].field.getName() + ", slot=" + locals[i].slot);
125            out.writeShort(locals[i].from);
126            out.writeShort(locals[i].to - locals[i].from);
127            out.writeShort(tab.index(locals[i].field.getName().toString()));
128            out.writeShort(tab.index(locals[i].field.getType().getTypeSignature()));
129            out.writeShort(locals[i].slot);
130        }
131    }
132}
133