[Timer][Statistics] Make global constructor ordering more robust

[nhaehnle]

Summary

It was observed in D129117 that the subtle dependency between statistic
and timer code is not entirely robust: the global destructor
~StatisticInfo indirectly calls CreateInfoOutputFile, which requires
the LibSupportInfoOutputFilename to not have been destructed.

By constructing LibSupportInfoOutputFilename before the StatisticInfo
object, the order of destruction is guaranteed.

[efriedma]

LGTM

[MaskRay]

llvm/lib/Support/Timer.cpp

502–503

You can use constructForStatistics while renaming.

llvm/include/llvm/Support/Timer.h

public:
   /// using \c printAll or \c printJSONValues.
   static void clearAll();
 
   const char *printJSONValues(raw_ostream &OS, const char *delim);
 
   /// Prints all timers as JSON key/value pairs.
   static const char *printAllJSONValues(raw_ostream &OS, const char *delim);
 
-  /// Ensure global timer group lists are initialized. This function is mostly
-  /// used by the Statistic code to influence the construction and destruction
-  /// order of the global timer lists.
-  static void ConstructTimerLists();
+  /// Ensure global objects required for statistics printing are initialized.
+  /// This function is used by the Statistic code to ensure correct order of
+  /// global constructors and destructors.
+  static void constructForStatistics();
 
   /// This makes the default group unmanaged, and lets the user manage the
   /// group's lifetime.
   static std::unique_ptr<TimerGroup> aquireDefaultGroup();
 
 private:
   friend class Timer;
   friend void PrintStatisticsJSON(raw_ostream &OS);

llvm/lib/Support/Statistic.cpp

if (EnableStats || Enabled)
       SI.addStatistic(this);
 
     // Remember we have been registered.
     Initialized.store(true, std::memory_order_release);
   }
 }
 
 StatisticInfo::StatisticInfo() {
-  // Ensure timergroup lists are created first so they are destructed after us.
-  TimerGroup::ConstructTimerLists();
+  // Ensure that necessary timer global objects are created first so they are
+  // destructed after us.
+  TimerGroup::constructForStatistics();
 }
 
 // Print information when destroyed, iff command line option is specified.
 StatisticInfo::~StatisticInfo() {
   if (EnableStats || PrintOnExit)
     llvm::PrintStatistics();
 }
 

llvm/lib/Support/Timer.cpp

 
 const char *TimerGroup::printAllJSONValues(raw_ostream &OS, const char *delim) {
   sys::SmartScopedLock<true> L(*TimerLock);
   for (TimerGroup *TG = TimerGroupList; TG; TG = TG->Next)
     delim = TG->printJSONValues(OS, delim);
   return delim;
 }
 
-void TimerGroup::ConstructTimerLists() {
+void TimerGroup::constructForStatistics() {
+  (void)getLibSupportInfoOutputFilename();
   (void)*NamedGroupedTimers;
 }
 
 std::unique_ptr<TimerGroup> TimerGroup::aquireDefaultGroup() {
   return std::unique_ptr<TimerGroup>(DefaultTimerGroup.claim());
 }