diff --git a/include/llvm/CodeGen/MachineBlockFrequencyInfo.h b/include/llvm/CodeGen/MachineBlockFrequencyInfo.h
index a9c7bf7dbc6..2bd51e8a75d 100644
--- a/include/llvm/CodeGen/MachineBlockFrequencyInfo.h
+++ b/include/llvm/CodeGen/MachineBlockFrequencyInfo.h
@@ -1,4 +1,4 @@
-//====----- MachineBlockFrequencyInfo.h - MachineBlock Frequency Analysis ----====//
+//====-- MachineBlockFrequencyInfo.h - MBB Frequency Analysis -*- C++ -*--====//
 //
 //                     The LLVM Compiler Infrastructure
 //
@@ -49,6 +49,9 @@ public:
   /// the other block frequencies. We do this to avoid using of floating points.
   ///
   BlockFrequency getBlockFreq(const MachineBasicBlock *MBB) const;
+
+  MachineFunction *getFunction() const;
+  void view() const;
 };
 
 }
diff --git a/lib/CodeGen/MachineBlockFrequencyInfo.cpp b/lib/CodeGen/MachineBlockFrequencyInfo.cpp
index e269d24e1d5..f3d7c80cef7 100644
--- a/lib/CodeGen/MachineBlockFrequencyInfo.cpp
+++ b/lib/CodeGen/MachineBlockFrequencyInfo.cpp
@@ -16,9 +16,93 @@
 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/InitializePasses.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/GraphWriter.h"
 
 using namespace llvm;
 
+#ifndef NDEBUG
+enum GVDAGType {
+  GVDT_None,
+  GVDT_Fraction,
+  GVDT_Integer
+};
+
+static cl::opt<GVDAGType>
+ViewMachineBlockFreqPropagationDAG("view-machine-block-freq-propagation-dags",
+                                   cl::Hidden,
+          cl::desc("Pop up a window to show a dag displaying how machine block "
+                   "frequencies propgate through the CFG."),
+          cl::values(
+            clEnumValN(GVDT_None, "none",
+                       "do not display graphs."),
+            clEnumValN(GVDT_Fraction, "fraction", "display a graph using the "
+                       "fractional block frequency representation."),
+            clEnumValN(GVDT_Integer, "integer", "display a graph using the raw "
+                       "integer fractional block frequency representation."),
+            clEnumValEnd));
+
+namespace llvm {
+
+template <>
+struct GraphTraits<MachineBlockFrequencyInfo *> {
+  typedef const MachineBasicBlock NodeType;
+  typedef MachineBasicBlock::const_succ_iterator ChildIteratorType;
+  typedef MachineFunction::const_iterator nodes_iterator;
+
+  static inline const NodeType *getEntryNode(const MachineBlockFrequencyInfo *G) {
+    return G->getFunction()->begin();
+  }
+  static ChildIteratorType child_begin(const NodeType *N) {
+    return N->succ_begin();
+  }
+  static ChildIteratorType child_end(const NodeType *N) {
+    return N->succ_end();
+  }
+  static nodes_iterator nodes_begin(const MachineBlockFrequencyInfo *G) {
+    return G->getFunction()->begin();
+  }
+  static nodes_iterator nodes_end(const MachineBlockFrequencyInfo *G) {
+    return G->getFunction()->end();
+  }
+};
+
+template<>
+struct DOTGraphTraits<MachineBlockFrequencyInfo*> : public DefaultDOTGraphTraits {
+  explicit DOTGraphTraits(bool isSimple=false) :
+    DefaultDOTGraphTraits(isSimple) {}
+
+  static std::string getGraphName(const MachineBlockFrequencyInfo *G) {
+    return G->getFunction()->getName();
+  }
+
+  std::string getNodeLabel(const MachineBasicBlock *Node,
+                           const MachineBlockFrequencyInfo *Graph) {
+    std::string Result;
+    raw_string_ostream OS(Result);
+
+    OS << Node->getName().str() << ":";
+    switch (ViewMachineBlockFreqPropagationDAG) {
+    case GVDT_Fraction:
+      Graph->getBlockFreq(Node).print(OS);
+      break;
+    case GVDT_Integer:
+      OS << Graph->getBlockFreq(Node).getFrequency();
+      break;
+    case GVDT_None:
+      llvm_unreachable("If we are not supposed to render a graph we should "
+                       "never reach this point.");
+    }
+
+    return Result;
+  }
+};
+
+
+} // end namespace llvm
+#endif
+
 INITIALIZE_PASS_BEGIN(MachineBlockFrequencyInfo, "machine-block-freq",
                       "Machine Block Frequency Analysis", true, true)
 INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfo)
@@ -47,10 +131,33 @@ void MachineBlockFrequencyInfo::getAnalysisUsage(AnalysisUsage &AU) const {
 bool MachineBlockFrequencyInfo::runOnMachineFunction(MachineFunction &F) {
   MachineBranchProbabilityInfo &MBPI = getAnalysis<MachineBranchProbabilityInfo>();
   MBFI->doFunction(&F, &MBPI);
+#ifndef NDEBUG
+  if (ViewMachineBlockFreqPropagationDAG != GVDT_None) {
+    view();
+  }
+#endif
   return false;
 }
 
+/// Pop up a ghostview window with the current block frequency propagation
+/// rendered using dot.
+void MachineBlockFrequencyInfo::view() const {
+// This code is only for debugging.
+#ifndef NDEBUG
+  ViewGraph(const_cast<MachineBlockFrequencyInfo *>(this),
+            "MachineBlockFrequencyDAGs");
+#else
+  errs() << "BlockFrequencyInfo::view is only available in debug builds on "
+            "systems with Graphviz or gv!\n";
+#endif // NDEBUG
+}
+
 BlockFrequency MachineBlockFrequencyInfo::
 getBlockFreq(const MachineBasicBlock *MBB) const {
   return MBFI->getBlockFreq(MBB);
 }
+
+MachineFunction *MachineBlockFrequencyInfo::getFunction() const {
+  return MBFI->Fn;
+}
+