Index: llvm/include/llvm/CodeGen/MIRFSDiscriminator.h
===================================================================
--- llvm/include/llvm/CodeGen/MIRFSDiscriminator.h
+++ llvm/include/llvm/CodeGen/MIRFSDiscriminator.h
@@ -48,10 +48,10 @@
 
 public:
   static char ID;
-  /// FS bits that will be used in this pass (numbers are 0 based and
-  /// inclusive).
-  MIRAddFSDiscriminators(unsigned LowBit = 0, unsigned HighBit = 0)
-      : MachineFunctionPass(ID), LowBit(LowBit), HighBit(HighBit) {
+  /// PassNum is the sequence number this pass is called, start from 1.
+  MIRAddFSDiscriminators(unsigned PassNum = 1) : MachineFunctionPass(ID) {
+    LowBit = getFSPassBitBegin(PassNum);
+    HighBit = getFSPassBitEnd(PassNum);
     assert(LowBit < HighBit && "HighBit needs to be greater than Lowbit");
   }
 
Index: llvm/include/llvm/CodeGen/Passes.h
===================================================================
--- llvm/include/llvm/CodeGen/Passes.h
+++ llvm/include/llvm/CodeGen/Passes.h
@@ -490,9 +490,9 @@
   /// Create IR Type Promotion pass. \see TypePromotion.cpp
   FunctionPass *createTypePromotionPass();
 
-  /// Add Flow Sensitive Discriminators.
-  FunctionPass *createMIRAddFSDiscriminatorsPass(unsigned LowBit,
-                                                 unsigned HighBit);
+  /// Add Flow Sensitive Discriminators. PassNum specifies the
+  /// sequence number of this pass (starting from 1).
+  FunctionPass *createMIRAddFSDiscriminatorsPass(unsigned PassNum);
 
   /// Creates MIR Debugify pass. \see MachineDebugify.cpp
   ModulePass *createDebugifyMachineModulePass();
Index: llvm/include/llvm/IR/DebugInfoMetadata.h
===================================================================
--- llvm/include/llvm/IR/DebugInfoMetadata.h
+++ llvm/include/llvm/IR/DebugInfoMetadata.h
@@ -1741,7 +1741,7 @@
   }
 
   /// Return the bits used for base discriminators.
-  static unsigned getBaseDiscriminatorBits() { return BASE_DIS_BIT_END; }
+  static unsigned getBaseDiscriminatorBits() { return getBaseFSBitEnd(); }
 
   /// Returns the base discriminator for a given encoded discriminator \p D.
   static unsigned getBaseDiscriminatorFromDiscriminator(unsigned D) {
Index: llvm/include/llvm/ProfileData/SampleProf.h
===================================================================
--- llvm/include/llvm/ProfileData/SampleProf.h
+++ llvm/include/llvm/ProfileData/SampleProf.h
@@ -190,7 +190,10 @@
   SecFlagPartial = (1 << 0),
   /// SecFlagContext means this is context-sensitive profile for
   /// CSSPGO
-  SecFlagFullContext = (1 << 1)
+  SecFlagFullContext = (1 << 1),
+  /// SecFlagFSDiscriminator means this profile uses flow-sensitive
+  /// discriminators.
+  SecFlagFSDiscriminator = (1 << 2)
 };
 
 enum class SecFuncMetadataFlags : uint32_t {
@@ -891,6 +894,9 @@
   /// Whether the profile contains any ".__uniq." suffix in a name.
   static bool HasUniqSuffix;
 
+  /// If this profile uses flow sensitive discriminators.
+  static bool ProfileIsFS;
+
   /// GUIDToFuncNameMap saves the mapping from GUID to the symbol name, for
   /// all the function symbols defined or declared in current module.
   DenseMap<uint64_t, StringRef> *GUIDToFuncNameMap = nullptr;
Index: llvm/include/llvm/ProfileData/SampleProfReader.h
===================================================================
--- llvm/include/llvm/ProfileData/SampleProfReader.h
+++ llvm/include/llvm/ProfileData/SampleProfReader.h
@@ -236,6 +236,7 @@
 #include "llvm/ProfileData/GCOV.h"
 #include "llvm/ProfileData/SampleProf.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/Discriminator.h"
 #include "llvm/Support/ErrorOr.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/SymbolRemappingReader.h"
@@ -350,6 +351,22 @@
   /// Read and validate the file header.
   virtual std::error_code readHeader() = 0;
 
