js/src/frontend/ForOfLoopControl.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_ForOfLoopControl_h
   8 #define frontend_ForOfLoopControl_h
   9
  10 #include "mozilla/Maybe.h"  // mozilla::Maybe
  11
  12 #include <stdint.h>  // int32_t, uint32_t
  13
  14 #include "frontend/BytecodeControlStructures.h"  // NestableControl, LoopControl
  15 #include "frontend/IteratorKind.h"               // IteratorKind
  16 #include "frontend/SelfHostedIter.h"             // SelfHostedIter
  17 #include "frontend/TryEmitter.h"                 // TryEmitter
  18 #include "vm/CompletionKind.h"                   // CompletionKind
  19
  20 namespace js {
  21 namespace frontend {
  22
  23 struct BytecodeEmitter;
  24 class BytecodeOffset;
  25 class EmitterScope;
  26
  27 class ForOfLoopControl : public LoopControl {
  28   // The stack depth of the iterator.
  29   int32_t iterDepth_;
  30
  31   // For-of loops, when throwing from non-iterator code (i.e. from the body
  32   // or from evaluating the LHS of the loop condition), need to call
  33   // IteratorClose.  This is done by enclosing the body of the loop with
  34   // try-catch and calling IteratorClose in the `catch` block.
  35   //
  36   // If IteratorClose itself throws, we must not re-call
  37   // IteratorClose. Since non-local jumps like break and return call
  38   // IteratorClose, whenever a non-local jump is emitted, we must
  39   // prevent the catch block from catching any exception thrown from
  40   // IteratorClose. We do this by wrapping the non-local jump in a
  41   // ForOfIterClose try-note.
  42   //
  43   //   for (x of y) {
  44   //     // Operations for iterator (IteratorNext etc) are outside of
  45   //     // try-block.
  46   //     try {
  47   //       ...
  48   //       if (...) {
  49   //         // Before non-local jump, close iterator.
  50   //         CloseIter(iter, CompletionKind::Return); // Covered by
  51   //         return;                                  // trynote
  52   //       }
  53   //       ...
  54   //     } catch (e) {
  55   //       // When propagating an exception, we swallow any exceptions
  56   //       // thrown while closing the iterator.
  57   //       CloseIter(iter, CompletionKind::Throw);
  58   //       throw e;
  59   //     }
  60   //   }
  61   mozilla::Maybe<TryEmitter> tryCatch_;
  62
  63   // Used to track if any yields were emitted between calls to to
  64   // emitBeginCodeNeedingIteratorClose and emitEndCodeNeedingIteratorClose.
  65   uint32_t numYieldsAtBeginCodeNeedingIterClose_;
  66
  67   SelfHostedIter selfHostedIter_;
  68
  69   IteratorKind iterKind_;
  70
  71  public:
  72   ForOfLoopControl(BytecodeEmitter* bce, int32_t iterDepth,
  73                    SelfHostedIter selfHostedIter, IteratorKind iterKind);
  74
  75   [[nodiscard]] bool emitBeginCodeNeedingIteratorClose(BytecodeEmitter* bce);
  76   [[nodiscard]] bool emitEndCodeNeedingIteratorClose(BytecodeEmitter* bce);
  77
  78   [[nodiscard]] bool emitIteratorCloseInInnermostScopeWithTryNote(
  79       BytecodeEmitter* bce,
  80       CompletionKind completionKind = CompletionKind::Normal);
  81   [[nodiscard]] bool emitIteratorCloseInScope(
  82       BytecodeEmitter* bce, EmitterScope& currentScope,
  83       CompletionKind completionKind = CompletionKind::Normal);
  84
  85   [[nodiscard]] bool emitPrepareForNonLocalJumpFromScope(
  86       BytecodeEmitter* bce, EmitterScope& currentScope, bool isTarget,
  87       BytecodeOffset* tryNoteStart);
  88 };
  89 template <>
  90 inline bool NestableControl::is<ForOfLoopControl>() const {
  91   return kind_ == StatementKind::ForOfLoop;
  92 }
  93
  94 } /* namespace frontend */
  95 } /* namespace js */
  96
  97 #endif /* frontend_ForOfLoopControl_h */