1 //===-- Statistic.cpp - Easy way to expose stats information --------------===//
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 implements the 'Statistic' class, which is designed to be an easy
10 // way to expose various success metrics from passes.  These statistics are
11 // printed at the end of a run, when the -stats command line option is enabled
12 // 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 NumInstEliminated("GCSE", "Number of instructions killed");
18 //
19 // Later, in the code: ++NumInstEliminated;
20 //
21 //===----------------------------------------------------------------------===//
22 
23 #include "llvm/ADT/Statistic.h"
24 #include "llvm/ADT/StringExtras.h"
25 #include "llvm/Support/CommandLine.h"
26 #include "llvm/Support/Compiler.h"
27 #include "llvm/Support/Debug.h"
28 #include "llvm/Support/Format.h"
29 #include "llvm/Support/ManagedStatic.h"
30 #include "llvm/Support/Mutex.h"
31 #include "llvm/Support/Timer.h"
32 #include "llvm/Support/YAMLTraits.h"
33 #include "llvm/Support/raw_ostream.h"
34 #include <algorithm>
35 #include <cstring>
36 using namespace llvm;
37 
38 /// -stats - Command line option to cause transformations to emit stats about
39 /// what they did.
40 ///
41 static cl::opt<bool> Stats(
42     "stats",
43     cl::desc("Enable statistics output from program (available with Asserts)"),
44     cl::Hidden);
45 
46 static cl::opt<bool> StatsAsJSON("stats-json",
47                                  cl::desc("Display statistics as json data"),
48                                  cl::Hidden);
49 
50 static bool Enabled;
51 static bool PrintOnExit;
52 
53 namespace {
54 /// This class is used in a ManagedStatic so that it is created on demand (when
55 /// the first statistic is bumped) and destroyed only when llvm_shutdown is
56 /// called. We print statistics from the destructor.
57 /// This class is also used to look up statistic values from applications that
58 /// use LLVM.
59 class StatisticInfo {
60   std::vector<Statistic*> Stats;
61 
62   friend void llvm::PrintStatistics();
63   friend void llvm::PrintStatistics(raw_ostream &OS);
64   friend void llvm::PrintStatisticsJSON(raw_ostream &OS);
65 
66   /// Sort statistics by debugtype,name,description.
67   void sort();
68 public:
69   using const_iterator = std::vector<Statistic *>::const_iterator;
70 
71   StatisticInfo();
72   ~StatisticInfo();
73 
74   void addStatistic(Statistic *S) {
75     Stats.push_back(S);
76   }
77 
78   const_iterator begin() const { return Stats.begin(); }
79   const_iterator end() const { return Stats.end(); }
80   iterator_range<const_iterator> statistics() const {
81     return {begin(), end()};
82   }
83 
84   void reset();
85 };
86 } // end anonymous namespace
87 
88 static ManagedStatic<StatisticInfo> StatInfo;
89 static ManagedStatic<sys::SmartMutex<true> > StatLock;
90 
91 /// RegisterStatistic - The first time a statistic is bumped, this method is
92 /// called.
93 void Statistic::RegisterStatistic() {
94   // If stats are enabled, inform StatInfo that this statistic should be
95   // printed.
96   // llvm_shutdown calls destructors while holding the ManagedStatic mutex.
97   // These destructors end up calling PrintStatistics, which takes StatLock.
98   // Since dereferencing StatInfo and StatLock can require taking the
99   // ManagedStatic mutex, doing so with StatLock held would lead to a lock
100   // order inversion. To avoid that, we dereference the ManagedStatics first,
101   // and only take StatLock afterwards.
102   if (!Initialized.load(std::memory_order_relaxed)) {
103     sys::SmartMutex<true> &Lock = *StatLock;
104     StatisticInfo &SI = *StatInfo;
105     sys::SmartScopedLock<true> Writer(Lock);
106     // Check Initialized again after acquiring the lock.
107     if (Initialized.load(std::memory_order_relaxed))
108       return;
109     if (Stats || Enabled)
110       SI.addStatistic(this);
111 
112     // Remember we have been registered.
113     Initialized.store(true, std::memory_order_release);
114   }
115 }
116 
117 StatisticInfo::StatisticInfo() {
118   // Ensure timergroup lists are created first so they are destructed after us.
119   TimerGroup::ConstructTimerLists();
120 }
121 
122 // Print information when destroyed, iff command line option is specified.
123 StatisticInfo::~StatisticInfo() {
124   if (::Stats || PrintOnExit)
125     llvm::PrintStatistics();
126 }
127 
128 void llvm::EnableStatistics(bool PrintOnExit) {
129   Enabled = true;
130   ::PrintOnExit = PrintOnExit;
131 }
132 
133 bool llvm::AreStatisticsEnabled() {
134   return Enabled || Stats;
135 }
136 
137 void StatisticInfo::sort() {
138   std::stable_sort(Stats.begin(), Stats.end(),
139                    [](const Statistic *LHS, const Statistic *RHS) {
140     if (int Cmp = std::strcmp(LHS->getDebugType(), RHS->getDebugType()))
141       return Cmp < 0;
142 
143     if (int Cmp = std::strcmp(LHS->getName(), RHS->getName()))
144       return Cmp < 0;
145 
146     return std::strcmp(LHS->getDesc(), RHS->getDesc()) < 0;
147   });
148 }
149 
150 void StatisticInfo::reset() {
151   sys::SmartScopedLock<true> Writer(*StatLock);
152 
153   // Tell each statistic that it isn't registered so it has to register
154   // again. We're holding the lock so it won't be able to do so until we're
155   // finished. Once we've forced it to re-register (after we return), then zero
156   // the value.
