[libFuzzer] new experimental feature: value profiling. Profiles values that affect control flow and treats new values as new coverage.

llvm-svn: 278839

1 files changed, 3 insertions, 2 deletions

diff --git a/llvm/lib/Fuzzer/FuzzerValueBitMap.h b/llvm/lib/Fuzzer/FuzzerValueBitMap.h
index 41169d66bc0..493afc574cc 100644
--- a/llvm/lib/Fuzzer/FuzzerValueBitMap.h
+++ b/llvm/lib/Fuzzer/FuzzerValueBitMap.h
@@ -32,7 +32,7 @@ struct ValueBitMap {
     Map[WordIdx] |= 1UL << BitIdx;
   }
 
-  // Merges 'Other' into 'this', clear Other,
+  // Merges 'Other' into 'this', clears 'Other',
   // returns the number of set bits in 'this'.
   size_t MergeFrom(ValueBitMap &Other) {
     uintptr_t Res = 0;
@@ -43,7 +43,8 @@ struct ValueBitMap {
         Map[i] = (M |= O);
         Other.Map[i] = 0;
       }
-      Res += __builtin_popcountl(M);
+      if (M)
+        Res += __builtin_popcountl(M);
     }
     return Res;
   }