+  /// Set the bits for FS discriminators. Parameter Pass specify the sequence
+  /// number, Pass == i is for the i-th round of adding FS discriminators.
+  /// Pass == 0 is for using base discriminators.
+  void setDiscriminatorMaskedBitFrom(uint32_t Pass) {
+    MaskedBitFrom = getFSPassBitEnd(Pass);
+  }
+
+  /// Get the bitmask the discriminators: For FS profiles, return the bit
+  /// mask for this pass. For non FS profiles, return (unsigned) -1.
+  uint32_t getDiscriminatorMask() const {
+    if (!ProfileIsFS)
+      return 0xFFFFFFFF;
+    assert((MaskedBitFrom != 0) && "MaskedBitFrom is not set properly");
+    return getN1Bits(MaskedBitFrom);
+  }
+
   /// The interface to read sample profiles from the associated file.
   std::error_code read() {
     if (std::error_code EC = readImpl())
@@ -505,6 +522,9 @@
   /// Number of context-sensitive profiles.
   uint32_t CSProfileCount = 0;
 
+  /// Whether the function profiles use FS discriminators.
+  bool ProfileIsFS = false;
+
   /// \brief The format of sample.
   SampleProfileFormat Format = SPF_None;
 
@@ -512,6 +532,10 @@
   /// is used by compiler. If SampleProfileReader is used by other
   /// tools which are not compiler, M is usually nullptr.
   const Module *M = nullptr;
+
+  /// Zero out the discriminator bits higher than bit MaskedBitFrom (0 based).
+  /// The default is to keep all the bits.
+  uint32_t MaskedBitFrom = 31;
 };
 
 class SampleProfileReaderText : public SampleProfileReader {
Index: llvm/include/llvm/Support/Discriminator.h
===================================================================
--- llvm/include/llvm/Support/Discriminator.h
+++ llvm/include/llvm/Support/Discriminator.h
@@ -13,6 +13,9 @@
 #ifndef LLVM_SUPPORT_DISCRIMINATOR_H
 #define LLVM_SUPPORT_DISCRIMINATOR_H
 
+#include "llvm/Support/Error.h"
+#include <assert.h>
+
 // Utility functions for encoding / decoding discriminators.
 /// With a given unsigned int \p U, use up to 13 bits to represent it.
 /// old_bit 1~5  --> new_bit 1~5
@@ -48,26 +51,65 @@
 }
 
 // Some constants used in FS Discriminators.
-#define BASE_DIS_BIT_BEG 0
-#define BASE_DIS_BIT_END 7
+//
+// The number of bits reserved for the base discrimininator. The base
+// discriminaitor starts from bit 0.
+static const unsigned BaseDiscriminatorBitWidth = 8;
+
+// The number of bits reserved for each FS discriminator pass.
+static const unsigned FSDiscriminatorBitWidth = 6;
+
+// The number of passes for FS discriminators. Note that the total
+// number of discriminaitor bits, i.e.
+// BaseDiscriminatorBitWidth
+//  + FSDiscriminatorBitWidth * NumPassOfFSDiscriminator
+// needs to fit in an unsigned int type.
+static const unsigned NumPassOfFSDiscriminator = 4;
+
+// Return the number of FS passes, excluding the pass adding the base
+// discriminators.
+static inline unsigned getNumFSPasses() { return NumPassOfFSDiscriminator; }
+
+// Return the ending bit for the i-th FS pass.
+static inline unsigned getFSPassBitEnd(unsigned I) {
+  assert(I <= NumPassOfFSDiscriminator &&
+         "Invalid FS discriminator pass number.");
+  return BaseDiscriminatorBitWidth + I * FSDiscriminatorBitWidth - 1;
+}
+
+// Return the begining bit for the i-th FS pass.
+static inline unsigned getFSPassBitBegin(unsigned I) {
+  assert(I > 0 && "I == 0 is reservered for the base discriminator pass.");
+  assert(I <= NumPassOfFSDiscriminator &&
+         "Invalid FS discriminator pass number.");
+  return getFSPassBitEnd(I - 1) + 1;
+}
 
-#define PASS_1_DIS_BIT_BEG 8
-#define PASS_1_DIS_BIT_END 13
+// Return the beginning bit for the last FS pass.
+static inline int getLastFSPassBitBegin() {
+  return getFSPassBitBegin(getNumFSPasses());
+}
 
-#define PASS_2_DIS_BIT_BEG 14
-#define PASS_2_DIS_BIT_END 19
+// Return the ending bit for the last FS pass.
+static inline unsigned getLastFSPassBitEnd() {
+  return getFSPassBitEnd(getNumFSPasses());
+}
 
-#define PASS_3_DIS_BIT_BEG 20
-#define PASS_3_DIS_BIT_END 25
+// Return the beginning bit for the base (first) FS pass.
+static inline unsigned getBaseFSBitBegin() { return 0; }
 
