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 TrackingStatistic {
50 public:
51   const char *const DebugType;
52   const char *const Name;
53   const char *const Desc;
54 
55   std::atomic<unsigned> Value;
56   std::atomic<bool> Initialized;
57 
58   constexpr TrackingStatistic(const char *DebugType, const char *Name,
59                               const char *Desc)
60       : DebugType(DebugType), Name(Name), Desc(Desc), Value(0),
61         Initialized(false) {}
62 
63   const char *getDebugType() const { return DebugType; }
64   const char *getName() const { return Name; }
65   const char *getDesc() const { return Desc; }
66 
67   unsigned getValue() const { return Value.load(std::memory_order_relaxed); }
68 
69   // Allow use of this class as the value itself.
70   operator unsigned() const { return getValue(); }
71 
72   const TrackingStatistic &operator=(unsigned Val) {
73     Value.store(Val, std::memory_order_relaxed);
74     return init();
75   }
76 
77   const TrackingStatistic &operator++() {
78     Value.fetch_add(1, std::memory_order_relaxed);
79     return init();
80   }
81 
82   unsigned operator++(int) {
83     init();
84     return Value.fetch_add(1, std::memory_order_relaxed);
85   }
86 
87   const TrackingStatistic &operator--() {
88     Value.fetch_sub(1, std::memory_order_relaxed);
89     return init();
90   }
91 
92   unsigned operator--(int) {
93     init();
94     return Value.fetch_sub(1, std::memory_order_relaxed);
95   }
96 
97   const TrackingStatistic &operator+=(unsigned V) {
98     if (V == 0)
99       return *this;
100     Value.fetch_add(V, std::memory_order_relaxed);
101     return init();
102   }
103 
104   const TrackingStatistic &operator-=(unsigned V) {
105     if (V == 0)
106       return *this;
107     Value.fetch_sub(V, std::memory_order_relaxed);
108     return init();
109   }
110 
111   void updateMax(unsigned V) {
112     unsigned PrevMax = Value.load(std::memory_order_relaxed);
113     // Keep trying to update max until we succeed or another thread produces
114     // a bigger max than us.
115     while (V > PrevMax && !Value.compare_exchange_weak(
116                               PrevMax, V, std::memory_order_relaxed)) {
117     }
118     init();
119   }
120 
121 protected:
122   TrackingStatistic &init() {
123     if (!Initialized.load(std::memory_order_acquire))
124       RegisterStatistic();
125     return *this;
126   }
127 
128   void RegisterStatistic();
129 };
130 
131 class NoopStatistic {
132 public:
133   NoopStatistic(const char * /*DebugType*/, const char * /*Name*/,
134                 const char * /*Desc*/) {}
135 
136   unsigned getValue() const { return 0; }
137 
138   // Allow use of this class as the value itself.
139   operator unsigned() const { return 0; }
140 
141   const NoopStatistic &operator=(unsigned Val) { return *this; }
142 
143   const NoopStatistic &operator++() { return *this; }
144 
145   unsigned operator++(int) { return 0; }
146 
147   const NoopStatistic &operator--() { return *this; }
148 
149   unsigned operator--(int) { return 0; }
150 
151   const NoopStatistic &operator+=(const unsigned &V) { return *this; }
152 
153   const NoopStatistic &operator-=(const unsigned &V) { return *this; }
154 
155   void updateMax(unsigned V) {}
156 };
157 
158 #if LLVM_ENABLE_STATS
159 using Statistic = TrackingStatistic;
160 #else
161 using Statistic = NoopStatistic;
162 #endif
163 
164 // STATISTIC - A macro to make definition of statistics really simple.  This
165 // automatically passes the DEBUG_TYPE of the file into the statistic.
166 #define STATISTIC(VARNAME, DESC)                                               \
167   static llvm::Statistic VARNAME = {DEBUG_TYPE, #VARNAME, DESC}
168 
169 // ALWAYS_ENABLED_STATISTIC - A macro to define a statistic like STATISTIC but
170 // it is enabled even if LLVM_ENABLE_STATS is off.
171 #define ALWAYS_ENABLED_STATISTIC(VARNAME, DESC)                                \
172   static llvm::TrackingStatistic VARNAME = {DEBUG_TYPE, #VARNAME, DESC}
173 
174 /// Enable the collection and printing of statistics.
175 void EnableStatistics(bool DoPrintOnExit = true);
176 
177 /// Check if statistics are enabled.
178 bool AreStatisticsEnabled();
179 
180 /// Return a file stream to print our output on.
181 std::unique_ptr<raw_fd_ostream> CreateInfoOutputFile();
182 
183 /// Print statistics to the file returned by CreateInfoOutputFile().
184 void PrintStatistics();
185 
186 /// Print statistics to the given output stream.
187 void PrintStatistics(raw_ostream &OS);
188 
189 /// Print statistics in JSON format. This does include all global timers (\see
190 /// Timer, TimerGroup). Note that the timers are cleared after printing and will
191 /// not be printed in human readable form or in a second call of
192 /// PrintStatisticsJSON().
193 void PrintStatisticsJSON(raw_ostream &OS);
194 
195 /// Get the statistics. This can be used to look up the value of
196 /// statistics without needing to parse JSON.
197 ///
198 /// This function does not prevent statistics being updated by other threads
199 /// during it's execution. It will return the value at the point that it is
200 /// read. However, it will prevent new statistics from registering until it
201 /// completes.
202 const std::vector<std::pair<StringRef, unsigned>> GetStatistics();
203 
204 /// Reset the statistics. This can be used to zero and de-register the
205 /// statistics in order to measure a compilation.
206 ///
207 /// When this function begins to call destructors prior to returning, all
208 /// statistics will be zero and unregistered. However, that might not remain the
209 /// case by the time this function finishes returning. Whether update from other
210 /// threads are lost or merely deferred until during the function return is
211 /// timing sensitive.
212 ///
213 /// Callers who intend to use this to measure statistics for a single
214 /// compilation should ensure that no compilations are in progress at the point
215 /// this function is called and that only one compilation executes until calling
216 /// GetStatistics().
217 void ResetStatistics();
218 
219 } // end namespace llvm
220 
221 #endif // LLVM_ADT_STATISTIC_H
222