Index: lib/Fuzzer/FuzzerDriver.cpp
===================================================================
--- lib/Fuzzer/FuzzerDriver.cpp
+++ lib/Fuzzer/FuzzerDriver.cpp
@@ -355,6 +355,108 @@
   return 0;
 }
 
+int MinimizeDictionary(Fuzzer *F, const std::vector<Unit>& Dict,
+                       UnitVector& Corpus) {
+  std::size_t NumberOfTests = Dict.size() * Corpus.size() * 2;
+  Printf("Started dictionary minimization.");
+  Printf(" Need to perform %zd tests.\n", NumberOfTests);
+
+//  F->Corpus.ResetFeatureSet(); // private method :(
+  F->ResetCoverage();
+  TPC.ResetMaps();
+
+  // Scores for every dictionary unit.
+  std::vector<int> Scores(Dict.size());
+  for (auto &Data : Corpus) {
+    // Get coverage for Corpus unit without modifications.
+    F->RunOne(Data.data(), Data.size());
+    auto InitialCoverage = TPC.GetTotalPCCoverage();
+    std::set<size_t> InitialFeatures;
+    auto InitialResult = TPC.CollectFeatures([&](size_t Feature) -> bool {
+      InitialFeatures.insert(Feature);
+      return true;
+    });
+
+    // DEBUG OUTPUT
+    Printf("Initial corpus unit: ");
+    PrintASCII(Data.data(), Data.size(), "\n");
+    Printf("Initial Result: ");
+    Printf("%zd, Features:", InitialResult);
+    for (size_t F : InitialFeatures)
+      Printf(" %zd", F);
+    Printf(", Coverage: %zd\n", InitialCoverage);
+
+    TPC.ResetMaps();
+    F->ResetCoverage();
+
+    for (std::size_t i = 0; i != Dict.size(); ++i) {
+      auto U = Dict[i];
+      auto Pos = std::search(Data.begin(), Data.end(),
+                             Dict[i].begin(), Dict[i].end());
+      if (Pos == Data.end())
+        continue;
+
+      // DEBUG OUTPUT
+      Printf("\nDictionary unit: ");
+      PrintASCII(Dict[i].data(), Dict[i].size(), "\n");
+
+      // Replace dictionary unit in the data by its masked value.
+      for (auto It = Pos; It != Pos + Dict[i].size(); ++It)
+        *It ^= 0xFF;
+
+      F->RunOne(Data.data(), Data.size());
+      auto ModifiedCoverage = TPC.GetTotalPCCoverage();
+      std::set<size_t> ModifiedFeatures;
+      auto ModifiedResult = TPC.CollectFeatures([&](size_t Feature) -> bool {
+        ModifiedFeatures.insert(Feature);
+        return true;
+      });
+
+      // DEBUG OUTPUT
+      Printf("Initial corpus unit: ");
+      PrintASCII(Data.data(), Data.size(), "\n");
+      Printf("Modified Result: ");
+      Printf("%zd, Features:", ModifiedResult);
+      for (size_t F : ModifiedFeatures)
+        Printf(" %zd", F);
+      Printf(", Coverage: %zd\n", ModifiedCoverage);
+
+      TPC.ResetMaps();
+      F->ResetCoverage();
+
+      // Restore initial contents of the data.
+      for (auto It = Pos; It != Pos + Dict[i].size(); ++It)
+        *It ^= 0xFF;
+
+      // if (InitialCoverage == ModifiedCoverage) {
+      if (InitialFeatures == ModifiedFeatures) {
+        --Scores[i];
+      } else {
+        ++Scores[i];
+      }
+
+      if (i > 20)  // DEBUG for early bailout.
+        break;
+    }
+    Printf("\n"); // DEBUG
+    break; // DEBUG for bailout after the first input.
+  }
+
+  Printf("###### Useless dictionary elements. ######\n");
+  for (std::size_t i = 0; i != Dict.size(); ++i) {
+    // if (Scores[i] > 0)
+    if (Scores[i] == 0)
+       continue;
+
+    // PRINT ALL ELEMENST WITH THEIR SCORES FOR DEBUGING
+    Printf("\"");
+    PrintASCII(Dict[i].data(), Dict[i].size(), "\"");
+    Printf(" # Score: %d\n", Scores[i]);
+  }
+  Printf("###### End of useless dictionary elements. ######\n");
+  return 0;
+}
+
 int FuzzerDriver(int *argc, char ***argv, UserCallback Callback) {
   using namespace fuzzer;
   assert(argc && argv && "Argument pointers cannot be nullptr");
@@ -550,6 +652,19 @@
                            TemporaryMaxLen, /*ExitOnError=*/false);
   }
 
+  if (Flags.minimize_dict) {
+    if (Dictionary.empty() || Inputs->empty()) {
+      Printf("ERROR: can't minimize dict without dict and corpus provided\n");
+      return 1;
+    }
+    if (MinimizeDictionary(F, Dictionary, InitialCorpus)) {
+      Printf("Dictionary minimization failed\n");
+      exit(1);
+    }
+    Printf("Dictionary minimization suceeded\n");
+    exit(0);
+  }
+
   if (Options.MaxLen == 0) {
     size_t MaxLen = 0;
     for (auto &U : InitialCorpus)
Index: lib/Fuzzer/FuzzerFlags.def
===================================================================
--- lib/Fuzzer/FuzzerFlags.def
+++ lib/Fuzzer/FuzzerFlags.def
@@ -39,6 +39,7 @@
   "merged into the 1-st corpus. Only interesting units will be taken. "
   "This flag can be used to minimize a corpus.")
 FUZZER_FLAG_STRING(merge_control_file, "internal flag")
+FUZZER_FLAG_INT(minimize_dict, 0, "internal flag")
 FUZZER_FLAG_INT(minimize_crash, 0, "If 1, minimizes the provided"
   " crash input. Use with -runs=N or -max_total_time=N to limit "
   "the number attempts")