Sample profiles - Re-arrange binary format to emit head samples only on top functions.

The number of samples collected at the head of a function only make
sense for top-level functions (i.e., those actually called as opposed to
being inlined inside another).

Head samples essentially count the time spent inside the function's
prologue.  This clearly doesn't make sense for inlined functions, so we
were always emitting 0 in those.

llvm-svn: 250539

llvm/include/llvm/ProfileData/SampleProf.h

@@ -61,7 +61,7 @@ static inline uint64_t SPMagic() {
          uint64_t('2') << (64 - 56) | uint64_t(0xff);
 }
 
-static inline uint64_t SPVersion() { return 101; }
+static inline uint64_t SPVersion() { return 102; }
 
 /// Represents the relative location of an instruction.
 ///

llvm/include/llvm/ProfileData/SampleProfReader.h

@@ -136,12 +136,16 @@
 //        A NUL-separated list of SIZE strings.
 //
 // FUNCTION BODY (one for each uninlined function body present in the profile)
+//    HEAD_SAMPLES (uint64_t) [only for top-level functions]
+//        Total number of samples collected at the head (prologue) of the
+//        function.
+//        NOTE: This field should only be present for top-level functions
+//              (i.e., not inlined into any caller). Inlined function calls
+//              have no prologue, so they don't need this.
 //    NAME_IDX (uint32_t)
 //        Index into the name table indicating the function name.
 //    SAMPLES (uint64_t)
 //        Total number of samples collected in this function.
-//    HEAD_SAMPLES (uint64_t)
-//        Total number of samples collected at the head of the function.
 //    NRECS (uint32_t)
 //        Total number of sampling records this function's profile.
 //    BODY RECORDS

llvm/include/llvm/ProfileData/SampleProfWriter.h

@@ -105,6 +105,7 @@ protected:
   std::error_code
   writeHeader(const StringMap<FunctionSamples> &ProfileMap) override;
   std::error_code writeNameIdx(StringRef FName);
+  std::error_code writeBody(StringRef FName, const FunctionSamples &S);
 
 private:
   void addName(StringRef FName);

llvm/lib/ProfileData/SampleProfReader.cpp

@@ -21,13 +21,13 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ProfileData/SampleProfReader.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorOr.h"
 #include "llvm/Support/LEB128.h"
 #include "llvm/Support/LineIterator.h"
 #include "llvm/Support/MemoryBuffer.h"
-#include "llvm/ADT/DenseMap.h"
-#include "llvm/ADT/SmallVector.h"
 
 using namespace llvm::sampleprof;
 using namespace llvm;
@@ -293,15 +293,10 @@ ErrorOr<StringRef> SampleProfileReaderBinary::readStringFromTable() {
 
 std::error_code
 SampleProfileReaderBinary::readProfile(FunctionSamples &FProfile) {
-  auto Val = readNumber<uint64_t>();
-  if (std::error_code EC = Val.getError())
+  auto NumSamples = readNumber<uint64_t>();
+  if (std::error_code EC = NumSamples.getError())
     return EC;
-  FProfile.addTotalSamples(*Val);
-
-  Val = readNumber<uint64_t>();
-  if (std::error_code EC = Val.getError())
-    return EC;
-  FProfile.addHeadSamples(*Val);
+  FProfile.addTotalSamples(*NumSamples);
 
   // Read the samples in the body.
   auto NumRecords = readNumber<uint32_t>();
@@ -370,6 +365,10 @@ SampleProfileReaderBinary::readProfile(FunctionSamples &FProfile) {
 
 std::error_code SampleProfileReaderBinary::read() {
   while (!at_eof()) {
+    auto NumHeadSamples = readNumber<uint64_t>();
+    if (std::error_code EC = NumHeadSamples.getError())
+      return EC;
+
     auto FName(readStringFromTable());
     if (std::error_code EC = FName.getError())
       return EC;
@@ -377,6 +376,8 @@ std::error_code SampleProfileReaderBinary::read() {
     Profiles[*FName] = FunctionSamples();
     FunctionSamples &FProfile = Profiles[*FName];
 
+    FProfile.addHeadSamples(*NumHeadSamples);
+
     if (std::error_code EC = readProfile(FProfile))
       return EC;
   }

llvm/lib/ProfileData/SampleProfWriter.cpp

@@ -122,19 +122,15 @@ std::error_code SampleProfileWriterBinary::writeHeader(
   return sampleprof_error::success;
 }
 
-/// \brief Write samples to a binary file.
-///
-/// \returns true if the samples were written successfully, false otherwise.
-std::error_code SampleProfileWriterBinary::write(StringRef FName,
-                                                 const FunctionSamples &S) {
+std::error_code SampleProfileWriterBinary::writeBody(StringRef FName,
+                                                     const FunctionSamples &S) {
   if (std::error_code EC = writeNameIdx(FName))
     return EC;
 
   encodeULEB128(S.getTotalSamples(), OS);
-  encodeULEB128(S.getHeadSamples(), OS);
-  encodeULEB128(S.getBodySamples().size(), OS);
 
   // Emit all the body samples.
+  encodeULEB128(S.getBodySamples().size(), OS);
   for (const auto &I : S.getBodySamples()) {
     LineLocation Loc = I.first;
     const SampleRecord &Sample = I.second;
@@ -158,13 +154,22 @@ std::error_code SampleProfileWriterBinary::write(StringRef FName,
     const FunctionSamples &CalleeSamples = J.second;
     encodeULEB128(Loc.LineOffset, OS);
     encodeULEB128(Loc.Discriminator, OS);
-    if (std::error_code EC = write(Loc.CalleeName, CalleeSamples))
+    if (std::error_code EC = writeBody(Loc.CalleeName, CalleeSamples))
       return EC;
   }
 
   return sampleprof_error::success;
 }
 
+/// \brief Write samples of a top-level function to a binary file.
+///
+/// \returns true if the samples were written successfully, false otherwise.
+std::error_code SampleProfileWriterBinary::write(StringRef FName,
+                                                 const FunctionSamples &S) {
+  encodeULEB128(S.getHeadSamples(), OS);
+  return writeBody(FName, S);
+}
+
 /// \brief Create a sample profile writer based on the specified format.
 ///
 /// \param Filename The file to create.