Index: llvm/include/llvm/Support/GraphWriter.h
===================================================================
--- llvm/include/llvm/Support/GraphWriter.h
+++ llvm/include/llvm/Support/GraphWriter.h
@@ -330,11 +330,8 @@
                        const Twine &Title = "",
                        std::string Filename = "") {
   int FD;
-  // Windows can't always handle long paths, so limit the length of the name.
-  std::string N = Name.str();
-  N = N.substr(0, std::min<std::size_t>(N.size(), 140));
   if (Filename.empty()) {
-    Filename = createGraphFilename(N, FD);
+    Filename = createGraphFilename(Name.str(), FD);
   } else {
     std::error_code EC = sys::fs::openFileForWrite(Filename, FD);
 
Index: llvm/lib/Support/GraphWriter.cpp
===================================================================
--- llvm/lib/Support/GraphWriter.cpp
+++ llvm/lib/Support/GraphWriter.cpp
@@ -76,10 +76,35 @@
   return Colors[ColorNumber % NumColors];
 }
 
+static std::string replaceIllegalFilenameChars(std::string Filename,
+                                               const char ReplacementChar) {
+#ifdef _WIN32
+  std::string IllegalChars = "\\/:?\"<>|";
+#else
+  std::string IllegalChars = "/";
+#endif
+
+  for (std::string::iterator It = IllegalChars.begin(); It < IllegalChars.end();
+       ++It) {
+    std::replace(Filename.begin(), Filename.end(), *It, ReplacementChar);
+  }
+
+  return Filename;
+}
+
 std::string llvm::createGraphFilename(const Twine &Name, int &FD) {
   FD = -1;
   SmallString<128> Filename;
-  std::error_code EC = sys::fs::createTemporaryFile(Name, "dot", FD, Filename);
+
+  // Windows can't always handle long paths, so limit the length of the name.
+  std::string N = Name.str();
+  N = N.substr(0, std::min<std::size_t>(N.size(), 140));
+
+  // Replace illegal characters in graph Filename with '_' if needed
+  std::string CleansedName = replaceIllegalFilenameChars(N, '_');
+
+  std::error_code EC =
+      sys::fs::createTemporaryFile(CleansedName, "dot", FD, Filename);
   if (EC) {
     errs() << "Error: " << EC.message() << "\n";
     return "";