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//===-- llvm/ADT/Statistic.h - Easy way to expose stats ---------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// 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.
#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.
namespace llvm {
class raw_ostream;
class raw_fd_ostream;
class StringRef;
class StatisticBase {
const char *DebugType;
const char *Name;
const char *Desc;
StatisticBase(const char *DebugType, const char *Name, const char *Desc)
: DebugType(DebugType), Name(Name), Desc(Desc) {}
const char *getDebugType() const { return DebugType; }
const char *getName() const { return Name; }
const char *getDesc() const { return Desc; }
class TrackingStatistic : public StatisticBase {
std::atomic<unsigned> Value;
std::atomic<bool> Initialized;
TrackingStatistic(const char *DebugType, const char *Name, const char *Desc)
: StatisticBase(DebugType, Name, Desc), Value(0), Initialized(false) {}
unsigned getValue() const { return Value.load(std::memory_order_relaxed); }
// Allow use of this class as the value itself.
operator unsigned() const { return getValue(); }
const TrackingStatistic &operator=(unsigned Val) {, std::memory_order_relaxed);
return init();
const TrackingStatistic &operator++() {
Value.fetch_add(1, std::memory_order_relaxed);
return init();
unsigned operator++(int) {
return Value.fetch_add(1, std::memory_order_relaxed);
const TrackingStatistic &operator--() {
Value.fetch_sub(1, std::memory_order_relaxed);
return init();
unsigned operator--(int) {
return Value.fetch_sub(1, std::memory_order_relaxed);
const TrackingStatistic &operator+=(unsigned V) {
if (V == 0)
return *this;
Value.fetch_add(V, std::memory_order_relaxed);
return init();
const TrackingStatistic &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)) {
TrackingStatistic &init() {
if (!Initialized.load(std::memory_order_acquire))
return *this;
void RegisterStatistic();
class NoopStatistic : public StatisticBase {
using StatisticBase::StatisticBase;
unsigned getValue() const { return 0; }
// Allow use of this class as the value itself.
operator unsigned() const { return 0; }
const NoopStatistic &operator=(unsigned Val) { return *this; }
const NoopStatistic &operator++() { return *this; }
unsigned operator++(int) { return 0; }
const NoopStatistic &operator--() { return *this; }
unsigned operator--(int) { return 0; }
const NoopStatistic &operator+=(const unsigned &V) { return *this; }
const NoopStatistic &operator-=(const unsigned &V) { return *this; }
void updateMax(unsigned V) {}
using Statistic = TrackingStatistic;
using Statistic = NoopStatistic;
// STATISTIC - A macro to make definition of statistics really simple. This
// automatically passes the DEBUG_TYPE of the file into the statistic.
static llvm::Statistic VARNAME = {DEBUG_TYPE, #VARNAME, DESC}
// ALWAYS_ENABLED_STATISTIC - A macro to define a statistic like STATISTIC but
// it is enabled even if LLVM_ENABLE_STATS is off.
static llvm::TrackingStatistic VARNAME = {DEBUG_TYPE, #VARNAME, DESC}
/// Enable the collection and printing of statistics.
void EnableStatistics(bool PrintOnExit = true);
/// Check if statistics are enabled.
bool AreStatisticsEnabled();
/// Return a file stream to print our output on.
std::unique_ptr<raw_fd_ostream> CreateInfoOutputFile();
/// Print statistics to the file returned by CreateInfoOutputFile().
void PrintStatistics();
/// 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);
/// 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();
/// 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