-#define PASS_LAST_DIS_BIT_BEG 26
-#define PASS_LAST_DIS_BIT_END 31
+// Return the ending bit for the base (first) FS pass.
+static inline unsigned getBaseFSBitEnd() {
+  return BaseDiscriminatorBitWidth - 1;
+}
 
-// Set bits range [0 .. n] to 1. Used in FS Discriminators.
+// Set bits in range of [0 .. n] to 1. Used in FS Discriminators.
 static inline unsigned getN1Bits(int N) {
-  if (N >= 31)
+  // Work around the g++ bug that folding "(1U << (N + 1)) - 1" to 0.
+  if (N == 31)
     return 0xFFFFFFFF;
-  return (1 << (N + 1)) - 1;
+  assert((N < 32) && "N is invalid");
+  return (1U << (N + 1)) - 1;
 }
 
 #endif /* LLVM_SUPPORT_DISCRIMINATOR_H */
Index: llvm/lib/CodeGen/MIRFSDiscriminator.cpp
===================================================================
--- llvm/lib/CodeGen/MIRFSDiscriminator.cpp
+++ llvm/lib/CodeGen/MIRFSDiscriminator.cpp
@@ -33,9 +33,8 @@
 
 char &llvm::MIRAddFSDiscriminatorsID = MIRAddFSDiscriminators::ID;
 
-FunctionPass *llvm::createMIRAddFSDiscriminatorsPass(unsigned LowBit,
-                                                     unsigned HighBit) {
-  return new MIRAddFSDiscriminators(LowBit, HighBit);
+FunctionPass *llvm::createMIRAddFSDiscriminatorsPass(unsigned PassNum) {
+  return new MIRAddFSDiscriminators(PassNum);
 }
 
 // Compute a hash value using debug line number, and the line numbers from the
Index: llvm/lib/CodeGen/TargetPassConfig.cpp
===================================================================
--- llvm/lib/CodeGen/TargetPassConfig.cpp
+++ llvm/lib/CodeGen/TargetPassConfig.cpp
@@ -1178,8 +1178,11 @@
   addPass(&PatchableFunctionID);
 
   if (EnableFSDiscriminator && !FSNoFinalDiscrim)
-    addPass(createMIRAddFSDiscriminatorsPass(PASS_LAST_DIS_BIT_BEG,
-                                             PASS_LAST_DIS_BIT_END));
+    // Add FS discriminators here so that all the instruction duplicates
+    // in different BBs get their own discriminators. With this, we can "sum"
+    // the SampleFDO counters instead of using MAX. This will improve the
+    // SampleFDO profile quality.
+    addPass(createMIRAddFSDiscriminatorsPass(getNumFSPasses()));
 
   addPreEmitPass();
 
Index: llvm/lib/ProfileData/SampleProf.cpp
===================================================================
--- llvm/lib/ProfileData/SampleProf.cpp
+++ llvm/lib/ProfileData/SampleProf.cpp
@@ -42,6 +42,7 @@
 bool FunctionSamples::ProfileIsCS = false;
 bool FunctionSamples::UseMD5 = false;
 bool FunctionSamples::HasUniqSuffix = true;
+bool FunctionSamples::ProfileIsFS = false;
 } // namespace sampleprof
 } // namespace llvm
 
@@ -232,9 +233,15 @@
 
   const DILocation *PrevDIL = DIL;
   for (DIL = DIL->getInlinedAt(); DIL; DIL = DIL->getInlinedAt()) {
-    S.push_back(std::make_pair(
-        LineLocation(getOffset(DIL), DIL->getBaseDiscriminator()),
-        PrevDIL->getScope()->getSubprogram()->getLinkageName()));
+    unsigned Discriminator;
+    if (ProfileIsFS)
+      Discriminator = DIL->getDiscriminator();
+    else
+      Discriminator = DIL->getBaseDiscriminator();
+
+    S.push_back(
+        std::make_pair(LineLocation(getOffset(DIL), Discriminator),
+                       PrevDIL->getScope()->getSubprogram()->getLinkageName()));
     PrevDIL = DIL;
   }
   if (S.size() == 0)
Index: llvm/lib/ProfileData/SampleProfReader.cpp
===================================================================
--- llvm/lib/ProfileData/SampleProfReader.cpp
+++ llvm/lib/ProfileData/SampleProfReader.cpp
@@ -26,6 +26,7 @@
 #include "llvm/IR/ProfileSummary.h"
 #include "llvm/ProfileData/ProfileCommon.h"
 #include "llvm/ProfileData/SampleProf.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Compression.h"
 #include "llvm/Support/ErrorOr.h"
 #include "llvm/Support/LEB128.h"
@@ -45,6 +46,15 @@
 using namespace llvm;
 using namespace sampleprof;
 
