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diff --git a/js/src/perf/jsperf.h b/js/src/perf/jsperf.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* 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 perf_jsperf_h
+#define perf_jsperf_h
+
+#include "jstypes.h"
+
+#include "js/TypeDecls.h"
+#include "js/Utility.h"
+
+namespace JS {
+
+/*
+ * JS::PerfMeasurement is a generic way to access detailed performance
+ * measurement APIs provided by your operating system.  The details of
+ * exactly how this works and what can be measured are highly
+ * system-specific, but this interface is (one hopes) implementable
+ * on top of all of them.
+ *
+ * To use this API, create a PerfMeasurement object, passing its
+ * constructor a bitmask indicating which events you are interested
+ * in.  Thereafter, Start() zeroes all counters and starts timing;
+ * Stop() stops timing again; and the counters for the events you
+ * requested are available as data values after calling Stop().  The
+ * object may be reused for many measurements.
+ */
+class JS_FRIEND_API(PerfMeasurement)
+{
+  protected:
+    // Implementation-specific data, if any.
+    void* impl;
+
+  public:
+    /*
+     * Events that may be measured.  Taken directly from the list of
+     * "generalized hardware performance event types" in the Linux
+     * perf_event API, plus some of the "software events".
+     */
+    enum EventMask {
+        CPU_CYCLES          = 0x00000001,
+        INSTRUCTIONS        = 0x00000002,
+        CACHE_REFERENCES    = 0x00000004,
+        CACHE_MISSES        = 0x00000008,
+        BRANCH_INSTRUCTIONS = 0x00000010,
+        BRANCH_MISSES       = 0x00000020,
+        BUS_CYCLES          = 0x00000040,
+        PAGE_FAULTS         = 0x00000080,
+        MAJOR_PAGE_FAULTS   = 0x00000100,
+        CONTEXT_SWITCHES    = 0x00000200,
+        CPU_MIGRATIONS      = 0x00000400,
+
+        ALL                 = 0x000007ff,
+        NUM_MEASURABLE_EVENTS  = 11
+    };
+
+    /*
+     * Bitmask of events that will be measured when this object is
+     * active (between Start() and Stop()).  This may differ from the
+     * bitmask passed to the constructor if the platform does not
+     * support measuring all of the requested events.
+     */
+    const EventMask eventsMeasured;
+
+    /*
+     * Counters for each measurable event.
+     * Immediately after one of these objects is created, all of the
+     * counters for enabled events will be zero, and all of the
+     * counters for disabled events will be uint64_t(-1).
+     */
+    uint64_t cpu_cycles;
+    uint64_t instructions;
+    uint64_t cache_references;
+    uint64_t cache_misses;
+    uint64_t branch_instructions;
+    uint64_t branch_misses;
+    uint64_t bus_cycles;
+    uint64_t page_faults;
+    uint64_t major_page_faults;
+    uint64_t context_switches;
+    uint64_t cpu_migrations;
+
+    /*
+     * Prepare to measure the indicated set of events.  If not all of
+     * the requested events can be measured on the current platform,
+     * then the eventsMeasured bitmask will only include the subset of
+     * |toMeasure| corresponding to the events that can be measured.
+     */
+    explicit PerfMeasurement(EventMask toMeasure);
+
+    /* Done with this set of measurements, tear down OS-level state. */
+    ~PerfMeasurement();
+
+    /* Start a measurement cycle. */
+    void start();
+
+    /*
+     * End a measurement cycle, and for each enabled counter, add the
+     * number of measured events of that type to the appropriate
+     * visible variable.
+     */
+    void stop();
+
+    /* Reset all enabled counters to zero. */
+    void reset();
+
+    /*
+     * True if this platform supports measuring _something_, i.e. it's
+     * not using the stub implementation.
+     */
+    static bool canMeasureSomething();
+};
+
+/* Inject a Javascript wrapper around the above C++ class into the
+ * Javascript object passed as an argument (this will normally be a
+ * global object).  The JS-visible API is identical to the C++ API.
+ */
+extern JS_FRIEND_API(JSObject*)
+    RegisterPerfMeasurement(JSContext* cx, JS::HandleObject global);
+
+/*
+ * Given a Value which contains an instance of the aforementioned
+ * wrapper class, extract the C++ object.  Returns nullptr if the
+ * Value is not an instance of the wrapper.
+ */
+extern JS_FRIEND_API(PerfMeasurement*)
+    ExtractPerfMeasurement(const Value& wrapper);
+
+} // namespace JS
+
+#endif /* perf_jsperf_h */