1/*
2 * Copyright (C) 2013 Apple Inc. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 *    notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 *    notice, this list of conditions and the following disclaimer in the
11 *    documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
14 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
16 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
17 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
18 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
19 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
20 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
21 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
23 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#ifndef DFGBinarySwitch_h
27#define DFGBinarySwitch_h
28
29#if ENABLE(DFG_JIT)
30
31#include "GPRInfo.h"
32#include "MacroAssembler.h"
33
34namespace JSC { namespace DFG {
35
36// The BinarySwitch class makes it easy to emit a switch statement over either
37// 32-bit integers or pointers, where the switch uses a tree of branches
38// rather than a jump table. This makes it particularly useful if the case
39// values are too far apart to make a jump table practical, or if there are
40// sufficiently few cases that the total cost of log(numCases) branches is
41// less than the cost of an indirected jump.
42//
43// In an effort to simplify the logic of emitting code for each case, this
44// uses an iterator style, rather than a functor callback style. This makes
45// sense because even the iterator implementation found herein is relatively
46// simple, whereas the code it's used from is usually quite complex - one
47// example being the trie-of-trees string switch implementation, where the
48// code emitted for each case involves recursing to emit code for a sub-trie.
49//
50// Use this like so:
51//
52// BinarySwitch switch(valueReg, casesVector, BinarySwitch::Int32);
53// while (switch.advance(jit)) {
54//     int value = switch.caseValue();
55//     unsigned index = switch.caseIndex(); // index into casesVector, above
56//     ... // generate code for this case
57// }
58// switch.fallThrough().link(&jit);
59
60class BinarySwitch {
61public:
62    enum Type {
63        Int32,
64        IntPtr
65    };
66
67    BinarySwitch(GPRReg value, const Vector<int64_t>& cases, Type);
68
69    unsigned caseIndex() const { return m_cases[m_caseIndex].index; }
70    int64_t caseValue() const { return m_cases[m_caseIndex].value; }
71
72    bool advance(MacroAssembler&);
73
74    MacroAssembler::JumpList& fallThrough() { return m_fallThrough; }
75
76private:
77    void build(unsigned start, unsigned end);
78
79    GPRReg m_value;
80
81    struct Case {
82        Case() { }
83
84        Case(int64_t value, unsigned index)
85            : value(value)
86            , index(index)
87        {
88        }
89
90        bool operator<(const Case& other) const
91        {
92            return value < other.value;
93        }
94
95        int64_t value;
96        unsigned index;
97    };
98
99    Vector<Case> m_cases;
100
101    enum BranchKind {
102        NotEqualToFallThrough,
103        NotEqualToPush,
104        LessThanToPush,
105        Pop,
106        ExecuteCase
107    };
108
109    struct BranchCode {
110        BranchCode() { }
111
112        BranchCode(BranchKind kind, unsigned index = UINT_MAX)
113            : kind(kind)
114            , index(index)
115        {
116        }
117
118        BranchKind kind;
119        unsigned index;
120    };
121
122    Vector<BranchCode> m_branches;
123
124    unsigned m_index;
125    unsigned m_caseIndex;
126    Vector<MacroAssembler::Jump> m_jumpStack;
127
128    MacroAssembler::JumpList m_fallThrough;
129
130    unsigned m_medianBias;
131
132    Type m_type;
133};
134
135} } // namespace JSC::DFG
136
137#endif // ENABLE(DFG_JIT)
138
139#endif // DFGBinarySwitch_h
140
141