+#define DEBUG_TYPE "samplepgo-reader"
+
+// This internal option specifies if the profile uses FS discriminators.
+// It only applies to text, binary and compact binary format profiles.
+// For ext-binary format profiles, the flag is set in the summary.
+static cl::opt<bool> ProfileIsFSDisciminator(
+    "profile-isfs", cl::Hidden, cl::init(false),
+    cl::desc("Profile uses flow senstive discriminators"));
+
 /// Dump the function profile for \p FName.
 ///
 /// \param FName Name of the function to print.
@@ -238,6 +248,7 @@
   // top-level function profile.
   bool SeenMetadata = false;
 
+  ProfileIsFS = ProfileIsFSDisciminator;
   for (; !LineIt.is_at_eof(); ++LineIt) {
     if ((*LineIt)[(*LineIt).find_first_not_of(' ')] == '#')
       continue;
@@ -295,6 +306,10 @@
                     "Found non-metadata after metadata: " + *LineIt);
         return sampleprof_error::malformed;
       }
+
+      // Here we handle FS discriminators.
+      Discriminator &= getDiscriminatorMask();
+
       while (InlineStack.size() > Depth) {
         InlineStack.pop_back();
       }
@@ -504,6 +519,9 @@
     if (std::error_code EC = NumCalls.getError())
       return EC;
 
+    // Here we handle FS discriminators:
+    uint32_t DiscriminatorVal = (*Discriminator) & getDiscriminatorMask();
+
     for (uint32_t J = 0; J < *NumCalls; ++J) {
       auto CalledFunction(readStringFromTable());
       if (std::error_code EC = CalledFunction.getError())
@@ -513,11 +531,11 @@
       if (std::error_code EC = CalledFunctionSamples.getError())
         return EC;
 
-      FProfile.addCalledTargetSamples(*LineOffset, *Discriminator,
+      FProfile.addCalledTargetSamples(*LineOffset, DiscriminatorVal,
                                       *CalledFunction, *CalledFunctionSamples);
     }
 
-    FProfile.addBodySamples(*LineOffset, *Discriminator, *NumSamples);
+    FProfile.addBodySamples(*LineOffset, DiscriminatorVal, *NumSamples);
   }
 
   // Read all the samples for inlined function calls.
@@ -538,8 +556,11 @@
     if (std::error_code EC = FName.getError())
       return EC;
 
+    // Here we handle FS discriminators:
+    uint32_t DiscriminatorVal = (*Discriminator) & getDiscriminatorMask();
+
     FunctionSamples &CalleeProfile = FProfile.functionSamplesAt(
-        LineLocation(*LineOffset, *Discriminator))[std::string(*FName)];
+        LineLocation(*LineOffset, DiscriminatorVal))[std::string(*FName)];
     CalleeProfile.setName(*FName);
     if (std::error_code EC = readProfile(CalleeProfile))
       return EC;
@@ -575,6 +596,7 @@
 }
 
 std::error_code SampleProfileReaderBinary::readImpl() {
+  ProfileIsFS = ProfileIsFSDisciminator;
   while (!at_eof()) {
     if (std::error_code EC = readFuncProfile(Data))
       return EC;
@@ -595,6 +617,8 @@
       Summary->setPartialProfile(true);
     if (hasSecFlag(Entry, SecProfSummaryFlags::SecFlagFullContext))
       FunctionSamples::ProfileIsCS = ProfileIsCS = true;
+    if (hasSecFlag(Entry, SecProfSummaryFlags::SecFlagFSDiscriminator))
+      FunctionSamples::ProfileIsFS = ProfileIsFS = true;
     break;
   case SecNameTable: {
     FixedLengthMD5 =
@@ -860,7 +884,7 @@
   // Collect functions used by current module if the Reader has been
   // given a module.
   bool LoadFuncsToBeUsed = collectFuncsFromModule();
-
+  ProfileIsFS = ProfileIsFSDisciminator;
   std::vector<uint64_t> OffsetsToUse;
   if (!LoadFuncsToBeUsed) {
     // load all the function profiles.
@@ -1105,6 +1129,8 @@
       Flags.append("partial,");
     if (hasSecFlag(Entry, SecProfSummaryFlags::SecFlagFullContext))
       Flags.append("context,");
+    if (hasSecFlag(Entry, SecProfSummaryFlags::SecFlagFSDiscriminator))
+      Flags.append("fs-discriminator,");
     break;
   default:
     break;
@@ -1521,6 +1547,7 @@
 /// This format is generated by the Linux Perf conversion tool at
 /// https://github.com/google/autofdo.
 std::error_code SampleProfileReaderGCC::readImpl() {
+  assert(!ProfileIsFSDisciminator && "Gcc profiles not support FSDisciminator");
   // Read the string table.
   if (std::error_code EC = readNameTable())
     return EC;
Index: llvm/lib/ProfileData/SampleProfWriter.cpp
===================================================================
--- llvm/lib/ProfileData/SampleProfWriter.cpp
+++ llvm/lib/ProfileData/SampleProfWriter.cpp
@@ -252,6 +252,8 @@
     addSectionFlag(SecProfSummary, SecProfSummaryFlags::SecFlagFullContext);
   if (Type == SecFuncMetadata && FunctionSamples::ProfileIsCS)
     addSectionFlag(SecFuncMetadata, SecFuncMetadataFlags::SecFlagHasAttribute);
+  if (Type == SecProfSummary && FunctionSamples::ProfileIsFS)
+    addSectionFlag(SecProfSummary, SecProfSummaryFlags::SecFlagFSDiscriminator);
 
