1 //===-- llvm/ADT/Statistic.h - Easy way to expose stats ---------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file defines the 'Statistic' class, which is designed to be an easy way
10 // to expose various metrics from passes.  These statistics are printed at the
11 // end of a run (from llvm_shutdown), when the -stats command line option is
12 // passed on the command line.
13 //
14 // This is useful for reporting information like the number of instructions
15 // simplified, optimized or removed by various transformations, like this:
16 //
17 // static Statistic NumInstsKilled("gcse", "Number of instructions killed");
18 //
19 // Later, in the code: ++NumInstsKilled;
20 //
21 // NOTE: Statistics *must* be declared as global variables.
22 //
23 //===----------------------------------------------------------------------===//
24 
25 #ifndef LLVM_ADT_STATISTIC_H
26 #define LLVM_ADT_STATISTIC_H
27 
28 #include "llvm/Config/llvm-config.h"
29 #include "llvm/Support/Compiler.h"
30 #include <atomic>
31 #include <memory>
32 #include <vector>
33 
34 // Determine whether statistics should be enabled. We must do it here rather
35 // than in CMake because multi-config generators cannot determine this at
36 // configure time.
37 #if !defined(NDEBUG) || LLVM_FORCE_ENABLE_STATS
38 #define LLVM_ENABLE_STATS 1
39 #else
40 #define LLVM_ENABLE_STATS 0
41 #endif
42 
43 namespace llvm {
44 
45 class raw_ostream;
46 class raw_fd_ostream;
47 class StringRef;
48 
49 class StatisticBase {
50 public:
51   const char *DebugType;
52   const char *Name;
53   const char *Desc;
54 
55   StatisticBase(const char *DebugType, const char *Name, const char *Desc)
56       : DebugType(DebugType), Name(Name), Desc(Desc) {}
57 
58   const char *getDebugType() const { return DebugType; }
59   const char *getName() const { return Name; }
60   const char *getDesc() const { return Desc; }
61 };
62 
63 class TrackingStatistic : public StatisticBase {
64 public:
65   std::atomic<unsigned> Value;
66   std::atomic<bool> Initialized;
67 
68   TrackingStatistic(const char *DebugType, const char *Name, const char *Desc)
69       : StatisticBase(DebugType, Name, Desc), Value(0), Initialized(false) {}
70 
71   unsigned getValue() const { return Value.load(std::memory_order_relaxed); }
72 
73   // Allow use of this class as the value itself.
74   operator unsigned() const { return getValue(); }
75 
76   const TrackingStatistic &operator=(unsigned Val) {
77     Value.store(Val, std::memory_order_relaxed);
78     return init();
79   }
80 
81   const TrackingStatistic &operator++() {
82     Value.fetch_add(1, std::memory_order_relaxed);
83     return init();
84   }
85 
86   unsigned operator++(int) {
87     init();
88     return Value.fetch_add(1, std::memory_order_relaxed);
89   }
90 
91   const TrackingStatistic &operator--() {
92     Value.fetch_sub(1, std::memory_order_relaxed);
93     return init();
94   }
95 
96   unsigned operator--(int) {
97     init();
98     return Value.fetch_sub(1, std::memory_order_relaxed);
99   }
100 
101   const TrackingStatistic &operator+=(unsigned V) {
102     if (V == 0)
103       return *this;
104     Value.fetch_add(V, std::memory_order_relaxed);
105     return init();
106   }
107 
108   const TrackingStatistic &operator-=(unsigned V) {
109     if (V == 0)
110       return *this;
111     Value.fetch_sub(V, std::memory_order_relaxed);
112     return init();
113   }
114 
115   void updateMax(unsigned V) {
116     unsigned PrevMax = Value.load(std::memory_order_relaxed);
117     // Keep trying to update max until we succeed or another thread produces
118     // a bigger max than us.
