Utility to dump .dot representation of SelectionDAG without firing viewer

[madhur13490]

Summary

This patch adds support for dumping .dot
representation of SelectionDAG. It is inspired from the fact that,
a developer may want to just dump the graph at
a predictable path with a simple name to compare.
The exisitng utility (i.e. viewGraph) are overkill
for this motive hence this patch adds the requires support
while using the core routines from GraphWriter.

Example usage: DAG.dumpDotGraph("/tmp/graph.dot", "MyGraph")
will create /tmp/graph.dot file when DAG is an
object of SelectionDAG class.

[madhur13490]

Update summary

[arsenm]

llvm/include/llvm/CodeGen/SelectionDAG.h

442

I would expect the filename to be a StringRef (I guess debuggers struggle more with this, and the others are using std::string)

llvm/include/llvm/Support/GraphWriter.h

344–345

The existing done I think was sufficient

366–369

Don't see the point of getting the return string and check if it's empty?

llvm/lib/CodeGen/SelectionDAG/SelectionDAGPrinter.cpp

171

Should this fully remove the code depending on LLVM_ENABLE_DUMP? Also the declaration should get LLVM_DUMP_METHOD?

[madhur13490]

llvm/include/llvm/CodeGen/SelectionDAG.h

442

In fact, I am preferring Twine here because I may want to concat input function name, code function name and some state. e.g filename = MachineFunction.getName() + "LowerCall"+"start" to indicate DAG for machine function in LowerCall at the start!

llvm/include/llvm/Support/GraphWriter.h

344–345

No, just "done" doesn't indicate who's and what's done? There has to be some context to it and it is present with view* methods. So, I'd prefer emitting more verbose text.

366–369

Yeah. Removed.

llvm/lib/CodeGen/SelectionDAG/SelectionDAGPrinter.cpp

171

Sure, the method will be more accessible in that way.

[madhur13490]

Addressing comments by arsenm

[madhur13490]

Fix clang-tidy errors

[arsenm]

llvm/lib/CodeGen/SelectionDAG/SelectionDAGPrinter.cpp

178–179

I think having anything here defeats the point of having a compile time way to remove the function. The function should not be present in the build at all without LLVM_ENABLE_DUMP

[madhur13490]

Address further comment by arsenm

[madhur13490]

llvm/lib/CodeGen/SelectionDAG/SelectionDAGPrinter.cpp

178–179

Yes, done.

[madhur13490]

rebase

[arsenm]

LGTM with nit

llvm/include/llvm/Support/GraphWriter.h

345

Remove the word "the"

llvm/include/llvm/CodeGen/SelectionDAG.h

public:
   const TargetLibraryInfo &getLibInfo() const { return *LibInfo; }
   const SelectionDAGTargetInfo &getSelectionDAGInfo() const { return *TSI; }
   const LegacyDivergenceAnalysis *getDivergenceAnalysis() const { return DA; }
   LLVMContext *getContext() const { return Context; }
   OptimizationRemarkEmitter &getORE() const { return *ORE; }
   ProfileSummaryInfo *getPSI() const { return PSI; }
   BlockFrequencyInfo *getBFI() const { return BFI; }
 
+  /// Just dump dot graph to a user-provided path and title.
+  /// This doesn't open the dot viewer program and
+  /// helps visualization when outside debugging session.
+  /// FileName expects absolute path. If provided
+  /// without any path separators then the file
+  /// will be created in the current directory.
+  /// Error will be emitted if the path is insane.
+  void dumpDotGraph(const Twine &FileName, const Twine &Title);
+
   /// Pop up a GraphViz/gv window with the DAG rendered using 'dot'.
   void viewGraph(const std::string &Title);
   void viewGraph();
 
 #ifndef NDEBUG
   std::map<const SDNode *, std::string> NodeGraphAttrs;
 #endif
 

llvm/include/llvm/Support/GraphWriter.h

if (Filename.empty()) {
     std::error_code EC = sys::fs::openFileForWrite(Filename, FD);
 
     // Writing over an existing file is not considered an error.
     if (EC == std::errc::file_exists) {
       errs() << "file exists, overwriting" << "\n";
     } else if (EC) {
       errs() << "error writing into file" << "\n";
       return "";
+    } else {
+      errs() << "writing to the newly created file " << Filename << "\n";
     }
   }
   raw_fd_ostream O(FD, /*shouldClose=*/ true);
 
   if (FD == -1) {
     errs() << "error opening file '" << Filename << "' for writing!\n";
     return "";
   }
 
   llvm::WriteGraph(O, G, ShortNames, Title);
   errs() << " done. \n";
 
   return Filename;
 }
 
+/// DumpDotGraph - Just dump a dot graph to the user-provided file name.
+template <typename GraphType>
+LLVM_DUMP_METHOD void
+dumpDotGraphToFile(const GraphType &G, const Twine &FileName,
+                   const Twine &Title, bool ShortNames = false,
+                   const Twine &Name = "") {
+  llvm::WriteGraph(G, Name, ShortNames, Title, FileName.str());
+}
+
 /// ViewGraph - Emit a dot graph, run 'dot', run gv on the postscript file,
 /// then cleanup.  For use from the debugger.
 ///
 template<typename GraphType>
 void ViewGraph(const GraphType &G, const Twine &Name,
                bool ShortNames = false, const Twine &Title = "",
                GraphProgram::Name Program = GraphProgram::DOT) {
   std::string Filename = llvm::WriteGraph(G, Name, ShortNames, Title);

llvm/lib/CodeGen/SelectionDAG/SelectionDAGPrinter.cpp

 }
 
 // This overload is defined out-of-line here instead of just using a
 // default parameter because this is easiest for gdb to call.
 void SelectionDAG::viewGraph() {
   viewGraph("");
 }
 
+/// Just dump dot graph to a user-provided path and title.
+/// This doesn't open the dot viewer program and
+/// helps visualization when outside debugging session.
+/// FileName expects absolute path. If provided
+/// without any path separators then the file
+/// will be created in the current directory.
+/// Error will be emitted if the path is insane.
+void SelectionDAG::dumpDotGraph(const Twine &FileName, const Twine &Title) {
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+  dumpDotGraphToFile(this, FileName, Title);
+#else
+  errs() << "SelectionDAG::DumpDotGraph is only available in debug builds or "
+         << "when LLVM_ENABLE_DUMP is ON.\n";
+#endif // NDEBUG
+}
+
 /// clearGraphAttrs - Clear all previously defined node graph attributes.
 /// Intended to be used from a debugging tool (eg. gdb).
 void SelectionDAG::clearGraphAttrs() {
 #ifndef NDEBUG
   NodeGraphAttrs.clear();
 #else
   errs() << "SelectionDAG::clearGraphAttrs is only available in debug builds"
          << " on systems with Graphviz or gv!\n";