1 files changed, 66 insertions, 0 deletions
diff --git a/js/src/gc/RelocationOverlay.h b/js/src/gc/RelocationOverlay.h
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+++ b/js/src/gc/RelocationOverlay.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/. */
+
+/*
+ * GC-internal definition of relocation overlay used while moving cells.
+ */
+
+#ifndef gc_RelocationOverlay_h
+#define gc_RelocationOverlay_h
+
+#include "mozilla/Assertions.h"
+
+#include <stdint.h>
+
+#include "gc/Cell.h"
+
+namespace js {
+namespace gc {
+
+/*
+ * This structure overlays a Cell that has been moved and provides a way to find
+ * its new location. It's used during generational and compacting GC.
+ */
+class RelocationOverlay : public Cell {
+ public:
+  /* The location the cell has been moved to, stored in the cell header. */
+  Cell* forwardingAddress() const {
+    MOZ_ASSERT(isForwarded());
+    return reinterpret_cast<Cell*>(header_ & ~RESERVED_MASK);
+  }
+
+ protected:
+  /* A list entry to track all relocated things. */
+  RelocationOverlay* next_;
+
+  explicit RelocationOverlay(Cell* dst);
+
+ public:
+  static const RelocationOverlay* fromCell(const Cell* cell) {
+    return static_cast<const RelocationOverlay*>(cell);
+  }
+
+  static RelocationOverlay* fromCell(Cell* cell) {
+    return static_cast<RelocationOverlay*>(cell);
+  }
+
+  static RelocationOverlay* forwardCell(Cell* src, Cell* dst);
+
+  RelocationOverlay*& nextRef() {
+    MOZ_ASSERT(isForwarded());
+    return next_;
+  }
+
+  RelocationOverlay* next() const {
+    MOZ_ASSERT(isForwarded());
+    return next_;
+  }
+};
+
+}  // namespace gc
+}  // namespace js
+
+#endif /* gc_RelocationOverlay_h */