Index: ProfileData/InstrProfData.inc
===================================================================
--- ProfileData/InstrProfData.inc
+++ ProfileData/InstrProfData.inc
@@ -700,9 +700,11 @@
  * version for other variants of profile. We set the lowest bit of the upper 8
  * bits (i.e. bit 56) to 1 to indicate if this is an IR-level instrumentaiton
  * generated profile, and 0 if this is a Clang FE generated profile.
-*/
+ */
 #define VARIANT_MASKS_ALL 0xff00000000000000ULL
 #define GET_VERSION(V) ((V) & ~VARIANT_MASKS_ALL)
+#define VARIANT_MASK_IR_PROF (0x1ULL << 56)
+#define IR_LEVEL_PROF_VERSION_VAR __llvm_profile_raw_version
 
 /* Runtime section names and name strings.  */
 #define INSTR_PROF_DATA_SECT_NAME __llvm_prf_data
Index: ProfileData/InstrProfReader.h
===================================================================
--- ProfileData/InstrProfReader.h
+++ ProfileData/InstrProfReader.h
@@ -64,6 +64,7 @@
   /// Iterator over profile data.
   InstrProfIterator begin() { return InstrProfIterator(this); }
   InstrProfIterator end() { return InstrProfIterator(); }
+  virtual bool isIRLevelProfile() const = 0;
 
   /// Return the PGO symtab. There are three different readers:
   /// Raw, Text, and Indexed profile readers. The first two types
@@ -118,6 +119,7 @@
   std::unique_ptr<MemoryBuffer> DataBuffer;
   /// Iterator over the profile data.
   line_iterator Line;
+  bool IsIRLevelProfile;
 
   TextInstrProfReader(const TextInstrProfReader &) = delete;
   TextInstrProfReader &operator=(const TextInstrProfReader &) = delete;
@@ -125,11 +127,14 @@
 
 public:
   TextInstrProfReader(std::unique_ptr<MemoryBuffer> DataBuffer_)
-      : DataBuffer(std::move(DataBuffer_)), Line(*DataBuffer, true, '#') {}
+      : DataBuffer(std::move(DataBuffer_)), Line(*DataBuffer, true, '#'),
+        IsIRLevelProfile(false) {}
 
   /// Return true if the given buffer is in text instrprof format.
   static bool hasFormat(const MemoryBuffer &Buffer);
 
+  bool isIRLevelProfile() const override { return IsIRLevelProfile; }
+
   /// Read the header.
   std::error_code readHeader() override;
   /// Read a single record.
@@ -154,6 +159,10 @@
   /// The profile data file contents.
   std::unique_ptr<MemoryBuffer> DataBuffer;
   bool ShouldSwapBytes;
+  // The value of the version field of the raw profile data header. The lower 56
+  // bits specifies the format version and the most significant 8 bits specify
+  // the variant types of the profile.
+  uint64_t Version;
   uint64_t CountersDelta;
   uint64_t NamesDelta;
   const RawInstrProf::ProfileData<IntPtrT> *Data;
@@ -176,6 +185,9 @@
   static bool hasFormat(const MemoryBuffer &DataBuffer);
   std::error_code readHeader() override;
   std::error_code readNextRecord(InstrProfRecord &Record) override;
+  bool isIRLevelProfile() const override {
+    return (Version & VARIANT_MASK_IR_PROF) != 0;
+  }
 
   InstrProfSymtab &getSymtab() override {
     assert(Symtab.get());
@@ -292,6 +304,7 @@
   virtual void setValueProfDataEndianness(support::endianness Endianness) = 0;
   virtual ~InstrProfReaderIndexBase() {}
   virtual uint64_t getVersion() const = 0;
+  virtual bool isIRLevelProfile() const = 0;
   virtual void populateSymtab(InstrProfSymtab &) = 0;
 };
 
@@ -323,7 +336,10 @@
     HashTable->getInfoObj().setValueProfDataEndianness(Endianness);
   }
   ~InstrProfReaderIndex() override {}
-  uint64_t getVersion() const override { return FormatVersion; }
+  uint64_t getVersion() const override { return GET_VERSION(FormatVersion); }
+  bool isIRLevelProfile() const override {
+    return (FormatVersion & VARIANT_MASK_IR_PROF) != 0;
+  }
   void populateSymtab(InstrProfSymtab &Symtab) override {
     Symtab.create(HashTable->keys());
   }
@@ -348,7 +364,9 @@
                                    const unsigned char *Cur);
 
 public:
+  /// Return the profile version.
   uint64_t getVersion() const { return Index->getVersion(); }
+  bool isIRLevelProfile() const override { return Index->isIRLevelProfile(); }
   IndexedInstrProfReader(std::unique_ptr<MemoryBuffer> DataBuffer)
       : DataBuffer(std::move(DataBuffer)), Index(nullptr) {}
 
Index: ProfileData/InstrProfWriter.h
===================================================================
--- ProfileData/InstrProfWriter.h
+++ ProfileData/InstrProfWriter.h
@@ -30,10 +30,12 @@
 class InstrProfWriter {
 public:
   typedef SmallDenseMap<uint64_t, InstrProfRecord, 1> ProfilingData;
+  enum ProfKind { PF_Unknown = 0, PF_FE, PF_IRLevel };
 
 private:
   bool Sparse;
   StringMap<ProfilingData> FunctionData;
+  ProfKind ProfileKind;
   // Use raw pointer here for the incomplete type object.
   InstrProfRecordWriterTrait *InfoObj;
 
@@ -55,6 +57,16 @@
   /// Write the profile, returning the raw data. For testing.
   std::unique_ptr<MemoryBuffer> writeBuffer();
 
+  /// Set the ProfileKind. Report error if mixing FE and IR level profiles.
+  std::error_code setIsIRLevelProfile(bool IsIRLevel) {
+    if (ProfileKind == PF_Unknown) {
+      ProfileKind = IsIRLevel ? PF_IRLevel: PF_FE;
+      return instrprof_error::success;
+    }
+    return (IsIRLevel == (ProfileKind == PF_IRLevel)) ?
+           instrprof_error::success : instrprof_error::unsupported_version;
+  }
+
   // Internal interface for testing purpose only.
   void setValueProfDataEndianness(support::endianness Endianness);
   void setOutputSparse(bool Sparse);