Fix SelectionDAG Graph Printing on Windows

Currently, when compiling to IR (presumably at the clang level) LLVM
mangles symbols and sometimes they have illegal file characters
including `?`'s in them. This causes a problem when building a graph via
llc on Windows because the code currently passes the machine function
name all the way down to the Windows API which frequently returns error
123  **ERROR_INVALID_NAME**
https://docs.microsoft.com/en-us/windows/win32/debug/system-error-codes--0-499-

Thus, we need to remove those illegal characters from the machine
function name before generating a graph, which is the purpose of this
patch.
https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file

I've created a static helper function replace_illegal_filename_chars
which within GraphWriter.cpp to help with replacing illegal file
character names before generating a dot graph filename.

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D76863

llvm/include/llvm/Support/GraphWriter.h

@@ -330,11 +330,8 @@ std::string WriteGraph(const GraphType &G, const Twine &Name,
                        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);
 

llvm/lib/Support/GraphWriter.cpp

@@ -76,10 +76,35 @@ StringRef llvm::DOT::getColorString(unsigned ColorNumber) {
   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 (char IllegalChar : IllegalChars) {
+    std::replace(Filename.begin(), Filename.end(), IllegalChar,
+                 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 "";