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diff --git a/js/src/jit/AtomicOp.h b/js/src/jit/AtomicOp.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 jit_AtomicOp_h
+#define jit_AtomicOp_h
+
+namespace js {
+namespace jit {
+
+// Types of atomic operation, shared by MIR and LIR.
+
+enum AtomicOp {
+  AtomicFetchAddOp,
+  AtomicFetchSubOp,
+  AtomicFetchAndOp,
+  AtomicFetchOrOp,
+  AtomicFetchXorOp
+};
+
+// Memory barrier types, shared by MIR and LIR.
+//
+// MembarSynchronizing is here because some platforms can make the
+// distinction (DSB vs DMB on ARM, SYNC vs parameterized SYNC on MIPS)
+// but there's been no reason to use it yet.
+
+enum MemoryBarrierBits {
+  MembarLoadLoad = 1,
+  MembarLoadStore = 2,
+  MembarStoreStore = 4,
+  MembarStoreLoad = 8,
+
+  MembarSynchronizing = 16,
+
+  // For validity testing
+  MembarNobits = 0,
+  MembarAllbits = 31,
+};
+
+static inline constexpr MemoryBarrierBits operator|(MemoryBarrierBits a,
+                                                    MemoryBarrierBits b) {
+  return MemoryBarrierBits(int(a) | int(b));
+}
+
+static inline constexpr MemoryBarrierBits operator&(MemoryBarrierBits a,
+                                                    MemoryBarrierBits b) {
+  return MemoryBarrierBits(int(a) & int(b));
+}
+
+static inline constexpr MemoryBarrierBits operator~(MemoryBarrierBits a) {
+  return MemoryBarrierBits(~int(a));
+}
+
+// Standard barrier bits for a full barrier.
+static constexpr MemoryBarrierBits MembarFull =
+    MembarLoadLoad | MembarLoadStore | MembarStoreLoad | MembarStoreStore;
+
+// Standard sets of barrier bits for atomic loads and stores.
+// See http://gee.cs.oswego.edu/dl/jmm/cookbook.html for more.
+static constexpr MemoryBarrierBits MembarBeforeLoad = MembarNobits;
+static constexpr MemoryBarrierBits MembarAfterLoad =
+    MembarLoadLoad | MembarLoadStore;
+static constexpr MemoryBarrierBits MembarBeforeStore = MembarStoreStore;
+static constexpr MemoryBarrierBits MembarAfterStore = MembarStoreLoad;
+
+struct Synchronization {
+  const MemoryBarrierBits barrierBefore;
+  const MemoryBarrierBits barrierAfter;
+
+  constexpr Synchronization(MemoryBarrierBits before, MemoryBarrierBits after)
+      : barrierBefore(before), barrierAfter(after) {}
+
+  static Synchronization None() {
+    return Synchronization(MemoryBarrierBits(MembarNobits),
+                           MemoryBarrierBits(MembarNobits));
+  }
+
+  static Synchronization Full() {
+    return Synchronization(MembarFull, MembarFull);
+  }
+
+  static Synchronization Load() {
+    return Synchronization(MembarBeforeLoad, MembarAfterLoad);
+  }
+
+  static Synchronization Store() {
+    return Synchronization(MembarBeforeStore, MembarAfterStore);
+  }
+
+  bool isNone() const { return (barrierBefore | barrierAfter) == MembarNobits; }
+};
+
+}  // namespace jit
+}  // namespace js
+
+#endif /* jit_AtomicOp_h */