157   for (auto *Stat : Stats) {
158     // Value updates to a statistic that complete before this statement in the
159     // iteration for that statistic will be lost as intended.
160     Stat->Initialized = false;
161     Stat->Value = 0;
162   }
163 
164   // Clear the registration list and release the lock once we're done. Any
165   // pending updates from other threads will safely take effect after we return.
166   // That might not be what the user wants if they're measuring a compilation
167   // but it's their responsibility to prevent concurrent compilations to make
168   // a single compilation measurable.
169   Stats.clear();
170 }
171 
172 void llvm::PrintStatistics(raw_ostream &OS) {
173   StatisticInfo &Stats = *StatInfo;
174 
175   // Figure out how long the biggest Value and Name fields are.
176   unsigned MaxDebugTypeLen = 0, MaxValLen = 0;
177   for (size_t i = 0, e = Stats.Stats.size(); i != e; ++i) {
178     MaxValLen = std::max(MaxValLen,
179                          (unsigned)utostr(Stats.Stats[i]->getValue()).size());
180     MaxDebugTypeLen = std::max(MaxDebugTypeLen,
181                          (unsigned)std::strlen(Stats.Stats[i]->getDebugType()));
182   }
183 
184   Stats.sort();
185 
186   // Print out the statistics header...
187   OS << "===" << std::string(73, '-') << "===\n"
188      << "                          ... Statistics Collected ...\n"
189      << "===" << std::string(73, '-') << "===\n\n";
190 
191   // Print all of the statistics.
192   for (size_t i = 0, e = Stats.Stats.size(); i != e; ++i)
193     OS << format("%*u %-*s - %s\n",
194                  MaxValLen, Stats.Stats[i]->getValue(),
195                  MaxDebugTypeLen, Stats.Stats[i]->getDebugType(),
196                  Stats.Stats[i]->getDesc());
197 
198   OS << '\n';  // Flush the output stream.
199   OS.flush();
200 }
201 
202 void llvm::PrintStatisticsJSON(raw_ostream &OS) {
203   sys::SmartScopedLock<true> Reader(*StatLock);
204   StatisticInfo &Stats = *StatInfo;
205 
206   Stats.sort();
207 
208   // Print all of the statistics.
209   OS << "{\n";
210   const char *delim = "";
211   for (const Statistic *Stat : Stats.Stats) {
212     OS << delim;
213     assert(yaml::needsQuotes(Stat->getDebugType()) == yaml::QuotingType::None &&
214            "Statistic group/type name is simple.");
215     assert(yaml::needsQuotes(Stat->getName()) == yaml::QuotingType::None &&
216            "Statistic name is simple");
217     OS << "\t\"" << Stat->getDebugType() << '.' << Stat->getName() << "\": "
218        << Stat->getValue();
219     delim = ",\n";
220   }
221   // Print timers.
222   TimerGroup::printAllJSONValues(OS, delim);
223 
224   OS << "\n}\n";
225   OS.flush();
226 }
227 
228 void llvm::PrintStatistics() {
229 #if LLVM_ENABLE_STATS
230   sys::SmartScopedLock<true> Reader(*StatLock);
231   StatisticInfo &Stats = *StatInfo;
232 
233   // Statistics not enabled?
234   if (Stats.Stats.empty()) return;
235 
236   // Get the stream to write to.
237   std::unique_ptr<raw_ostream> OutStream = CreateInfoOutputFile();
238   if (StatsAsJSON)
239     PrintStatisticsJSON(*OutStream);
240   else
241     PrintStatistics(*OutStream);
242 
243 #else
244   // Check if the -stats option is set instead of checking
245   // !Stats.Stats.empty().  In release builds, Statistics operators
246   // do nothing, so stats are never Registered.
247   if (Stats) {
248     // Get the stream to write to.
249     std::unique_ptr<raw_ostream> OutStream = CreateInfoOutputFile();
250     (*OutStream) << "Statistics are disabled.  "
251                  << "Build with asserts or with -DLLVM_ENABLE_STATS\n";
252   }
253 #endif
254 }
255 
256 const std::vector<std::pair<StringRef, unsigned>> llvm::GetStatistics() {
257   sys::SmartScopedLock<true> Reader(*StatLock);
258   std::vector<std::pair<StringRef, unsigned>> ReturnStats;
259 
260   for (const auto &Stat : StatInfo->statistics())
261     ReturnStats.emplace_back(Stat->getName(), Stat->getValue());
262   return ReturnStats;
263 }
264 
265 void llvm::ResetStatistics() {
266   StatInfo->reset();
267 }
268