diff --git a/compiler-rt/lib/fuzzer/FuzzerDriver.cpp b/compiler-rt/lib/fuzzer/FuzzerDriver.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerDriver.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerDriver.cpp
@@ -755,6 +755,8 @@
     Options.FeaturesDir = Flags.features_dir;
     ValidateDirectoryExists(Options.FeaturesDir, Flags.create_missing_dirs);
   }
+  if (Flags.mutation_graph_file)
+    Options.MutationGraphFile = Flags.mutation_graph_file;
   if (Flags.collect_data_flow)
     Options.CollectDataFlow = Flags.collect_data_flow;
   if (Flags.stop_file)
diff --git a/compiler-rt/lib/fuzzer/FuzzerFlags.def b/compiler-rt/lib/fuzzer/FuzzerFlags.def
--- a/compiler-rt/lib/fuzzer/FuzzerFlags.def
+++ b/compiler-rt/lib/fuzzer/FuzzerFlags.def
@@ -88,6 +88,11 @@
   "Every time a new input is added to the corpus, a corresponding file in the features_dir"
   " is created containing the unique features of that input."
   " Features are stored in binary format.")
+FUZZER_FLAG_STRING(mutation_graph_file, "internal flag. Saves a graph (in DOT"
+  " format) to mutation_graph_file. The graph contains a vertex for each input"
+  " that has unique coverage; directed edges are provided between parents and"
+  " children where the child has unique coverage, and are recorded with the"
+  " type of mutation that caused the child.")
 FUZZER_FLAG_INT(use_counters, 1, "Use coverage counters")
 FUZZER_FLAG_INT(use_memmem, 1,
                 "Use hints from intercepting memmem, strstr, etc")
diff --git a/compiler-rt/lib/fuzzer/FuzzerIO.h b/compiler-rt/lib/fuzzer/FuzzerIO.h
--- a/compiler-rt/lib/fuzzer/FuzzerIO.h
+++ b/compiler-rt/lib/fuzzer/FuzzerIO.h
@@ -29,6 +29,9 @@
 void WriteToFile(const std::string &Data, const std::string &Path);
 void WriteToFile(const Unit &U, const std::string &Path);
 
+void AppendToFile(const uint8_t *Data, size_t Size, const std::string &Path);
+void AppendToFile(const std::string &Data, const std::string &Path);
+
 void ReadDirToVectorOfUnits(const char *Path, Vector<Unit> *V,
                             long *Epoch, size_t MaxSize, bool ExitOnError);
 
diff --git a/compiler-rt/lib/fuzzer/FuzzerIO.cpp b/compiler-rt/lib/fuzzer/FuzzerIO.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerIO.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerIO.cpp
@@ -77,6 +77,19 @@
   fclose(Out);
 }
 
+void AppendToFile(const std::string &Data, const std::string &Path) {
+  AppendToFile(reinterpret_cast<const uint8_t *>(Data.c_str()), Data.size(),
+               Path);
+}
+
+void AppendToFile(const uint8_t *Data, size_t Size, const std::string &Path) {
+  FILE *Out = fopen(Path.c_str(), "a");
+  if (!Out)
+    return;
+  fwrite(Data, sizeof(Data[0]), Size, Out);
+  fclose(Out);
+}
+
 void ReadDirToVectorOfUnits(const char *Path, Vector<Unit> *V,
                             long *Epoch, size_t MaxSize, bool ExitOnError) {
   long E = Epoch ? *Epoch : 0;
diff --git a/compiler-rt/lib/fuzzer/FuzzerLoop.cpp b/compiler-rt/lib/fuzzer/FuzzerLoop.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerLoop.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerLoop.cpp
@@ -463,6 +463,37 @@
              DirPlusFile(FeaturesDir, NewFile));
 }
 
