diff --git a/llvm/lib/Fuzzer/FuzzerValueBitMap.h b/llvm/lib/Fuzzer/FuzzerValueBitMap.h
new file mode 100644
index 0000000..41169d6
--- /dev/null
+++ b/llvm/lib/Fuzzer/FuzzerValueBitMap.h
@@ -0,0 +1,57 @@
+//===- FuzzerValueBitMap.h - INTERNAL - Bit map -----------------*- C++ -* ===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// ValueBitMap.
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_FUZZER_VALUE_BIT_MAP_H
+#define LLVM_FUZZER_VALUE_BIT_MAP_H
+
+namespace fuzzer {
+
+// A bit map containing kMapSizeInWords bits.
+struct ValueBitMap {
+  static const size_t kMapSizeInBits = 65371;        // Prime.
+  static const size_t kMapSizeInBitsAligned = 65536; // 2^16
+  static const size_t kBitsInWord = (sizeof(uintptr_t) * 8);
+  static const size_t kMapSizeInWords = kMapSizeInBitsAligned / kBitsInWord;
+ public:
+  // Clears all bits.
+  void Reset() { memset(Map, 0, sizeof(Map)); }
+
+  // Computed a hash function of Value and sets the corresponding bit.
+  void AddValue(uintptr_t Value) {
+    uintptr_t Idx = Value % kMapSizeInBits;
+    uintptr_t WordIdx = Idx / kBitsInWord;
+    uintptr_t BitIdx = Idx % kBitsInWord;
+    Map[WordIdx] |= 1UL << BitIdx;
+  }
+
+  // Merges 'Other' into 'this', clear Other,
+  // returns the number of set bits in 'this'.
+  size_t MergeFrom(ValueBitMap &Other) {
+    uintptr_t Res = 0;
+    for (size_t i = 0; i < kMapSizeInWords; i++) {
+      auto O = Other.Map[i];
+      auto M = Map[i];
+      if (O) {
+        Map[i] = (M |= O);
+        Other.Map[i] = 0;
+      }
+      Res += __builtin_popcountl(M);
+    }
+    return Res;
+  }
+
+ private:
+  uintptr_t Map[kMapSizeInWords] __attribute__((aligned(512)));
+};
+
+}  // namespace fuzzer
+
+#endif  // LLVM_FUZZER_VALUE_BIT_MAP_H