1 files changed, 18 insertions, 1 deletions
diff --git a/compiler-rt/lib/fuzzer/FuzzerMutate.h b/compiler-rt/lib/fuzzer/FuzzerMutate.h
index 828ecc13d86..d89667cc41c 100644
--- a/compiler-rt/lib/fuzzer/FuzzerMutate.h
+++ b/compiler-rt/lib/fuzzer/FuzzerMutate.h
@@ -93,9 +93,22 @@ public:
 
   Random &GetRand() { return Rand; }
 
+  /// Records tally of mutations resulting in new coverage, for usefulness
+  /// metric.
+  void RecordUsefulMutations();
+
+  /// Outputs usefulness stats on command line if option is enabled.
   void PrintMutationStats();
 
-  void RecordUsefulMutations();
+  /// Recalculates mutation stats based on latest run data.
+  void UpdateMutationStats();
+
+  /// Sets weights based on mutation performance during fuzzer run.
+  void UpdateDistribution();
+
+  /// Returns the index of a mutation based on how useful it has been.
+  /// Favors mutations with higher usefulness ratios but can return any index.
+  size_t WeightedIndex();
 
  private:
   struct Mutator {
@@ -156,6 +169,10 @@ public:
 
   Vector<Mutator> Mutators;
   Vector<Mutator> DefaultMutators;
+
+  // Used to weight mutations based on usefulness.
+  Vector<double> Stats;
+  std::discrete_distribution<size_t> Distribution;
 };
 
 }  // namespace fuzzer