Index: include/llvm/ProfileData/ProfileCommon.h
===================================================================
--- include/llvm/ProfileData/ProfileCommon.h
+++ include/llvm/ProfileData/ProfileCommon.h
@@ -21,6 +21,8 @@
 #define LLVM_PROFILEDATA_PROFILE_COMMON_H
 
 namespace llvm {
+class Function;
+class Module;
 namespace IndexedInstrProf {
 struct Summary;
 }
@@ -28,6 +30,8 @@
 class FunctionSamples;
 }
 struct InstrProfRecord;
+inline const char *getHotSectionPrefix() { return ".hot"; }
+inline const char *getUnlikelySectionPrefix() { return ".unlikely"; }
 // The profile summary is one or more (Cutoff, MinCount, NumCounts) triplets.
 // The semantics of counts depend on the type of profile. For instrumentation
 // profile, counts are block counts and for sample profile, counts are
@@ -66,6 +70,12 @@
 
 public:
   static const int Scale = 1000000;
+  // \brief Returns true if profile is available.
+  static bool hasProfile(const Module *M);
+  // \brief Returns true if F is a hot function.
+  static bool isFunctionHot(const Function *F);
+  // \brief Returns true if F is unlikley executed.
+  static bool isFunctionUnlikely(const Function *F);
   inline std::vector<ProfileSummaryEntry> &getDetailedSummary();
   void computeDetailedSummary();
   /// \brief A vector of useful cutoff values for detailed summary.
Index: lib/CodeGen/TargetLoweringObjectFileImpl.cpp
===================================================================
--- lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -34,6 +34,7 @@
 #include "llvm/MC/MCSymbolELF.h"
 #include "llvm/MC/MCValue.h"
 #include "llvm/ProfileData/InstrProf.h"
+#include "llvm/ProfileData/ProfileCommon.h"
 #include "llvm/Support/COFF.h"
 #include "llvm/Support/Dwarf.h"
 #include "llvm/Support/ELF.h"
@@ -244,6 +245,11 @@
   return ".data.rel.ro";
 }
 
+static cl::opt<bool> GroupFunctionsByHotness(
+    "group-functions-by-hotness",
+    llvm::cl::desc("Partition hot/cold functions by sections prefix"),
+    cl::init(false));
+
 static MCSectionELF *
 selectELFSectionForGlobal(MCContext &Ctx, const GlobalValue *GV,
                           SectionKind Kind, Mangler &Mang,
@@ -294,6 +300,16 @@
     Name = getSectionPrefixForGlobal(Kind);
   }
 
+  if (GroupFunctionsByHotness) {
+    if (const Function *F = dyn_cast<Function>(GV)) {
+      if (ProfileSummary::isFunctionHot(F)) {
+        Name += getHotSectionPrefix();
+      } else if (ProfileSummary::isFunctionUnlikely(F)) {
+        Name += getUnlikelySectionPrefix();
+      }
+    }
+  }
+
   if (EmitUniqueSection && UniqueSectionNames) {
     Name.push_back('.');
     TM.getNameWithPrefix(Name, GV, Mang, true);
Index: lib/ProfileData/ProfileSummary.cpp
===================================================================
--- lib/ProfileData/ProfileSummary.cpp
+++ lib/ProfileData/ProfileSummary.cpp
@@ -11,6 +11,9 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/IR/Attributes.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Module.h"
 #include "llvm/ProfileData/InstrProf.h"
 #include "llvm/ProfileData/ProfileCommon.h"
 #include "llvm/ProfileData/SampleProf.h"
@@ -75,6 +78,31 @@
   }
 }
 
+bool ProfileSummary::hasProfile(const Module *M) {
+  // FIXME: update when summary data is stored in module's metadata.
+  return false;
+}
+
+// Returns true if the function is a hot function.
+bool ProfileSummary::isFunctionHot(const Function *F) {
+  // FIXME: update when summary data is stored in module's metadata.
+  return false;
+}
+
+bool ProfileSummary::isFunctionUnlikely(const Function *F) {
+  if (F->hasFnAttribute(Attribute::Cold)) {
+    return true;
+  }
+  if (!hasProfile(F->getParent())) {
+    return false;
+  }
+  if (!F->getEntryCount()) {
+    return true;
+  }
+  // FIXME: update when summary data is stored in module's metadata.
+  return (*F->getEntryCount()) == 0;
+}
+
 InstrProfSummary::InstrProfSummary(const IndexedInstrProf::Summary &S)
     : ProfileSummary(), MaxInternalBlockCount(S.get(
                             IndexedInstrProf::Summary::MaxInternalBlockCount)),