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diff --git a/js/src/frontend/WhileEmitter.h b/js/src/frontend/WhileEmitter.h
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+++ b/js/src/frontend/WhileEmitter.h
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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_WhileEmitter_h
+#define frontend_WhileEmitter_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 for emitting bytecode for while loop.
+//
+// Usage: (check for the return value is omitted for simplicity)
+//
+//   `while (cond) body`
+//     WhileEmitter wh(this);
+//     wh.emitCond(Some(offset_of_while),
+//                 Some(offset_of_body),
+//                 Some(offset_of_end));
+//     emit(cond);
+//     wh.emitBody();
+//     emit(body);
+//     wh.emitEnd();
+//
+class MOZ_STACK_CLASS WhileEmitter {
+  BytecodeEmitter* bce_;
+
+  mozilla::Maybe<LoopControl> loopInfo_;
+
+  // Cache for the loop body, which is enclosed by the cache in `loopInfo_`,
+  // which is effectively for the loop condition.
+  mozilla::Maybe<TDZCheckCache> tdzCacheForBody_;
+
+#ifdef DEBUG
+  // The state of this emitter.
+  //
+  // +-------+ emitCond +------+ emitBody +------+ emitEnd  +-----+
+  // | Start |--------->| Cond |--------->| Body |--------->| End |
+  // +-------+          +------+          +------+          +-----+
+  enum class State {
+    // The initial state.
+    Start,
+
+    // After calling emitCond.
+    Cond,
+
+    // After calling emitBody.
+    Body,
+
+    // After calling emitEnd.
+    End
+  };
+  State state_ = State::Start;
+#endif
+
+ public:
+  explicit WhileEmitter(BytecodeEmitter* bce);
+
+  // Parameters are the offset in the source code for each character below:
+  //
+  //   while ( x < 20 ) { ... }
+  //   ^       ^              ^
+  //   |       |              |
+  //   |       |              endPos_
+  //   |       |
+  //   |       condPos_
+  //   |
+  //   whilePos_
+  //
+  // Can be Nothing() if not available.
+  MOZ_MUST_USE bool emitCond(const mozilla::Maybe<uint32_t>& whilePos,
+                             const mozilla::Maybe<uint32_t>& condPos,
+                             const mozilla::Maybe<uint32_t>& endPos);
+  MOZ_MUST_USE bool emitBody();
+  MOZ_MUST_USE bool emitEnd();
+};
+
+} /* namespace frontend */
+} /* namespace js */
+
+#endif /* frontend_WhileEmitter_h */