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+/* -*- 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_ForInEmitter_h
+#define frontend_ForInEmitter_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/Maybe.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 for-in loop.
+//
+// Usage: (check for the return value is omitted for simplicity)
+//
+// `for (init in iterated) body`
+// // headLexicalEmitterScope: lexical scope for init
+// ForInEmitter forIn(this, headLexicalEmitterScope);
+// forIn.emitIterated();
+// emit(iterated);
+// forIn.emitInitialize();
+// emit(init);
+// forIn.emitBody();
+// emit(body);
+// forIn.emitEnd(offset_of_for);
+//
+class MOZ_STACK_CLASS ForInEmitter {
+ BytecodeEmitter* bce_;
+
+#ifdef DEBUG
+ // The stack depth before emitting initialize code inside loop.
+ int32_t loopDepth_ = 0;
+#endif
+
+ mozilla::Maybe<LoopControl> loopInfo_;
+
+ // The lexical scope to be freshened for each iteration. See the comment
+ // in `emitBody` for more details. Can be nullptr if there's no lexical
+ // scope.
+ const EmitterScope* headLexicalEmitterScope_;
+
+ // Cache for the iterated value.
+ // (The cache for the iteration body is inside `loopInfo_`)
+ //
+ // The iterated value needs its own TDZCheckCache, separated from both the
+ // enclosing block and the iteration body, in order to make the sanity check
+ // in Ion work properly.
+ // In term of the execution order, the TDZCheckCache for the iterated value
+ // dominates the one for the iteration body, that means the checks in the
+ // iteration body is dead, and we can optimize them away. But the sanity
+ // check in Ion doesn't know it's dead.
+ // (see bug 1368360 for more context)
+ mozilla::Maybe<TDZCheckCache> tdzCacheForIteratedValue_;
+
+#ifdef DEBUG
+ // The state of this emitter.
+ //
+ // +-------+ emitIterated +----------+ emitInitialize +------------+
+ // | Start |------------->| Iterated |--------------->| Initialize |-+
+ // +-------+ +----------+ +------------+ |
+ // |
+ // +----------------------------------+
+ // |
+ // | emitBody +------+ emitEnd +-----+
+ // +----------| Body |--------->| End |
+ // +------+ +-----+
+ enum class State {
+ // The initial state.
+ Start,
+
+ // After calling emitIterated.
+ Iterated,
+
+ // After calling emitInitialize.
+ Initialize,
+
+ // After calling emitBody.
+ Body,
+
+ // After calling emitEnd.
+ End
+ };
+ State state_ = State::Start;
+#endif
+
+ public:
+ ForInEmitter(BytecodeEmitter* bce,
+ const EmitterScope* headLexicalEmitterScope);
+
+ // Parameters are the offset in the source code for each character below:
+ //
+ // for ( var x in obj ) { ... }
+ // ^
+ // |
+ // forPos
+ [[nodiscard]] bool emitIterated();
+ [[nodiscard]] bool emitInitialize();
+ [[nodiscard]] bool emitBody();
+ [[nodiscard]] bool emitEnd(uint32_t forPos);
+};
+
+} /* namespace frontend */
+} /* namespace js */
+
+#endif /* frontend_ForInEmitter_h */