119     while (V > PrevMax && !Value.compare_exchange_weak(
120                               PrevMax, V, std::memory_order_relaxed)) {
121     }
122     init();
123   }
124 
125 protected:
126   TrackingStatistic &init() {
127     if (!Initialized.load(std::memory_order_acquire))
128       RegisterStatistic();
129     return *this;
130   }
131 
132   void RegisterStatistic();
133 };
134 
135 class NoopStatistic : public StatisticBase {
136 public:
137   using StatisticBase::StatisticBase;
138 
139   unsigned getValue() const { return 0; }
140 
141   // Allow use of this class as the value itself.
142   operator unsigned() const { return 0; }
143 
144   const NoopStatistic &operator=(unsigned Val) { return *this; }
145 
146   const NoopStatistic &operator++() { return *this; }
147 
148   unsigned operator++(int) { return 0; }
149 
150   const NoopStatistic &operator--() { return *this; }
151 
152   unsigned operator--(int) { return 0; }
153 
154   const NoopStatistic &operator+=(const unsigned &V) { return *this; }
155 
156   const NoopStatistic &operator-=(const unsigned &V) { return *this; }
157 
158   void updateMax(unsigned V) {}
159 };
160 
161 #if LLVM_ENABLE_STATS
162 using Statistic = TrackingStatistic;
163 #else
164 using Statistic = NoopStatistic;
165 #endif
166 
167 // STATISTIC - A macro to make definition of statistics really simple.  This
168 // automatically passes the DEBUG_TYPE of the file into the statistic.
169 #define STATISTIC(VARNAME, DESC)                                               \
170   static llvm::Statistic VARNAME = {DEBUG_TYPE, #VARNAME, DESC}
171 
172 // ALWAYS_ENABLED_STATISTIC - A macro to define a statistic like STATISTIC but
173 // it is enabled even if LLVM_ENABLE_STATS is off.
174 #define ALWAYS_ENABLED_STATISTIC(VARNAME, DESC)                                \
175   static llvm::TrackingStatistic VARNAME = {DEBUG_TYPE, #VARNAME, DESC}
176 
177 /// Enable the collection and printing of statistics.
178 void EnableStatistics(bool DoPrintOnExit = true);
179 
180 /// Check if statistics are enabled.
181 bool AreStatisticsEnabled();
182 
183 /// Return a file stream to print our output on.
184 std::unique_ptr<raw_fd_ostream> CreateInfoOutputFile();
185 
186 /// Print statistics to the file returned by CreateInfoOutputFile().
187 void PrintStatistics();
188 
189 /// Print statistics to the given output stream.
190 void PrintStatistics(raw_ostream &OS);
191 
192 /// Print statistics in JSON format. This does include all global timers (\see
193 /// Timer, TimerGroup). Note that the timers are cleared after printing and will
194 /// not be printed in human readable form or in a second call of
195 /// PrintStatisticsJSON().
196 void PrintStatisticsJSON(raw_ostream &OS);
197 
198 /// Get the statistics. This can be used to look up the value of
199 /// statistics without needing to parse JSON.
200 ///
201 /// This function does not prevent statistics being updated by other threads
202 /// during it's execution. It will return the value at the point that it is
203 /// read. However, it will prevent new statistics from registering until it
204 /// completes.
205 const std::vector<std::pair<StringRef, unsigned>> GetStatistics();
206 
207 /// Reset the statistics. This can be used to zero and de-register the
208 /// statistics in order to measure a compilation.
209 ///
210 /// When this function begins to call destructors prior to returning, all
211 /// statistics will be zero and unregistered. However, that might not remain the
212 /// case by the time this function finishes returning. Whether update from other
213 /// threads are lost or merely deferred until during the function return is
214 /// timing sensitive.
215 ///
216 /// Callers who intend to use this to measure statistics for a single
217 /// compilation should ensure that no compilations are in progress at the point
218 /// this function is called and that only one compilation executes until calling
219 /// GetStatistics().
220 void ResetStatistics();
221 
222 } // end namespace llvm
223 
224 #endif // LLVM_ADT_STATISTIC_H
225