Make STATISTIC() values available programmatically

Summary:
It can be useful for tools to be able to retrieve the values of variables
declared via STATISTIC() directly without having to emit them and parse
them back. Use cases include:
* Needing to report specific statistics to a test harness
* Wanting to post-process statistics. For example, to produce a percentage of
  functions that were fully selected by GlobalISel

Make this possible by adding llvm::GetStatistics() which returns an
iterator_range that can be used to inspect the statistics that have been
touched during execution. When statistics are disabled (NDEBUG and not
LLVM_ENABLE_STATISTICS) this method will return an empty range.

This patch doesn't address the effect of multiple compilations within the same
process. In such situations, the statistics will be cumulative for all
compilations up to the GetStatistics() call.

Reviewers: qcolombet, rtereshin, aditya_nandakumar, bogner

Reviewed By: rtereshin, bogner

Subscribers: llvm-commits, mgorny

Differential Revision: https://reviews.llvm.org/D43901

llvm-svn: 326723

1 files changed, 25 insertions, 5 deletions

diff --git a/llvm/lib/Support/Statistic.cpp b/llvm/lib/Support/Statistic.cpp
index 370274dc299..67b07162b9a 100644
--- a/llvm/lib/Support/Statistic.cpp
+++ b/llvm/lib/Support/Statistic.cpp
@@ -52,11 +52,14 @@ static bool Enabled;
 static bool PrintOnExit;
 
 namespace {
-/// StatisticInfo - This class is used in a ManagedStatic so that it is created
-/// on demand (when the first statistic is bumped) and destroyed only when
-/// llvm_shutdown is called.  We print statistics from the destructor.
+/// This class is used in a ManagedStatic so that it is created on demand (when
+/// the first statistic is bumped) and destroyed only when llvm_shutdown is
+/// called. We print statistics from the destructor.
+/// This class is also used to look up statistic values from applications that
+/// use LLVM.
 class StatisticInfo {
   std::vector<const Statistic*> Stats;
+
   friend void llvm::PrintStatistics();
   friend void llvm::PrintStatistics(raw_ostream &OS);
   friend void llvm::PrintStatisticsJSON(raw_ostream &OS);
@@ -64,14 +67,22 @@ class StatisticInfo {
   /// Sort statistics by debugtype,name,description.
   void sort();
 public:
+  using const_iterator = std::vector<const Statistic *>::const_iterator;
+
   StatisticInfo();
   ~StatisticInfo();
 
   void addStatistic(const Statistic *S) {
     Stats.push_back(S);
   }
+
+  const_iterator begin() const { return Stats.begin(); }
+  const_iterator end() const { return Stats.end(); }
+  iterator_range<const_iterator> statistics() const {
+    return {begin(), end()};
+  }
 };
-}
+} // end anonymous namespace
 
 static ManagedStatic<StatisticInfo> StatInfo;
 static ManagedStatic<sys::SmartMutex<true> > StatLock;
@@ -180,7 +191,7 @@ void llvm::PrintStatisticsJSON(raw_ostream &OS) {
 }
 
 void llvm::PrintStatistics() {
-#if !defined(NDEBUG) || defined(LLVM_ENABLE_STATS)
+#if LLVM_ENABLE_STATS
   StatisticInfo &Stats = *StatInfo;
 
   // Statistics not enabled?
@@ -205,3 +216,12 @@ void llvm::PrintStatistics() {
   }
 #endif
 }
+
+const std::vector<std::pair<StringRef, unsigned>> llvm::GetStatistics() {
+  sys::SmartScopedLock<true> Reader(*StatLock);
+  std::vector<std::pair<StringRef, unsigned>> ReturnStats;
+
+  for (const auto &Stat : StatInfo->statistics())
+    ReturnStats.emplace_back(Stat->getName(), Stat->getValue());
+  return ReturnStats;
+}