   uint64_t SectionStart = markSectionStart(Type, LayoutIdx);
   switch (Type) {
Index: llvm/lib/Target/X86/X86InsertPrefetch.cpp
===================================================================
--- llvm/lib/Target/X86/X86InsertPrefetch.cpp
+++ llvm/lib/Target/X86/X86InsertPrefetch.cpp
@@ -167,6 +167,7 @@
     return false;
   }
   Reader = std::move(ReaderOrErr.get());
+  Reader->setDiscriminatorMaskedBitFrom(0);
   Reader->read();
   return true;
 }
Index: llvm/lib/Transforms/IPO/SampleProfile.cpp
===================================================================
--- llvm/lib/Transforms/IPO/SampleProfile.cpp
+++ llvm/lib/Transforms/IPO/SampleProfile.cpp
@@ -1769,6 +1769,7 @@
   // set module before reading the profile so reader may be able to only
   // read the function profiles which are used by the current module.
   Reader->setModule(&M);
+  Reader->setDiscriminatorMaskedBitFrom(0);
   if (std::error_code EC = Reader->read()) {
     std::string Msg = "profile reading failed: " + EC.message();
     Ctx.diagnose(DiagnosticInfoSampleProfile(Filename, Msg));
Index: llvm/test/Transforms/SampleProfile/Inputs/fsafdo.prof
===================================================================
--- /dev/null
+++ llvm/test/Transforms/SampleProfile/Inputs/fsafdo.prof
@@ -0,0 +1,35 @@
+work:33383580:1068858
+ 1: 981870
+ 5: 981870
+foo:22388581:3449
+ 0: 3449
+ 2.1: 204820
+ 4: 213086 bar:205247
+ 4.2013265920: 222893 bar:218378
+ 4.2281701376: 214552 bar:217479
+ 4.2550136832: 210692 bar:220056
+ 5: 213086
+ 5.1207959552: 210692
+ 5.1610612736: 202301
+ 5.2952790016: 222893
+ 6: 4780
+ 6.268435456: 202301 work:198259
+ 6.1073741824: 222893 work:231680
+ 6.2147483648: 4780
+ 7: 219065
+ 7.134217728: 217053
+ 7.2013265920: 183304
+ 7.3758096384: 222101
+ 8: 4780
+ 8.2818572288: 222101 work:238765
+ 8.3489660928: 183304 work:181615
+ 8.4160749568: 217053 work:218539
+ 10: 3281
+bar:7622325:861160
+ 2: 846925
+ 3: 846925
+main:16419:0
+ 0: 0
+ 2.1: 3280
+ 3: 3299 foo:3449
+ 5: 0
Index: llvm/test/Transforms/SampleProfile/fsafdo_test.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/SampleProfile/fsafdo_test.ll
@@ -0,0 +1,230 @@
+; RUN: opt < %s -sample-profile -sample-profile-file=%S/Inputs/fsafdo.extbinary.afdo | opt -analyze -branch-prob -enable-new-pm=0 | FileCheck %s
+; RUN: opt < %s -sample-profile -profile-isfs -sample-profile-file=%S/Inputs/fsafdo.prof | opt -analyze -branch-prob -enable-new-pm=0 | FileCheck %s
+
+target triple = "x86_64-unknown-linux-gnu"
+
+@sum = dso_local local_unnamed_addr global i32 0, align 4
+
+declare i32 @bar(i32 %i) #0
+declare void @work(i32 %i) #2
+
+define dso_local void @foo() #0 !dbg !29 {
+; CHECK: Printing analysis {{.*}} for function 'foo':
+
+entry:
+  br label %for.cond1.preheader, !dbg !30
+; CHECK: edge entry -> for.cond1.preheader probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
+
+for.cond1.preheader:
+  %j.012 = phi i32 [ 0, %entry ], [ %inc11, %if.end9.3 ]
+  %mul = mul nuw nsw i32 %j.012, 48
+  %call = tail call i32 @bar(i32 %mul), !dbg !32
+  %0 = and i32 %call, 1, !dbg !33
+  %tobool.not = icmp eq i32 %0, 0, !dbg !33
+  br i1 %tobool.not, label %if.end, label %if.then, !dbg !35
+; CHECK: edge for.cond1.preheader -> if.end probability is 0x3f6262b8 / 0x80000000 = 49.52%
+; CHECK: edge for.cond1.preheader -> if.then probability is 0x409d9d48 / 0x80000000 = 50.48%
