js/src/frontend/ForInEmitter.h

   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(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   [[nodiscard]] bool emitIterated();
 109   [[nodiscard]] bool emitInitialize();
 110   [[nodiscard]] bool emitBody();
 111   [[nodiscard]] bool emitEnd(uint32_t forPos);
 112 };
 113
 114 } /* namespace frontend */
 115 } /* namespace js */
 116
 117 #endif /* frontend_ForInEmitter_h */