commit 44e0d16d6262e7825b594787f4844714f5b8008e
author Kostya Serebryany <kcc@google.com> Thu May 09 22:09:25 2019 +0000
committer Copybara-Service <copybara-worker@google.com> Thu Mar 25 23:19:39 2021 -0700
tree bf14c2667232354c213f98c85edc55695c773f1d
parent 3844189011364debef1c4326da9ee91e455a9b8c

[libFuzzer] perform more agressive value profiling in memcmp

llvm-svn: 360385
GitOrigin-RevId: 4a5793f7d07c7fafcc676b431362a01a240b74d3

FuzzerTracePC.cpp

diff --git a/FuzzerTracePC.cpp b/FuzzerTracePC.cpp
index a2d3b7e..4a1308d 100644
--- a/FuzzerTracePC.cpp
+++ b/FuzzerTracePC.cpp
@@ -369,11 +369,16 @@
     Hash ^= (T << 8) | B2[i];
   }
   size_t I = 0;
-  for (; I < Len; I++)
-    if (B1[I] != B2[I] || (StopAtZero && B1[I] == 0))
+  uint8_t HammingDistance = 0;
+  for (; I < Len; I++) {
+    if (B1[I] != B2[I] || (StopAtZero && B1[I] == 0)) {
+      HammingDistance = Popcountll(B1[I] ^ B2[I]);
       break;
+    }
+  }
   size_t PC = reinterpret_cast<size_t>(caller_pc);
   size_t Idx = (PC & 4095) | (I << 12);
+  Idx += HammingDistance;
   ValueProfileMap.AddValue(Idx);
   TORCW.Insert(Idx ^ Hash, Word(B1, Len), Word(B2, Len));
 }