+
+
+if.then:
+  %mul4 = shl nsw i32 %call, 1, !dbg !36
+  tail call void @work(i32 %mul4), !dbg !37
+  br label %if.end, !dbg !38
+; CHECK: edge if.then -> if.end probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
+
+if.end:
+  %1 = and i32 %call, 3, !dbg !39
+  %tobool6.not = icmp eq i32 %1, 0, !dbg !39
+  br i1 %tobool6.not, label %if.end9, label %if.then7, !dbg !40
+; CHECK: edge if.end -> if.end9 probability is 0x22c6bac3 / 0x80000000 = 27.17%
+; CHECK: edge if.end -> if.then7 probability is 0x5d39453d / 0x80000000 = 72.83%
+
+
+if.then7:
+  %mul8 = mul nsw i32 %call, 3, !dbg !41
+  tail call void @work(i32 %mul8), !dbg !42
+  br label %if.end9, !dbg !43
+; CHECK: edge if.then7 -> if.end9 probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
+
+if.end9:
+  %add.1 = or i32 %mul, 1, !dbg !44
+  %call.1 = tail call i32 @bar(i32 %add.1), !dbg !32
+  %2 = and i32 %call.1, 1, !dbg !33
+  %tobool.not.1 = icmp eq i32 %2, 0, !dbg !33
+  br i1 %tobool.not.1, label %if.end.1, label %if.then.1, !dbg !35
+; CHECK: edge if.end9 -> if.end.1 probability is 0x3f6262b8 / 0x80000000 = 49.52%
+; CHECK: edge if.end9 -> if.then.1 probability is 0x409d9d48 / 0x80000000 = 50.48%
+
+for.end12:
+  ret void, !dbg !45
+
+if.then.1:
+  %mul4.1 = shl nsw i32 %call.1, 1, !dbg !36
+  tail call void @work(i32 %mul4.1), !dbg !37
+  br label %if.end.1, !dbg !38
+; CHECK: edge if.then.1 -> if.end.1 probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
+
+if.end.1:
+  %3 = and i32 %call.1, 3, !dbg !39
+  %tobool6.not.1 = icmp eq i32 %3, 0, !dbg !39
+  br i1 %tobool6.not.1, label %if.end9.1, label %if.then7.1, !dbg !40
+; CHECK: edge if.end.1 -> if.end9.1 probability is 0x22c6bac3 / 0x80000000 = 27.17%
+; CHECK: edge if.end.1 -> if.then7.1 probability is 0x5d39453d / 0x80000000 = 72.83%
+
+if.then7.1:
+  %mul8.1 = mul nsw i32 %call.1, 3, !dbg !41
+  tail call void @work(i32 %mul8.1), !dbg !42
+  br label %if.end9.1, !dbg !43
+; CHECK: edge if.then7.1 -> if.end9.1 probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
+
+if.end9.1:
+  %add.2 = or i32 %mul, 2, !dbg !44
+  %call.2 = tail call i32 @bar(i32 %add.2), !dbg !32
+  %4 = and i32 %call.2, 1, !dbg !33
+  %tobool.not.2 = icmp eq i32 %4, 0, !dbg !33
+  br i1 %tobool.not.2, label %if.end.2, label %if.then.2, !dbg !35
+; CHECK: edge if.end9.1 -> if.end.2 probability is 0x3f6262b8 / 0x80000000 = 49.52%
+; CHECK: edge if.end9.1 -> if.then.2 probability is 0x409d9d48 / 0x80000000 = 50.48%
+
+if.then.2:
+  %mul4.2 = shl nsw i32 %call.2, 1, !dbg !36
+  tail call void @work(i32 %mul4.2), !dbg !37
+  br label %if.end.2, !dbg !38
+; CHECK: edge if.then.2 -> if.end.2 probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
+
+if.end.2:
+  %5 = and i32 %call.2, 3, !dbg !39
+  %tobool6.not.2 = icmp eq i32 %5, 0, !dbg !39
+  br i1 %tobool6.not.2, label %if.end9.2, label %if.then7.2, !dbg !40
+; CHECK: edge if.end.2 -> if.end9.2 probability is 0x22c6bac3 / 0x80000000 = 27.17%
+; CHECK: edge if.end.2 -> if.then7.2 probability is 0x5d39453d / 0x80000000 = 72.83%
+
+if.then7.2:
+  %mul8.2 = mul nsw i32 %call.2, 3, !dbg !41
+  tail call void @work(i32 %mul8.2), !dbg !42
+  br label %if.end9.2, !dbg !43
+; CHECK: edge if.then7.2 -> if.end9.2 probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
+
+if.end9.2:
+  %add.3 = or i32 %mul, 3, !dbg !44
