1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef frontend_CForEmitter_h
#define frontend_CForEmitter_h
#include "mozilla/Attributes.h"
#include "mozilla/Maybe.h"
#include <stddef.h>
#include <stdint.h>
#include "frontend/BytecodeControlStructures.h"
#include "frontend/TDZCheckCache.h"
namespace js {
namespace frontend {
struct BytecodeEmitter;
class EmitterScope;
// Class for emitting bytecode for c-style for block.
//
// Usage: (check for the return value is omitted for simplicity)
//
// `for (init; cond; update) body`
// CForEmitter cfor(this, headLexicalEmitterScopeForLet or nullptr);
// cfor.emitInit(Some(offset_of_init));
// emit(init); // without pushing value
// cfor.emitBody(CForEmitter::Cond::Present, Some(offset_of_body));
// emit(body);
// cfor.emitUpdate(CForEmitter::Update::Present, Some(offset_of_update)));
// emit(update);
// cfor.emitCond(Some(offset_of_for),
// Some(offset_of_cond),
// Some(offset_of_end));
// emit(cond);
// cfor.emitEnd();
//
// `for (;;) body`
// CForEmitter cfor(this, nullptr);
// cfor.emitInit(Nothing());
// cfor.emitBody(CForEmitter::Cond::Missing, Some(offset_of_body));
// emit(body);
// cfor.emitUpdate(CForEmitter::Update::Missing, Nothing());
// cfor.emitCond(Some(offset_of_for),
// Nothing(),
// Some(offset_of_end));
// cfor.emitEnd();
//
class MOZ_STACK_CLASS CForEmitter {
// Basic structure of the bytecode (not complete).
//
// If `cond` is not empty:
// {init}
// JSOP_GOTO entry
// loop:
// {body}
// {update}
// entry:
// {cond}
// JSOP_IFNE loop
//
// If `cond` is empty:
// {init}
// loop:
// {body}
// {update}
// JSOP_GOTO loop
//
public:
enum class Cond { Missing, Present };
enum class Update { Missing, Present };
private:
BytecodeEmitter* bce_;
// The source note index for SRC_FOR.
unsigned noteIndex_ = 0;
// The bytecode offset of loop condition.
// Not the bytecode offset of loop condition expression itself.
ptrdiff_t condOffset_ = 0;
// The base bytecode offset used by SRC_FOR.
ptrdiff_t biasedTop_ = 0;
// Whether the c-style for loop has `cond` and `update`.
Cond cond_ = Cond::Missing;
Update update_ = Update::Missing;
mozilla::Maybe<LoopControl> loopInfo_;
// The lexical scope to be freshened for each iteration.
// See the comment in `emitBody` for more details.
//
// ### Scope freshening
//
// Each iteration of a `for (let V...)` loop creates a fresh loop variable
// binding for V, even if the loop is a C-style `for(;;)` loop:
//
// var funcs = [];
// for (let i = 0; i < 2; i++)
// funcs.push(function() { return i; });
// assertEq(funcs[0](), 0); // the two closures capture...
// assertEq(funcs[1](), 1); // ...two different `i` bindings
//
// This is implemented by "freshening" the implicit block -- changing the
// scope chain to a fresh clone of the instantaneous block object -- each
// iteration, just before evaluating the "update" in for(;;) loops.
//
// ECMAScript doesn't freshen in `for (const ...;;)`. Lack of freshening
// isn't directly observable in-language because `const`s can't be mutated,
// but it *can* be observed in the Debugger API.
const EmitterScope* headLexicalEmitterScopeForLet_;
mozilla::Maybe<TDZCheckCache> tdzCache_;
#ifdef DEBUG
// The state of this emitter.
//
// +-------+ emitInit +------+ emitBody +------+ emitUpdate +--------+
// | Start |--------->| Init |--------->| Body |----------->| Update |-+
// +-------+ +------+ +------+ +--------+ |
// |
// +---------------------------------+
// |
// | emitCond +------+ emitEnd +-----+
// +--------->| Cond |-------->| End |
// +------+ +-----+
enum class State {
// The initial state.
Start,
// After calling emitInit.
Init,
// After calling emitBody.
Body,
// After calling emitUpdate.
Update,
// After calling emitCond.
Cond,
// After calling emitEnd.
End
};
State state_ = State::Start;
#endif
public:
CForEmitter(BytecodeEmitter* bce,
const EmitterScope* headLexicalEmitterScopeForLet);
// Parameters are the offset in the source code for each character below:
//
// for ( x = 10 ; x < 20 ; x ++ ) { f(x); }
// ^ ^ ^ ^ ^ ^
// | | | | | |
// | | | | | endPos
// | | | | |
// | | | | bodyPos
// | | | |
// | | | updatePos
// | | |
// | | condPos
// | |
// | initPos
// |
// forPos
//
// Can be Nothing() if not available.
MOZ_MUST_USE bool emitInit(const mozilla::Maybe<uint32_t>& initPos);
MOZ_MUST_USE bool emitBody(Cond cond,
const mozilla::Maybe<uint32_t>& bodyPos);
MOZ_MUST_USE bool emitUpdate(Update update,
const mozilla::Maybe<uint32_t>& updatePos);
MOZ_MUST_USE bool emitCond(const mozilla::Maybe<uint32_t>& forPos,
const mozilla::Maybe<uint32_t>& condPos,
const mozilla::Maybe<uint32_t>& endPos);
MOZ_MUST_USE bool emitEnd();
};
} /* namespace frontend */
} /* namespace js */
#endif /* frontend_CForEmitter_h */