[libFuzzer] Implement stat::stability_rate based on the percentage of unstable edges.

Summary:
Created a -print_unstable_stats flag.
When -print_unstable_stats=1, we run it 2 more times on interesting inputs poisoning unstable edges in an array.
On program termination, we run PrintUnstableStats() which will print a line with a stability percentage like AFL does.

Patch by Kyungtak Woo (@kevinwkt).

Reviewers: metzman, Dor1s, kcc, morehouse

Reviewed By: metzman, Dor1s, morehouse

Subscribers: delcypher, llvm-commits, #sanitizers, kcc, morehouse, Dor1s

Differential Revision: https://reviews.llvm.org/D49212

llvm-svn: 337187

1 files changed, 1 insertions, 0 deletions

diff --git a/compiler-rt/lib/fuzzer/FuzzerOptions.h b/compiler-rt/lib/fuzzer/FuzzerOptions.h
index ab90df82a63..e32b7d59b85 100644
--- a/compiler-rt/lib/fuzzer/FuzzerOptions.h
+++ b/compiler-rt/lib/fuzzer/FuzzerOptions.h
@@ -54,6 +54,7 @@ struct FuzzingOptions {
   bool PrintFinalStats = false;
   bool PrintCorpusStats = false;
   bool PrintCoverage = false;
+  bool PrintUnstableStats = false;
   bool DumpCoverage = false;
   bool DetectLeaks = true;
   int PurgeAllocatorIntervalSec = 1;