+  %call.3 = tail call i32 @bar(i32 %add.3), !dbg !32
+  %6 = and i32 %call.3, 1, !dbg !33
+  %tobool.not.3 = icmp eq i32 %6, 0, !dbg !33
+  br i1 %tobool.not.3, label %if.end.3, label %if.then.3, !dbg !35
+; CHECK: edge if.end9.2 -> if.end.3 probability is 0x3f6262b8 / 0x80000000 = 49.52%
+; CHECK: edge if.end9.2 -> if.then.3 probability is 0x409d9d48 / 0x80000000 = 50.48%
+
+if.then.3:
+  %mul4.3 = shl nsw i32 %call.3, 1, !dbg !36
+  tail call void @work(i32 %mul4.3), !dbg !37
+  br label %if.end.3, !dbg !38
+; CHECK: edge if.then.3 -> if.end.3 probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
+
+if.end.3:
+  %7 = and i32 %call.3, 3, !dbg !39
+  %tobool6.not.3 = icmp eq i32 %7, 0, !dbg !39
+  br i1 %tobool6.not.3, label %if.end9.3, label %if.then7.3, !dbg !40
+; CHECK: edge if.end.3 -> if.end9.3 probability is 0x22c6bac3 / 0x80000000 = 27.17%
+; CHECK: edge if.end.3 -> if.then7.3 probability is 0x5d39453d / 0x80000000 = 72.83%
+
+if.then7.3:
+  %mul8.3 = mul nsw i32 %call.3, 3, !dbg !41
+  tail call void @work(i32 %mul8.3), !dbg !42
+  br label %if.end9.3, !dbg !43
+; CHECK: edge if.then7.3 -> if.end9.3 probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
+
+if.end9.3:
+  %inc11 = add nuw nsw i32 %j.012, 1, !dbg !46
+  %exitcond.not = icmp eq i32 %inc11, 48, !dbg !48
+  br i1 %exitcond.not, label %for.end12, label %for.cond1.preheader, !dbg !30, !llvm.loop !49
+; CHECK: edge if.end9.3 -> for.end12 probability is 0x00834dd9 / 0x80000000 = 0.40%
+; CHECK: edge if.end9.3 -> for.cond1.preheader probability is 0x7f7cb227 / 0x80000000 = 99.60% [HOT edge]
+}
+
+define dso_local i32 @main() #3 !dbg !52 {
+entry:
+  br label %for.body, !dbg !53
+
+for.body:
+  %i.03 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
+  tail call void @foo(), !dbg !55
+  %inc = add nuw nsw i32 %i.03, 1, !dbg !56
+  %exitcond.not = icmp eq i32 %inc, 10000000, !dbg !58
+  br i1 %exitcond.not, label %for.end, label %for.body, !dbg !53, !llvm.loop !60
+
+for.end:
+  ret i32 0, !dbg !63
+}
+
+
+attributes #0 = { noinline nounwind uwtable "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" "unsafe-fp-math"="false" "use-soft-float"="false" "use-sample-profile"}
+attributes #1 = { argmemonly nounwind willreturn }
+attributes #2 = { nofree noinline norecurse nounwind uwtable "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #3 = { nounwind uwtable "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" "unsafe-fp-math"="false" "use-soft-float"="false" }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, isOptimized: true, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2, splitDebugInlining: false, debugInfoForProfiling: true, nameTableKind: None)
+!1 = !DIFile(filename: "unroll.c", directory: "a/")
+!2 = !{}
+!3 = !{i32 7, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!7 = distinct !DISubprogram(name: "bar", scope: !1, file: !1, line: 3, type: !8, scopeLine: 3, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!8 = !DISubroutineType(types: !2)
+!9 = !DILocation(line: 4, column: 3, scope: !7)
+!10 = !DILocation(line: 5, column: 5, scope: !7)
+!11 = !{!12, !12, i64 0}
+!12 = !{!"int", !13, i64 0}
+!13 = !{!"omnipotent char", !14, i64 0}
+!14 = !{!"Simple C/C++ TBAA"}
+!15 = !DILocation(line: 6, column: 10, scope: !7)
+!16 = !DILocation(line: 7, column: 1, scope: !7)
+!17 = !DILocation(line: 6, column: 3, scope: !18)
