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diff --git a/js/src/jit/SafepointIndex.h b/js/src/jit/SafepointIndex.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_SafepointIndex_h
+#define jit_SafepointIndex_h
+
+#include "mozilla/Assertions.h"
+
+#include <stdint.h>
+
+#include "jit/IonTypes.h"
+
+namespace js {
+namespace jit {
+
+class LSafepoint;
+class CodegenSafepointIndex;
+
+// Two-tuple that lets you look up the safepoint entry given the
+// displacement of a call instruction within the JIT code.
+class SafepointIndex {
+  // The displacement is the distance from the first byte of the JIT'd code
+  // to the return address (of the call that the safepoint was generated for).
+  uint32_t displacement_ = 0;
+
+  // Offset within the safepoint buffer.
+  uint32_t safepointOffset_ = 0;
+
+ public:
+  inline explicit SafepointIndex(const CodegenSafepointIndex& csi);
+
+  uint32_t displacement() const { return displacement_; }
+  uint32_t safepointOffset() const { return safepointOffset_; }
+};
+
+class CodegenSafepointIndex {
+  uint32_t displacement_ = 0;
+
+  LSafepoint* safepoint_ = nullptr;
+
+ public:
+  CodegenSafepointIndex(uint32_t displacement, LSafepoint* safepoint)
+      : displacement_(displacement), safepoint_(safepoint) {}
+
+  LSafepoint* safepoint() const { return safepoint_; }
+  uint32_t displacement() const { return displacement_; }
+  void adjustDisplacement(uint32_t offset) {
+    MOZ_ASSERT(offset >= displacement_);
+    displacement_ = offset;
+  }
+  inline SnapshotOffset snapshotOffset() const;
+  inline bool hasSnapshotOffset() const;
+};
+
+// The OSI point is patched to a call instruction. Therefore, the
+// returnPoint for an OSI call is the address immediately following that
+// call instruction. The displacement of that point within the assembly
+// buffer is the |returnPointDisplacement|.
+class OsiIndex {
+  uint32_t callPointDisplacement_;
+  uint32_t snapshotOffset_;
+
+ public:
+  OsiIndex(uint32_t callPointDisplacement, uint32_t snapshotOffset)
+      : callPointDisplacement_(callPointDisplacement),
+        snapshotOffset_(snapshotOffset) {}
+
+  uint32_t returnPointDisplacement() const;
+  uint32_t callPointDisplacement() const { return callPointDisplacement_; }
+  uint32_t snapshotOffset() const { return snapshotOffset_; }
+};
+
+} /* namespace jit */
+} /* namespace js */
+
+#endif /* jit_SafepointIndex_h */