Index: llvm/trunk/lib/Transforms/Instrumentation/CFGMST.h
===================================================================
--- llvm/trunk/lib/Transforms/Instrumentation/CFGMST.h
+++ llvm/trunk/lib/Transforms/Instrumentation/CFGMST.h
@@ -20,6 +20,7 @@
 #include "llvm/Analysis/BlockFrequencyInfo.h"
 #include "llvm/Analysis/BranchProbabilityInfo.h"
 #include "llvm/Analysis/CFG.h"
+#include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Support/BranchProbability.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
@@ -136,6 +137,21 @@
                      << " w = " << BBWeight << "\n");
       }
     }
+    // check if there is any infinite loop. If yes, add a fake edge from
+    // the header block to the fake node:
+    for (auto *L : *LI) {
+      SmallVector<BasicBlock *, 2> ExitingBlocks;
+      L->getExitingBlocks(ExitingBlocks);
+      if (!ExitingBlocks.empty())
+        continue;
+      auto *HB = L->getHeader();
+      if (!HB)
+        continue;
+      addEdge(HB, nullptr, UINT64_MAX);
+      DEBUG(dbgs() << "  Edge: from infinite loop header " 
+                   << HB->getName() << " to exit"
+                   << " w = " << UINT64_MAX << "\n");
+    }
   }
 
   // Sort CFG edges based on its weight.
@@ -212,11 +228,13 @@
 
   BranchProbabilityInfo *BPI;
   BlockFrequencyInfo *BFI;
+  LoopInfo *LI;
 
 public:
   CFGMST(Function &Func, BranchProbabilityInfo *BPI_ = nullptr,
-         BlockFrequencyInfo *BFI_ = nullptr)
-      : F(Func), BPI(BPI_), BFI(BFI_) {
+         BlockFrequencyInfo *BFI_ = nullptr,
+         LoopInfo *LI_ = nullptr)
+      : F(Func), BPI(BPI_), BFI(BFI_), LI(LI_) {
     buildEdges();
     sortEdgesByWeight();
     computeMinimumSpanningTree();
Index: llvm/trunk/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
+++ llvm/trunk/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
@@ -390,6 +390,7 @@
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.addRequired<BlockFrequencyInfoWrapperPass>();
+    AU.addRequired<LoopInfoWrapperPass>();
   }
 };
 
@@ -415,6 +416,7 @@
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.addRequired<BlockFrequencyInfoWrapperPass>();
+    AU.addRequired<LoopInfoWrapperPass>();
   }
 };
 
@@ -426,6 +428,7 @@
                       "PGO instrumentation.", false, false)
 INITIALIZE_PASS_DEPENDENCY(BlockFrequencyInfoWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(BranchProbabilityInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
 INITIALIZE_PASS_END(PGOInstrumentationGenLegacyPass, "pgo-instr-gen",
                     "PGO instrumentation.", false, false)
 
@@ -439,6 +442,7 @@
                       "Read PGO instrumentation profile.", false, false)
 INITIALIZE_PASS_DEPENDENCY(BlockFrequencyInfoWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(BranchProbabilityInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
 INITIALIZE_PASS_END(PGOInstrumentationUseLegacyPass, "pgo-instr-use",
                     "Read PGO instrumentation profile.", false, false)
 
@@ -530,9 +534,9 @@
       Function &Func,
       std::unordered_multimap<Comdat *, GlobalValue *> &ComdatMembers,
       bool CreateGlobalVar = false, BranchProbabilityInfo *BPI = nullptr,
-      BlockFrequencyInfo *BFI = nullptr)
+      BlockFrequencyInfo *BFI = nullptr, LoopInfo *LI = nullptr)
       : F(Func), ComdatMembers(ComdatMembers), ValueSites(IPVK_Last + 1),
-        SIVisitor(Func), MIVisitor(Func), MST(F, BPI, BFI) {
+        SIVisitor(Func), MIVisitor(Func), MST(F, BPI, BFI, LI) {
     // This should be done before CFG hash computation.
     SIVisitor.countSelects(Func);
     MIVisitor.countMemIntrinsics(Func);
@@ -715,9 +719,10 @@
 // Critical edges will be split.
 static void instrumentOneFunc(
     Function &F, Module *M, BranchProbabilityInfo *BPI, BlockFrequencyInfo *BFI,
+    LoopInfo *LI,
     std::unordered_multimap<Comdat *, GlobalValue *> &ComdatMembers) {
   FuncPGOInstrumentation<PGOEdge, BBInfo> FuncInfo(F, ComdatMembers, true, BPI,
-                                                   BFI);
+                                                   BFI, LI);
   unsigned NumCounters = FuncInfo.getNumCounters();
 
   uint32_t I = 0;
@@ -844,9 +849,10 @@
   PGOUseFunc(Function &Func, Module *Modu,
              std::unordered_multimap<Comdat *, GlobalValue *> &ComdatMembers,
              BranchProbabilityInfo *BPI = nullptr,
-             BlockFrequencyInfo *BFIin = nullptr)
+             BlockFrequencyInfo *BFIin = nullptr,
+             LoopInfo *LI = nullptr)
       : F(Func), M(Modu), BFI(BFIin),
-        FuncInfo(Func, ComdatMembers, false, BPI, BFIin),
+        FuncInfo(Func, ComdatMembers, false, BPI, BFIin, LI),
         FreqAttr(FFA_Normal) {}
 
