diff --git a/include/llvm/Analysis/BlockFrequencyInfo.h b/include/llvm/Analysis/BlockFrequencyInfo.h
index 64bd15c9065..a123d0b8c13 100644
--- a/include/llvm/Analysis/BlockFrequencyInfo.h
+++ b/include/llvm/Analysis/BlockFrequencyInfo.h
@@ -41,6 +41,8 @@ public:
 
   bool runOnFunction(Function &F);
   void print(raw_ostream &O, const Module *M) const;
+  const Function *getFunction() const;
+  void view() const;
 
   /// getblockFreq - Return block frequency. Return 0 if we don't have the
   /// information. Please note that initial frequency is equal to ENTRY_FREQ. It
diff --git a/lib/Analysis/BlockFrequencyInfo.cpp b/lib/Analysis/BlockFrequencyInfo.cpp
index 541404d91b5..62f3ab16ca7 100644
--- a/lib/Analysis/BlockFrequencyInfo.cpp
+++ b/lib/Analysis/BlockFrequencyInfo.cpp
@@ -17,9 +17,92 @@
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/Passes.h"
 #include "llvm/InitializePasses.h"
+#include "llvm/Support/CFG.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>
+ViewBlockFreqPropagationDAG("view-block-freq-propagation-dags", cl::Hidden,
+          cl::desc("Pop up a window to show a dag displaying how block "
+                   "frequencies propagation 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<BlockFrequencyInfo *> {
+  typedef const BasicBlock NodeType;
+  typedef succ_const_iterator ChildIteratorType;
+  typedef Function::const_iterator nodes_iterator;
+
+  static inline const NodeType *getEntryNode(const BlockFrequencyInfo *G) {
+    return G->getFunction()->begin();
+  }
+  static ChildIteratorType child_begin(const NodeType *N) {
+    return succ_begin(N);
+  }
+  static ChildIteratorType child_end(const NodeType *N) {
+    return succ_end(N);
+  }
+  static nodes_iterator nodes_begin(const BlockFrequencyInfo *G) {
+    return G->getFunction()->begin();
+  }
+  static nodes_iterator nodes_end(const BlockFrequencyInfo *G) {
+    return G->getFunction()->end();
+  }
+};
+
+template<>
+struct DOTGraphTraits<BlockFrequencyInfo*> : public DefaultDOTGraphTraits {
+  explicit DOTGraphTraits(bool isSimple=false) :
+    DefaultDOTGraphTraits(isSimple) {}
+
+  static std::string getGraphName(const BlockFrequencyInfo *G) {
+    return G->getFunction()->getName();
+  }
+
+  std::string getNodeLabel(const BasicBlock *Node,
+                           const BlockFrequencyInfo *Graph) {
+    std::string Result;
+    raw_string_ostream OS(Result);
+
+    OS << Node->getName().str() << ":";
+    switch (ViewBlockFreqPropagationDAG) {
+    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(BlockFrequencyInfo, "block-freq",
                       "Block Frequency Analysis", true, true)
 INITIALIZE_PASS_DEPENDENCY(BranchProbabilityInfo)
@@ -46,6 +129,10 @@ void BlockFrequencyInfo::getAnalysisUsage(AnalysisUsage &AU) const {
 bool BlockFrequencyInfo::runOnFunction(Function &F) {
   BranchProbabilityInfo &BPI = getAnalysis<BranchProbabilityInfo>();
   BFI->doFunction(&F, &BPI);
+#ifndef NDEBUG
+  if (ViewBlockFreqPropagationDAG != GVDT_None)
+    view();
+#endif
   return false;
 }
 
@@ -56,3 +143,19 @@ void BlockFrequencyInfo::print(raw_ostream &O, const Module *) const {
 BlockFrequency BlockFrequencyInfo::getBlockFreq(const BasicBlock *BB) const {
   return BFI->getBlockFreq(BB);
 }
+
+/// Pop up a ghostview window with the current block frequency propagation
+/// rendered using dot.
+void BlockFrequencyInfo::view() const {
+// This code is only for debugging.
+#ifndef NDEBUG
+  ViewGraph(const_cast<BlockFrequencyInfo *>(this), "BlockFrequencyDAGs");
+#else
+  errs() << "BlockFrequencyInfo::view is only available in debug builds on "
+            "systems with Graphviz or gv!\n";
+#endif // NDEBUG
+}
+
+const Function *BlockFrequencyInfo::getFunction() const {
+  return BFI->Fn;
+}