1/*
2 * Copyright (C) 2007 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.android.dx.cf.code;
18
19import com.android.dx.rop.type.Type;
20import com.android.dx.rop.type.TypeBearer;
21
22/**
23 * Utility methods to merge various frame information.
24 */
25public final class Merger {
26    /**
27     * Merges two frame types.
28     *
29     * @param ft1 {@code non-null;} a frame type
30     * @param ft2 {@code non-null;} another frame type
31     * @return {@code non-null;} the result of merging the two types
32     */
33    public static TypeBearer mergeType(TypeBearer ft1, TypeBearer ft2) {
34        if ((ft1 == null) || ft1.equals(ft2)) {
35            return ft1;
36        } else if (ft2 == null) {
37            return null;
38        } else {
39            Type type1 = ft1.getType();
40            Type type2 = ft2.getType();
41
42            if (type1 == type2) {
43                return type1;
44            } else if (type1.isReference() && type2.isReference()) {
45                if (type1 == Type.KNOWN_NULL) {
46                    /*
47                     * A known-null merges with any other reference type to
48                     * be that reference type.
49                     */
50                    return type2;
51                } else if (type2 == Type.KNOWN_NULL) {
52                    /*
53                     * The same as above, but this time it's type2 that's
54                     * the known-null.
55                     */
56                    return type1;
57                } else if (type1.isArray() && type2.isArray()) {
58                    TypeBearer componentUnion =
59                        mergeType(type1.getComponentType(),
60                                type2.getComponentType());
61                    if (componentUnion == null) {
62                        /*
63                         * At least one of the types is a primitive type,
64                         * so the merged result is just Object.
65                         */
66                        return Type.OBJECT;
67                    }
68                    return ((Type) componentUnion).getArrayType();
69                } else {
70                    /*
71                     * All other unequal reference types get merged to be
72                     * Object in this phase. This is fine here, but it
73                     * won't be the right thing to do in the verifier.
74                     */
75                    return Type.OBJECT;
76                }
77            } else if (type1.isIntlike() && type2.isIntlike()) {
78                /*
79                 * Merging two non-identical int-like types results in
80                 * the type int.
81                 */
82                return Type.INT;
83            } else {
84                return null;
85            }
86        }
87    }
88}
89