[Timer] Add the timer option -sort-timers to enable/disable report sorting

[Paul-C-Anagnostopoulos]

Summary

This little patch adds the SortByWallClock() function to the TimerGroup class. You can use this function to suppress the usual sorting of the timer reports in wall clock order. I find that order confusing, since the timers move around in the report depending on their percentage of the total wall clock time. Without the sort, the timers appear in the order they were created, which is good for timing sequential phases.

I added one more timer to DAGISelEmitter so I could do a thorough test. The unsorted report looks like:

===-------------------------------------------------------------------------===
                             TableGen Phase Timing
===-------------------------------------------------------------------------===
  Total Execution Time: 128.5448 seconds (128.6254 wall clock)

   ---User Time---   --System Time--   --User+System--   ---Wall Time---  --- Name ---
  15.3505 ( 12.0%)   0.0156 ( 14.3%)  15.3661 ( 12.0%)  15.3869 ( 12.0%)  Parse, build records
  37.8926 ( 29.5%)   0.0468 ( 42.9%)  37.9394 ( 29.5%)  37.9292 ( 29.5%)  Parse patterns
   2.2464 (  1.7%)   0.0000 (  0.0%)   2.2464 (  1.7%)   2.2571 (  1.8%)  Sort patterns
  68.9056 ( 53.6%)   0.0312 ( 28.6%)  68.9368 ( 53.6%)  68.9859 ( 53.6%)  Convert to matchers
   1.0764 (  0.8%)   0.0000 (  0.0%)   1.0764 (  0.8%)   1.0841 (  0.8%)  Optimize matchers
   2.9640 (  2.3%)   0.0156 ( 14.3%)   2.9796 (  2.3%)   2.9772 (  2.3%)  Emit matcher table
   0.0000 (  0.0%)   0.0000 (  0.0%)   0.0000 (  0.0%)   0.0050 (  0.0%)  Write output
  128.4356 (100.0%)   0.1092 (100.0%)  128.5448 (100.0%)  128.6254 (100.0%)  Total

[lattner]

Huh interesting. I'd recommend making this a cl::opt flag so any client of timers can get it. Timer.cpp already has a bunch of these flags (e.g. TrackSpace) so I'd just add one more

[Paul-C-Anagnostopoulos]

I still haven't gotten used to the fact that any old compilation unit can define command line options. Great idea!

[Paul-C-Anagnostopoulos]

I eliminated the new function and replaced it with the new option -sort-timers. Nice!

[Paul-C-Anagnostopoulos]

I will auto-LGTM this on Monday.

[lattner]

LGTM, thanks Paul

llvm/include/llvm/TableGen/Record.h

public:
   }
 
   /// Start timing a phase. Automatically stops any previous phase timer.
   void startTimer(StringRef Name);
 
   /// Stop timing a phase.
   void stopTimer();
 
-  /// Start timing the overall backend. If the backend starts a timer,
+  /// Start timing the overall backend. If the backend itself starts a timer,
   /// then this timer is cleared.
   void startBackendTimer(StringRef Name);
 
   /// Stop timing the overall backend.
   void stopBackendTimer();
 
   /// Stop phase timing and print the report.
   void stopPhaseTiming() {

llvm/lib/Support/Timer.cpp

namespace {
   TrackSpace("track-memory", cl::desc("Enable -time-passes memory "
                                       "tracking (this may be slow)"),
              cl::Hidden);
 
   static cl::opt<std::string, true>
   InfoOutputFilename("info-output-file", cl::value_desc("filename"),
                      cl::desc("File to append -stats and -timer output to"),
                    cl::Hidden, cl::location(getLibSupportInfoOutputFilename()));
+
+  static cl::opt<bool>
+  SortTimers("sort-timers", cl::desc("In the report, sort the timers in each group "
+                                     "in wall clock time order"),
+             cl::init(true), cl::Hidden);
 }
 
 std::unique_ptr<raw_fd_ostream> llvm::CreateInfoOutputFile() {
   const std::string &OutputFilename = getLibSupportInfoOutputFilename();
   if (OutputFilename.empty())
     return std::make_unique<raw_fd_ostream>(2, false); // stderr.
   if (OutputFilename == "-")
     return std::make_unique<raw_fd_ostream>(1, false); // stdout.
void TimerGroup::addTimer(Timer &T) {
   if (FirstTimer)
     FirstTimer->Prev = &T.Next;
   T.Next = FirstTimer;
   T.Prev = &FirstTimer;
   FirstTimer = &T;
 }
 
 void TimerGroup::PrintQueuedTimers(raw_ostream &OS) {
-  // Sort the timers in descending order by amount of time taken.
+  // Perhaps sort the timers in descending order by amount of time taken.
+  if (SortTimers)
     llvm::sort(TimersToPrint);
 
   TimeRecord Total;
   for (const PrintRecord &Record : TimersToPrint)
     Total += Record.Time;
 
   // Print out timing header.
   OS << "===" << std::string(73, '-') << "===\n";
   // Figure out how many spaces to indent TimerGroup name.

llvm/utils/TableGen/DAGISelEmitter.cpp

void DAGISelEmitter::run(raw_ostream &OS) {
 
   Records.startTimer("Emit matcher table");
   EmitMatcherTable(TheMatcher.get(), CGP, OS);
 }
 
 namespace llvm {
 
 void EmitDAGISel(RecordKeeper &RK, raw_ostream &OS) {
+  RK.startTimer("Parse patterns");
   DAGISelEmitter(RK).run(OS);
 }
 
 } // End llvm namespace