1/*
2 * Copyright (C) 2013, 2015 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#pragma once
27
28#if ENABLE(JIT)
29
30#include "GPRInfo.h"
31#include "MacroAssembler.h"
32#include <wtf/WeakRandom.h>
33
34namespace JSC {
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// ... = jit.jump(); // you have to jump out yourself; falling through causes undefined behavior
58// }
59// switch.fallThrough().link(&jit);
60
61class BinarySwitch {
62public:
63 enum Type {
64 Int32,
65 IntPtr
66 };
67
68 BinarySwitch(GPRReg value, const Vector<int64_t>& cases, Type);
69 ~BinarySwitch();
70
71 unsigned caseIndex() const { return m_cases[m_caseIndex].index; }
72 int64_t caseValue() const { return m_cases[m_caseIndex].value; }
73
74 bool advance(MacroAssembler&);
75
76 MacroAssembler::JumpList& fallThrough() { return m_fallThrough; }
77
78private:
79 void build(unsigned start, bool hardStart, unsigned end);
80
81 Type m_type;
82 GPRReg m_value;
83
84 struct Case {
85 Case() { }
86
87 Case(int64_t value, unsigned index)
88 : value(value)
89 , index(index)
90 {
91 }
92
93 bool operator<(const Case& other) const
94 {
95 return value < other.value;
96 }
97
98 void dump(PrintStream& out) const;
99
100 int64_t value;
101 unsigned index;
102 };
103
104 Vector<Case> m_cases;
105
106 enum BranchKind {
107 NotEqualToFallThrough,
108 NotEqualToPush,
109 LessThanToPush,
110 Pop,
111 ExecuteCase
112 };
113
114 struct BranchCode {
115 BranchCode() { }
116
117 BranchCode(BranchKind kind, unsigned index = UINT_MAX)
118 : kind(kind)
119 , index(index)
120 {
121 }
122
123 void dump(PrintStream& out) const;
124
125 BranchKind kind;
126 unsigned index;
127 };
128
129 WeakRandom m_weakRandom;
130
131 Vector<BranchCode> m_branches;
132
133 unsigned m_index;
134 unsigned m_caseIndex;
135 Vector<MacroAssembler::Jump> m_jumpStack;
136
137 MacroAssembler::JumpList m_fallThrough;
138};
139
140} // namespace JSC
141
142#endif // ENABLE(JIT)
143