Utility to dump .dot representation of SelectionDAG without firing viewer

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.

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D80711

llvm/include/llvm/CodeGen/SelectionDAG.h

@@ -433,6 +433,17 @@ public:
   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.
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+  LLVM_DUMP_METHOD void dumpDotGraph(const Twine &FileName, const Twine &Title);
+#endif
+
   /// Pop up a GraphViz/gv window with the DAG rendered using 'dot'.
   void viewGraph(const std::string &Title);
   void viewGraph();

llvm/include/llvm/Support/GraphWriter.h

@@ -341,6 +341,8 @@ std::string WriteGraph(const GraphType &G, const Twine &Name,
     } 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);
@@ -356,6 +358,17 @@ std::string WriteGraph(const GraphType &G, const Twine &Name,
   return Filename;
 }
 
+/// DumpDotGraph - Just dump a dot graph to the user-provided file name.
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+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());
+}
+#endif
+
 /// ViewGraph - Emit a dot graph, run 'dot', run gv on the postscript file,
 /// then cleanup.  For use from the debugger.
 ///

llvm/lib/CodeGen/SelectionDAG/SelectionDAGPrinter.cpp

@@ -164,6 +164,20 @@ 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.
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+LLVM_DUMP_METHOD void SelectionDAG::dumpDotGraph(const Twine &FileName,
+                                                 const Twine &Title) {
+  dumpDotGraphToFile(this, FileName, Title);
+}
+#endif
+
 /// clearGraphAttrs - Clear all previously defined node graph attributes.
 /// Intended to be used from a debugging tool (eg. gdb).
 void SelectionDAG::clearGraphAttrs() {