   // Read counts for the instrumented BB from profile.
@@ -1379,7 +1385,8 @@
 
 static bool InstrumentAllFunctions(
     Module &M, function_ref<BranchProbabilityInfo *(Function &)> LookupBPI,
-    function_ref<BlockFrequencyInfo *(Function &)> LookupBFI) {
+    function_ref<BlockFrequencyInfo *(Function &)> LookupBFI,
+    function_ref<LoopInfo *(Function &)> LookupLI) {
   createIRLevelProfileFlagVariable(M);
   std::unordered_multimap<Comdat *, GlobalValue *> ComdatMembers;
   collectComdatMembers(M, ComdatMembers);
@@ -1389,7 +1396,8 @@
       continue;
     auto *BPI = LookupBPI(F);
     auto *BFI = LookupBFI(F);
-    instrumentOneFunc(F, &M, BPI, BFI, ComdatMembers);
+    auto *LI = LookupLI(F);
+    instrumentOneFunc(F, &M, BPI, BFI, LI, ComdatMembers);
   }
   return true;
 }
@@ -1404,7 +1412,10 @@
   auto LookupBFI = [this](Function &F) {
     return &this->getAnalysis<BlockFrequencyInfoWrapperPass>(F).getBFI();
   };
-  return InstrumentAllFunctions(M, LookupBPI, LookupBFI);
+  auto LookupLI = [this](Function &F) {
+    return &this->getAnalysis<LoopInfoWrapperPass>(F).getLoopInfo();
+  };
+  return InstrumentAllFunctions(M, LookupBPI, LookupBFI, LookupLI);
 }
 
 PreservedAnalyses PGOInstrumentationGen::run(Module &M,
@@ -1418,7 +1429,11 @@
     return &FAM.getResult<BlockFrequencyAnalysis>(F);
   };
 
-  if (!InstrumentAllFunctions(M, LookupBPI, LookupBFI))
+  auto LookupLI = [&FAM](Function &F) {
+    return &FAM.getResult<LoopAnalysis>(F);
+  };
+
+  if (!InstrumentAllFunctions(M, LookupBPI, LookupBFI, LookupLI))
     return PreservedAnalyses::all();
 
   return PreservedAnalyses::none();
@@ -1427,7 +1442,8 @@
 static bool annotateAllFunctions(
     Module &M, StringRef ProfileFileName,
     function_ref<BranchProbabilityInfo *(Function &)> LookupBPI,
-    function_ref<BlockFrequencyInfo *(Function &)> LookupBFI) {
+    function_ref<BlockFrequencyInfo *(Function &)> LookupBFI,
+    function_ref<LoopInfo *(Function &)> LookupLI) {
   DEBUG(dbgs() << "Read in profile counters: ");
   auto &Ctx = M.getContext();
   // Read the counter array from file.
@@ -1463,7 +1479,8 @@
       continue;
     auto *BPI = LookupBPI(F);
     auto *BFI = LookupBFI(F);
-    PGOUseFunc Func(F, &M, ComdatMembers, BPI, BFI);
+    auto *LI = LookupLI(F);
+    PGOUseFunc Func(F, &M, ComdatMembers, BPI, BFI, LI);
     if (!Func.readCounters(PGOReader.get()))
       continue;
     Func.populateCounters();
@@ -1539,7 +1556,11 @@
     return &FAM.getResult<BlockFrequencyAnalysis>(F);
   };
 
-  if (!annotateAllFunctions(M, ProfileFileName, LookupBPI, LookupBFI))
+  auto LookupLI = [&FAM](Function &F) {
+    return &FAM.getResult<LoopAnalysis>(F);
+  };
+
+  if (!annotateAllFunctions(M, ProfileFileName, LookupBPI, LookupBFI, LookupLI))
     return PreservedAnalyses::all();
 
   return PreservedAnalyses::none();
@@ -1555,8 +1576,11 @@
   auto LookupBFI = [this](Function &F) {
     return &this->getAnalysis<BlockFrequencyInfoWrapperPass>(F).getBFI();
   };
+  auto LookupLI = [this](Function &F) {
+    return &this->getAnalysis<LoopInfoWrapperPass>(F).getLoopInfo();
+  };
 
-  return annotateAllFunctions(M, ProfileFileName, LookupBPI, LookupBFI);
+  return annotateAllFunctions(M, ProfileFileName, LookupBPI, LookupBFI, LookupLI);
 }
 
 static std::string getSimpleNodeName(const BasicBlock *Node) {
Index: llvm/trunk/test/Transforms/PGOProfile/infinite_loop_gen.ll
===================================================================
--- llvm/trunk/test/Transforms/PGOProfile/infinite_loop_gen.ll
+++ llvm/trunk/test/Transforms/PGOProfile/infinite_loop_gen.ll
@@ -0,0 +1,18 @@
+; RUN: opt < %s -pgo-instr-gen -S -o -   | FileCheck %s
+
+define void @foo() {
+entry:
+  br label %while.body
+; CHECK: llvm.instrprof.increment
+
+  while.body:                                       ; preds = %entry, %while.body
+; CHECK: llvm.instrprof.increment
+    call void (...) @bar() #2
+    br label %while.body
+}
+
+declare void @bar(...)
+
+
+attributes #0 = { nounwind }
+