Add option to dump CFGs in (simple) graphviz format during all passes.

Summary:
I noticed the BinaryFunction::viewGraph() method that hadn't been implemented
and decided I could use a simple DOT dumper for CFGs while working on the indirect
call optimization.

I've implemented the bare minimum for the dumper.  It's just nodes+BB labels with
dges. We can add more detailed information as needed/desired.

(cherry picked from FBD3509326)

bolt/BinaryFunction.cpp

@@ -24,6 +24,7 @@
 #include "llvm/Object/ObjectFile.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/GraphWriter.h"
 #include "llvm/Support/raw_ostream.h"
 #include <limits>
 #include <queue>
@@ -1316,6 +1317,76 @@ void BinaryFunction::modifyLayout(LayoutType Type, bool Split) {
   fixBranches();
 }
 
+namespace {
+
+#ifndef MAX_PATH
+#define MAX_PATH 255
+#endif
+
+std::string constructFilename(std::string Filename,
+                              std::string Annotation,
+                              std::string Suffix) {
+  std::replace(Filename.begin(), Filename.end(), '/', '-');
+  if (!Annotation.empty()) {
+    Annotation.insert(0, "-");
+  }
+  if (Filename.size() + Annotation.size() + Suffix.size() > MAX_PATH) {
+    assert(Suffix.size() + Annotation.size() <= MAX_PATH);
+    dbgs() << "BOLT-WARNING: Filename \"" << Filename << Annotation << Suffix
+           << "\" exceeds the " << MAX_PATH << " size limit, truncating.\n";
+    Filename.resize(MAX_PATH - (Suffix.size() + Annotation.size()));
+  }
+  Filename += Annotation;
+  Filename += Suffix;
+  return Filename;
+}
+
+}
+
+void BinaryFunction::dumpGraph(raw_ostream& OS) const {
+  OS << "strict digraph \"" << getName() << "\" {\n";
+  for (auto *BB : BasicBlocks) {
+    for (auto *Succ : BB->successors()) {
+      OS << "\"" << BB->getName() << "\" -> "
+         << "\"" << Succ->getName() << "\"\n";
+    }
+  }
+  OS << "}\n";
+}
+
+void BinaryFunction::viewGraph() const {
+  SmallString<MAX_PATH> Filename;
+  if (auto EC = sys::fs::createTemporaryFile("bolt-cfg", "dot", Filename)) {
+    dbgs() << "BOLT-WARNING: " << EC.message() << ", unable to create "
+           << " bolt-cfg-XXXXX.dot temporary file.\n";
+    return;
+  }
+  dumpGraphToFile(Filename.str());
+  if (DisplayGraph(Filename)) {
+    dbgs() << "BOLT-WARNING: Can't display " << Filename
+           << " with graphviz.\n";
+  }
+  if (auto EC = sys::fs::remove(Filename)) {
+    dbgs() << "BOLT-WARNING: " << EC.message() << ", failed to remove "
+           << Filename.str() << "\n";
+  }
+}
+
+void BinaryFunction::dumpGraphForPass(std::string Annotation) const {
+  dumpGraphToFile(constructFilename(getName(), Annotation, ".dot"));
+}
+
+void BinaryFunction::dumpGraphToFile(std::string Filename) const {
+  std::error_code EC;
+  raw_fd_ostream of(Filename, EC, sys::fs::F_None);
+  if (EC) {
+    dbgs() << "BOLT-WARNING: " << EC.message() << ", unable to open "
+           << Filename << " for output.\n";
+    return;
+  }
+  dumpGraph(of);
+}
+
 const BinaryBasicBlock *
 BinaryFunction::getOriginalLayoutSuccessor(const BinaryBasicBlock *BB) const {
   auto I = std::upper_bound(begin(), end(), *BB);

bolt/BinaryFunction.h

@@ -392,9 +392,20 @@ public:
   void modifyLayout(LayoutType Type, bool Split);
 
   /// View CFG in graphviz program
-  void viewGraph();
+  void viewGraph() const;
 
-  /// Get basic block index assuming it belongs to this function.
+  /// Dump CFG in graphviz format
+  void dumpGraph(raw_ostream& OS) const;
+
+  /// Dump CFG in graphviz format to file.
+  void dumpGraphToFile(std::string Filename) const;
+
+  /// Dump CFG in graphviz format to a file with a filename that is derived
+  /// from the function name and Annotation strings.  Useful for dumping the
+  /// CFG after an optimization pass.
+  void dumpGraphForPass(std::string Annotation = "") const;
+
+    /// Get basic block index assuming it belongs to this function.
   unsigned getIndex(const BinaryBasicBlock *BB) const {
     assert(BasicBlockIndices.find(BB) != BasicBlockIndices.end());
     return BasicBlockIndices.find(BB)->second;

bolt/BinaryPasses.cpp

@@ -17,6 +17,7 @@
 namespace opts {
 
 extern llvm::cl::opt<bool> PrintAll;
+extern llvm::cl::opt<bool> DumpDotAll;
 extern llvm::cl::opt<bool> PrintReordered;
 extern llvm::cl::opt<bool> PrintEHRanges;
 extern llvm::cl::opt<bool> PrintUCE;
@@ -343,6 +344,9 @@ void EliminateUnreachableBlocks::runOnFunction(BinaryFunction& Function) {
 
     if (opts::PrintAll || opts::PrintUCE)
       Function.print(errs(), "after unreachable code elimination", true);
+
+    if (opts::DumpDotAll)
+      Function.dumpGraphForPass("unreachable-code");
   }
 }
 
@@ -379,6 +383,8 @@ void ReorderBasicBlocks::runOnFunctions(
       Function.modifyLayout(opts::ReorderBlocks, ShouldSplit);
       if (opts::PrintAll || opts::PrintReordered)
         Function.print(errs(), "after reordering blocks", true);
+      if (opts::DumpDotAll)
+        Function.dumpGraphForPass("reordering");
     }
   }
 }
@@ -409,6 +415,8 @@ void FixupFunctions::runOnFunctions(
     Function.updateEHRanges();
     if (opts::PrintAll || opts::PrintEHRanges)
       Function.print(errs(), "after updating EH ranges", true);
+    if (opts::DumpDotAll)
+      Function.dumpGraphForPass("update-EH-ranges");
   }
 }
 
@@ -519,6 +527,9 @@ void SimplifyConditionalTailCalls::runOnFunctions(
       if (opts::PrintAll || opts::PrintReordered) {
         Function.print(errs(), "after tail call patching", true);
       }
+      if (opts::DumpDotAll) {
+        Function.dumpGraphForPass("tail-call-patching");
+      }
     }
   }
 

bolt/RewriteInstance.cpp

@@ -148,6 +148,11 @@ cl::opt<bool>
 PrintAll("print-all", cl::desc("print functions after each stage"),
          cl::Hidden);
 
+cl::opt<bool>
+DumpDotAll("dump-dot-all",
+           cl::desc("dump function CFGs to graphviz format after each stage"),
+           cl::Hidden);
+
 static cl::opt<bool>
 PrintCFG("print-cfg", cl::desc("print functions after CFG construction"),
          cl::Hidden);
@@ -913,6 +918,9 @@ void RewriteInstance::disassembleFunctions() {
     if (opts::PrintAll || opts::PrintCFG)
       Function.print(errs(), "after building cfg", true);
 
+    if (opts::DumpDotAll)
+      Function.dumpGraphForPass("build-cfg");
+
     TotalScore += Function.getFunctionScore();
 
   } // Iterate over all functions