[BOLT] Add -dump-cg option to dump call graph

[rafauler]

LGTM

bolt/include/bolt/Passes/CallGraph.h

public:
   }
 
   // Initialize NormalizedWeight field for every arc
   void normalizeArcWeights();
   // Make sure that the sum of incoming arc weights is at least the number of
   // samples for every node
   void adjustArcWeights();
 
-  template <typename L> void printDot(char *fileName, L getLabel) const;
+  template <typename L> void printDot(StringRef FileName, L getLabel) const;
 
 private:
   void setSamples(const NodeId Id, uint64_t Samples) {
     assert(Id < Nodes.size());
     Nodes[Id].Samples = Samples;
   }
 
   std::vector<Node> Nodes;
   ArcsType Arcs;
 };
 
-template <class L> void CallGraph::printDot(char *FileName, L GetLabel) const {
+template <class L>
+void CallGraph::printDot(StringRef FileName, L GetLabel) const {
   std::error_code EC;
-  raw_fd_ostream OS(std::string(FileName), EC, sys::fs::OF_None);
+  raw_fd_ostream OS(FileName, EC, sys::fs::OF_None);
   if (EC)
     return;
 
   OS << "digraph g {\n";
   for (NodeId F = 0; F < Nodes.size(); F++) {
     if (Nodes[F].samples() == 0)
       continue;
     OS << "f" << F << " [label=\"" << GetLabel(F)

bolt/lib/Passes/BinaryFunctionCallGraph.cpp

 #include "bolt/Core/BinaryContext.h"
 #include "bolt/Core/BinaryFunction.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Timer.h"
 #include <stack>
 
 #define DEBUG_TYPE "callgraph"
 
+using namespace llvm;
+
 namespace opts {
-extern llvm::cl::opt<bool> TimeOpts;
-extern llvm::cl::opt<unsigned> Verbosity;
+
+extern cl::opt<bool> TimeOpts;
+extern cl::opt<unsigned> Verbosity;
+extern cl::OptionCategory BoltCategory;
+
+static cl::opt<std::string>
+    DumpCGDot("dump-cg", cl::desc("dump callgraph to the given file"),
+              cl::cat(BoltCategory));
+
 } // namespace opts
 
 namespace llvm {
 namespace bolt {
 
 CallGraph::NodeId BinaryFunctionCallGraph::addNode(BinaryFunction *BF,
                                                    uint32_t Size,
                                                    uint64_t Samples) {
if (PrintInfo || opts::Verbosity > 0)
     outs() << format("BOLT-INFO: buildCallGraph: %u nodes, %u callsites "
                      "(%u recursive), density = %.6lf, %u callsites not "
                      "processed, %u callsites with invalid profile, "
                      "used perf data for %u stale functions.\n",
                      Cg.numNodes(), TotalCallsites, RecursiveCallsites,
                      Cg.density(), NotProcessed, NoProfileCallsites,
                      NumFallbacks);
 
+  if (opts::DumpCGDot.getNumOccurrences()) {
+    Cg.printDot(opts::DumpCGDot, [&](CallGraph::NodeId Id) {
+      return Cg.nodeIdToFunc(Id)->getPrintName();
+    });
+  }
+
   return Cg;
 }
 
 } // namespace bolt
 } // namespace llvm

bolt/lib/Utils/CommandLineOpts.cpp

cl::opt<bool> SplitEH("split-eh", cl::desc("split C++ exception handling code"),
                       cl::Hidden, cl::cat(BoltOptCategory));
 
 cl::opt<bool>
     StrictMode("strict",
                cl::desc("trust the input to be from a well-formed source"),
 
                cl::cat(BoltCategory));
 
-llvm::cl::opt<bool> TimeOpts("time-opts",
-                             cl::desc("print time spent in each optimization"),
-                             cl::cat(BoltOptCategory));
+cl::opt<bool> TimeOpts("time-opts",
 
 cl::opt<bool> UseOldText(
     "use-old-text",
     cl::desc("re-use space in old .text if possible (relocation mode)"),
     cl::cat(BoltCategory));
 
 cl::opt<bool> UpdateDebugSections(
     "update-debug-sections",