+static void WriteEdgeToMutationGraphFile(const std::string &MutationGraphFile,
+                                         const InputInfo *II,
+                                         const InputInfo *BaseII,
+                                         const std::string &MS) {
+  if (MutationGraphFile.empty())
+    return;
+
+  std::string Sha1 = Sha1ToString(II->Sha1);
+
+  std::string OutputString;
+
+  // Add a new vertex.
+  OutputString.append("\"");
+  OutputString.append(Sha1);
+  OutputString.append("\"\n");
+
+  // Add a new edge if there is base input.
+  if (BaseII) {
+    std::string BaseSha1 = Sha1ToString(BaseII->Sha1);
+    OutputString.append("\"");
+    OutputString.append(BaseSha1);
+    OutputString.append("\" -> \"");
+    OutputString.append(Sha1);
+    OutputString.append("\" [label=\"");
+    OutputString.append(MS);
+    OutputString.append("\"];\n");
+  }
+
+  AppendToFile(OutputString, MutationGraphFile);
+}
+
 bool Fuzzer::RunOne(const uint8_t *Data, size_t Size, bool MayDeleteFile,
                     InputInfo *II, bool ForceAddToCorpus,
                     bool *FoundUniqFeatures) {
@@ -497,6 +528,8 @@
                            TimeOfUnit, UniqFeatureSetTmp, DFT, II);
     WriteFeatureSetToFile(Options.FeaturesDir, Sha1ToString(NewII->Sha1),
                           NewII->UniqFeatureSet);
+    WriteEdgeToMutationGraphFile(Options.MutationGraphFile, NewII, II,
+                                 MD.MutationSequence());
     return true;
   }
   if (II && FoundUniqFeaturesOfII &&
diff --git a/compiler-rt/lib/fuzzer/FuzzerMutate.h b/compiler-rt/lib/fuzzer/FuzzerMutate.h
--- a/compiler-rt/lib/fuzzer/FuzzerMutate.h
+++ b/compiler-rt/lib/fuzzer/FuzzerMutate.h
@@ -26,6 +26,8 @@
   void StartMutationSequence();
   /// Print the current sequence of mutations.
   void PrintMutationSequence();
+  /// Return the current sequence of mutations.
+  std::string MutationSequence();
   /// Indicate that the current sequence of mutations was successful.
   void RecordSuccessfulMutationSequence();
   /// Mutates data by invoking user-provided mutator.
diff --git a/compiler-rt/lib/fuzzer/FuzzerMutate.cpp b/compiler-rt/lib/fuzzer/FuzzerMutate.cpp
--- a/compiler-rt/lib/fuzzer/FuzzerMutate.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerMutate.cpp
@@ -494,6 +494,15 @@
   }
 }
 
+std::string MutationDispatcher::MutationSequence() {
+  std::string MS;
+  for (auto M : CurrentMutatorSequence) {
+    MS += M.Name;
+    MS += "-";
+  }
+  return MS;
+}
+
 size_t MutationDispatcher::Mutate(uint8_t *Data, size_t Size, size_t MaxSize) {
   return MutateImpl(Data, Size, MaxSize, Mutators);
 }
diff --git a/compiler-rt/lib/fuzzer/FuzzerOptions.h b/compiler-rt/lib/fuzzer/FuzzerOptions.h
--- a/compiler-rt/lib/fuzzer/FuzzerOptions.h
+++ b/compiler-rt/lib/fuzzer/FuzzerOptions.h
@@ -59,6 +59,7 @@
   std::string DataFlowTrace;
   std::string CollectDataFlow;
   std::string FeaturesDir;
+  std::string MutationGraphFile;
   std::string StopFile;
   bool SaveArtifacts = true;
   bool PrintNEW = true; // Print a status line when new units are found;
diff --git a/compiler-rt/test/fuzzer/mutation-graph.test b/compiler-rt/test/fuzzer/mutation-graph.test
new file mode 100644
--- /dev/null
+++ b/compiler-rt/test/fuzzer/mutation-graph.test
@@ -0,0 +1,17 @@
+REQUIRES: linux, x86_64
+RUN: %cpp_compiler %S/SimpleTest.cpp -o %t-SimpleTest
+
+RUN: rm -rf %t-SimpleTestGraph
+
+RUN: not %run %t-SimpleTest -seed=1 -max_len=3 -mutation_graph_file=%t-SimpleTestGraph 2>&1 | FileCheck %s
+CHECK: BINGO
+
+RUN: cat %t-SimpleTestGraph | FileCheck %s --check-prefix=GRAPH
+
+# A vertex and edge that correspond to the discovery of "H"
+GRAPH: "7cf184f4c67ad58283ecb19349720b0cae756829"
+GRAPH: {{.*}} -> "7cf184f4c67ad58283ecb19349720b0cae756829" [label="{{.*}}"];
+
+# A vertex and edge that correspond to the discovery of "Hi"
+GRAPH: "94dd9e08c129c785f7f256e82fbe0a30e6d1ae40"
+GRAPH: {{.*}} -> "94dd9e08c129c785f7f256e82fbe0a30e6d1ae40" [label="{{.*}}"];