1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
2  * vim: set ts=8 sts=2 et sw=2 tw=80:
3  * This Source Code Form is subject to the terms of the Mozilla Public
4  * License, v. 2.0. If a copy of the MPL was not distributed with this
5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
6 
7 #ifndef frontend_ForInEmitter_h
8 #define frontend_ForInEmitter_h
9 
10 #include "mozilla/Attributes.h"
11 #include "mozilla/Maybe.h"
12 
13 #include <stdint.h>
14 
15 #include "frontend/BytecodeControlStructures.h"
16 #include "frontend/TDZCheckCache.h"
17 
18 namespace js {
19 namespace frontend {
20 
21 struct BytecodeEmitter;
22 class EmitterScope;
23 
24 // Class for emitting bytecode for for-in loop.
25 //
26 // Usage: (check for the return value is omitted for simplicity)
27 //
28 //   `for (init in iterated) body`
29 //     // headLexicalEmitterScope: lexical scope for init
30 //     ForInEmitter forIn(this, headLexicalEmitterScope);
31 //     forIn.emitIterated();
32 //     emit(iterated);
33 //     forIn.emitInitialize();
34 //     emit(init);
35 //     forIn.emitBody();
36 //     emit(body);
37 //     forIn.emitEnd(Some(offset_of_for));
38 //
39 class MOZ_STACK_CLASS ForInEmitter {
40   BytecodeEmitter* bce_;
41 
42 #ifdef DEBUG
43   // The stack depth before emitting initialize code inside loop.
44   int32_t loopDepth_ = 0;
45 #endif
46 
47   mozilla::Maybe<LoopControl> loopInfo_;
48 
49   // The lexical scope to be freshened for each iteration.  See the comment
50   // in `emitBody` for more details.  Can be nullptr if there's no lexical
51   // scope.
52   const EmitterScope* headLexicalEmitterScope_;
53 
54   // Cache for the iterated value.
55   // (The cache for the iteration body is inside `loopInfo_`)
56   //
57   // The iterated value needs its own TDZCheckCache, separated from both the
58   // enclosing block and the iteration body, in order to make the sanity check
59   // in Ion work properly.
60   // In term of the execution order, the TDZCheckCache for the iterated value
61   // dominates the one for the iteration body, that means the checks in the
62   // iteration body is dead, and we can optimize them away.  But the sanity
63   // check in Ion doesn't know it's dead.
64   // (see bug 1368360 for more context)
65   mozilla::Maybe<TDZCheckCache> tdzCacheForIteratedValue_;
66 
67 #ifdef DEBUG
68   // The state of this emitter.
69   //
70   // +-------+ emitIterated +----------+ emitInitialize +------------+
71   // | Start |------------->| Iterated |--------------->| Initialize |-+
72   // +-------+              +----------+                +------------+ |
73   //                                                                   |
74   //                                +----------------------------------+
75   //                                |
76   //                                | emitBody +------+ emitEnd  +-----+
77   //                                +----------| Body |--------->| End |
78   //                                           +------+          +-----+
79   enum class State {
80     // The initial state.
81     Start,
82 
83     // After calling emitIterated.
84     Iterated,
85 
86     // After calling emitInitialize.
87     Initialize,
88 
89     // After calling emitBody.
90     Body,
91 
92     // After calling emitEnd.
93     End
94   };
95   State state_ = State::Start;
96 #endif
97 
98  public:
99   ForInEmitter(BytecodeEmitter* bce,
100                const EmitterScope* headLexicalEmitterScope);
101 
102   // Parameters are the offset in the source code for each character below:
103   //
104   //   for ( var x in obj ) { ... }
105   //   ^
106   //   |
107   //   forPos
108   //
109   // Can be Nothing() if not available.
110   MOZ_MUST_USE bool emitIterated();
111   MOZ_MUST_USE bool emitInitialize();
112   MOZ_MUST_USE bool emitBody();
113   MOZ_MUST_USE bool emitEnd(const mozilla::Maybe<uint32_t>& forPos);
114 };
115 
116 } /* namespace frontend */
117 } /* namespace js */
118 
119 #endif /* frontend_ForInEmitter_h */
120