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+//===-- llvm/ADT/Statistic.h - Easy way to expose stats ---------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the 'Statistic' class, which is designed to be an easy way
+// to expose various metrics from passes.  These statistics are printed at the
+// end of a run (from llvm_shutdown), when the -stats command line option is
+// passed on the command line.
+//
+// This is useful for reporting information like the number of instructions
+// simplified, optimized or removed by various transformations, like this:
+//
+// static Statistic NumInstsKilled("gcse", "Number of instructions killed");
+//
+// Later, in the code: ++NumInstsKilled;
+//
+// NOTE: Statistics *must* be declared as global variables.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_STATISTIC_H
+#define LLVM_ADT_STATISTIC_H
+
+#include "llvm/Config/llvm-config.h"
+#include "llvm/Support/Compiler.h"
+#include <atomic>
+#include <memory>
+#include <vector>
+
+// Determine whether statistics should be enabled. We must do it here rather
+// than in CMake because multi-config generators cannot determine this at
+// configure time.
+#if !defined(NDEBUG) || LLVM_FORCE_ENABLE_STATS
+#define LLVM_ENABLE_STATS 1
+#endif
+
+namespace llvm {
+
+class raw_ostream;
+class raw_fd_ostream;
+class StringRef;
+
+class Statistic {
+public:
+  const char *DebugType;
+  const char *Name;
+  const char *Desc;
+  std::atomic<unsigned> Value;
+  std::atomic<bool> Initialized;
+
+  unsigned getValue() const { return Value.load(std::memory_order_relaxed); }
+  const char *getDebugType() const { return DebugType; }
+  const char *getName() const { return Name; }
+  const char *getDesc() const { return Desc; }
+
+  /// construct - This should only be called for non-global statistics.
+  void construct(const char *debugtype, const char *name, const char *desc) {
+    DebugType = debugtype;
+    Name = name;
+    Desc = desc;
+    Value = 0;
+    Initialized = false;
+  }
+
+  // Allow use of this class as the value itself.
+  operator unsigned() const { return getValue(); }
+
+#if LLVM_ENABLE_STATS
+   const Statistic &operator=(unsigned Val) {
+    Value.store(Val, std::memory_order_relaxed);
+    return init();
+  }
+
+  const Statistic &operator++() {
+    Value.fetch_add(1, std::memory_order_relaxed);
+    return init();
+  }
+
+  unsigned operator++(int) {
+    init();
+    return Value.fetch_add(1, std::memory_order_relaxed);
+  }
+
+  const Statistic &operator--() {
+    Value.fetch_sub(1, std::memory_order_relaxed);
+    return init();
+  }
+
+  unsigned operator--(int) {
+    init();
+    return Value.fetch_sub(1, std::memory_order_relaxed);
+  }
+
+  const Statistic &operator+=(unsigned V) {
+    if (V == 0)
+      return *this;
+    Value.fetch_add(V, std::memory_order_relaxed);
+    return init();
+  }
+
+  const Statistic &operator-=(unsigned V) {
+    if (V == 0)
+      return *this;
+    Value.fetch_sub(V, std::memory_order_relaxed);
+    return init();
+  }
+
+  void updateMax(unsigned V) {
+    unsigned PrevMax = Value.load(std::memory_order_relaxed);
+    // Keep trying to update max until we succeed or another thread produces
+    // a bigger max than us.
+    while (V > PrevMax && !Value.compare_exchange_weak(
+                              PrevMax, V, std::memory_order_relaxed)) {
+    }
+    init();
+  }
+
+#else  // Statistics are disabled in release builds.
+
+  const Statistic &operator=(unsigned Val) {
+    return *this;
+  }
+
+  const Statistic &operator++() {
+    return *this;
+  }
+
+  unsigned operator++(int) {
+    return 0;
+  }
+
+  const Statistic &operator--() {
+    return *this;
+  }
+
+  unsigned operator--(int) {
+    return 0;
+  }
+
+  const Statistic &operator+=(const unsigned &V) {
+    return *this;
+  }
+
+  const Statistic &operator-=(const unsigned &V) {
+    return *this;
+  }
+
+  void updateMax(unsigned V) {}
+
+#endif  // LLVM_ENABLE_STATS
+
+protected:
+  Statistic &init() {
+    if (!Initialized.load(std::memory_order_acquire))
+      RegisterStatistic();
+    return *this;
+  }
+
+  void RegisterStatistic();
+};
+
+// STATISTIC - A macro to make definition of statistics really simple.  This
+// automatically passes the DEBUG_TYPE of the file into the statistic.
+#define STATISTIC(VARNAME, DESC)                                               \
+  static llvm::Statistic VARNAME = {DEBUG_TYPE, #VARNAME, DESC, {0}, {false}}
+
+/// \brief Enable the collection and printing of statistics.
+void EnableStatistics(bool PrintOnExit = true);
+
+/// \brief Check if statistics are enabled.
+bool AreStatisticsEnabled();
+
+/// \brief Return a file stream to print our output on.
+std::unique_ptr<raw_fd_ostream> CreateInfoOutputFile();
+
+/// \brief Print statistics to the file returned by CreateInfoOutputFile().
+void PrintStatistics();
+
+/// \brief Print statistics to the given output stream.
+void PrintStatistics(raw_ostream &OS);
+
+/// Print statistics in JSON format. This does include all global timers (\see
+/// Timer, TimerGroup). Note that the timers are cleared after printing and will
+/// not be printed in human readable form or in a second call of
+/// PrintStatisticsJSON().
+void PrintStatisticsJSON(raw_ostream &OS);
+
+/// \brief Get the statistics. This can be used to look up the value of
+/// statistics without needing to parse JSON.
+///
+/// This function does not prevent statistics being updated by other threads
+/// during it's execution. It will return the value at the point that it is
+/// read. However, it will prevent new statistics from registering until it
+/// completes.
+const std::vector<std::pair<StringRef, unsigned>> GetStatistics();
+
+/// \brief Reset the statistics. This can be used to zero and de-register the
+/// statistics in order to measure a compilation.
+///
+/// When this function begins to call destructors prior to returning, all
+/// statistics will be zero and unregistered. However, that might not remain the
+/// case by the time this function finishes returning. Whether update from other
+/// threads are lost or merely deferred until during the function return is
+/// timing sensitive.
+///
+/// Callers who intend to use this to measure statistics for a single
+/// compilation should ensure that no compilations are in progress at the point
+/// this function is called and that only one compilation executes until calling
+/// GetStatistics().
+void ResetStatistics();
+
+} // end namespace llvm
+
+#endif // LLVM_ADT_STATISTIC_H