[libFuzzer] implement print_pcs with trace-pc-guard. Change the trace-pc-guard heuristic for 8-bit counters to look more like in AFL (not that it's provable better, but the existin test preferes this heuristic)

llvm-svn: 281577

1 files changed, 7 insertions, 3 deletions

diff --git a/llvm/lib/Fuzzer/FuzzerValueBitMap.h b/llvm/lib/Fuzzer/FuzzerValueBitMap.h
index 2a917333e21..6f6ca116473 100644
--- a/llvm/lib/Fuzzer/FuzzerValueBitMap.h
+++ b/llvm/lib/Fuzzer/FuzzerValueBitMap.h
@@ -24,12 +24,16 @@ struct ValueBitMap {
   // Clears all bits.
   void Reset() { memset(Map, 0, sizeof(Map)); }
 
-  // Computed a hash function of Value and sets the corresponding bit.
-  inline void AddValue(uintptr_t Value) {
+  // Computes a hash function of Value and sets the corresponding bit.
+  // Returns true if the bit was changed from 0 to 1.
+  inline bool AddValue(uintptr_t Value) {
     uintptr_t Idx = Value < kMapSizeInBits ? Value : Value % kMapSizeInBits;
     uintptr_t WordIdx = Idx / kBitsInWord;
     uintptr_t BitIdx = Idx % kBitsInWord;
-    Map[WordIdx] |= 1UL << BitIdx;
+    uintptr_t Old = Map[WordIdx];
+    uintptr_t New = Old | (1UL << BitIdx);
+    Map[WordIdx] = New;
+    return New != Old;
   }
 
   // Merges 'Other' into 'this', clears 'Other',