+!18 = !DILexicalBlockFile(scope: !7, file: !1, discriminator: 1)
+!19 = distinct !DISubprogram(name: "work", scope: !1, file: !1, line: 10, type: !8, scopeLine: 10, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!20 = !DILocation(line: 11, column: 7, scope: !19)
+!21 = !DILocation(line: 11, column: 11, scope: !22)
+!22 = !DILexicalBlockFile(scope: !19, file: !1, discriminator: 1)
+!23 = !DILocation(line: 11, column: 11, scope: !24)
+!24 = !DILexicalBlockFile(scope: !19, file: !1, discriminator: 2)
+!25 = !DILocation(line: 11, column: 7, scope: !26)
+!26 = !DILexicalBlockFile(scope: !19, file: !1, discriminator: 3)
+!27 = !DILocation(line: 0, scope: !22)
+!28 = !DILocation(line: 15, column: 1, scope: !19)
+!29 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 17, type: !8, scopeLine: 17, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!30 = !DILocation(line: 19, column: 3, scope: !31)
+!31 = !DILexicalBlockFile(scope: !29, file: !1, discriminator: 2)
+!32 = !DILocation(line: 21, column: 16, scope: !31)
+!33 = !DILocation(line: 22, column: 14, scope: !34)
+!34 = !DILexicalBlockFile(scope: !29, file: !1, discriminator: 1)
+!35 = !DILocation(line: 22, column: 11, scope: !31)
+!36 = !DILocation(line: 23, column: 16, scope: !29)
+!37 = !DILocation(line: 23, column: 9, scope: !34)
+!38 = !DILocation(line: 23, column: 9, scope: !31)
+!39 = !DILocation(line: 24, column: 14, scope: !34)
+!40 = !DILocation(line: 24, column: 11, scope: !31)
+!41 = !DILocation(line: 25, column: 16, scope: !29)
+!42 = !DILocation(line: 25, column: 9, scope: !34)
+!43 = !DILocation(line: 25, column: 9, scope: !31)
+!44 = !DILocation(line: 21, column: 21, scope: !34)
+!45 = !DILocation(line: 27, column: 1, scope: !29)
+!46 = !DILocation(line: 19, column: 24, scope: !47)
+!47 = !DILexicalBlockFile(scope: !29, file: !1, discriminator: 3)
+!48 = !DILocation(line: 19, column: 17, scope: !34)
+!49 = distinct !{!49, !50, !51}
+!50 = !DILocation(line: 19, column: 3, scope: !29)
+!51 = !DILocation(line: 26, column: 3, scope: !29)
+!52 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 29, type: !8, scopeLine: 29, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!53 = !DILocation(line: 31, column: 3, scope: !54)
+!54 = !DILexicalBlockFile(scope: !52, file: !1, discriminator: 2)
+!55 = !DILocation(line: 32, column: 5, scope: !52)
+!56 = !DILocation(line: 31, column: 30, scope: !57)
+!57 = !DILexicalBlockFile(scope: !52, file: !1, discriminator: 3)
+!58 = !DILocation(line: 31, column: 17, scope: !59)
+!59 = !DILexicalBlockFile(scope: !52, file: !1, discriminator: 1)
+!60 = distinct !{!60, !61, !62}
+!61 = !DILocation(line: 31, column: 3, scope: !52)
+!62 = !DILocation(line: 33, column: 3, scope: !52)
+!63 = !DILocation(line: 34, column: 1, scope: !52)
Index: llvm/unittests/ProfileData/SampleProfTest.cpp
===================================================================
--- llvm/unittests/ProfileData/SampleProfTest.cpp
+++ llvm/unittests/ProfileData/SampleProfTest.cpp
@@ -9,6 +9,7 @@
 #include "llvm/ProfileData/SampleProf.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Metadata.h"
 #include "llvm/IR/Module.h"
@@ -61,6 +62,7 @@
     ASSERT_TRUE(NoError(ReaderOrErr.getError()));
     Reader = std::move(ReaderOrErr.get());
     Reader->setModule(&M);
+    Reader->setDiscriminatorMaskedBitFrom(0);
   }
 
   TempFile createRemapFile() {