[NFC]Codestyle changes for SampleFDO library (#147840)

* Introduce an error code for illegal_line_offset in sampleprof_error
namespace, and use it for line offset parsing error.
* Add `const` for `LineLocation::serialize`.
* Use structured binding, make_first/second_range in loops.

I'm working on a [sample-profile format
change](https://github.com/llvm/llvm-project/compare/users/mingmingl-llvm/samplefdo-profile-format)
to extend SampleFDO profile with vtable profiles. And this change splits
the non-functional changes.

Author: mingmingl-llvm

llvm/include/llvm/ProfileData/SampleProf.h

@@ -61,7 +61,8 @@ enum class sampleprof_error {
   ostream_seek_unsupported,
   uncompress_failed,
   zlib_unavailable,
-  hash_mismatch
+  hash_mismatch,
+  illegal_line_offset
 };
 
 inline std::error_code make_error_code(sampleprof_error E) {
@@ -286,7 +287,7 @@ struct LineLocation {
   LLVM_ABI void dump() const;
 
   // Serialize the line location to the output stream using ULEB128 encoding.
-  LLVM_ABI void serialize(raw_ostream &OS);
+  LLVM_ABI void serialize(raw_ostream &OS) const;
 
   bool operator<(const LineLocation &O) const {
     return std::tie(LineOffset, Discriminator) <

llvm/lib/ProfileData/SampleProf.cpp

@@ -91,6 +91,8 @@ class SampleProfErrorCategoryType : public std::error_category {
       return "Zlib is unavailable";
     case sampleprof_error::hash_mismatch:
       return "Function hash mismatch";
+    case sampleprof_error::illegal_line_offset:
+      return "Illegal line offset in sample profile data";
     }
     llvm_unreachable("A value of sampleprof_error has no message.");
   }
@@ -150,7 +152,7 @@ std::error_code SampleRecord::serialize(
 LLVM_DUMP_METHOD void LineLocation::dump() const { print(dbgs()); }
 #endif
 
-void LineLocation::serialize(raw_ostream &OS) {
+void LineLocation::serialize(raw_ostream &OS) const {
   encodeULEB128(LineOffset, OS);
   encodeULEB128(Discriminator, OS);
 }
@@ -203,12 +205,14 @@ void FunctionSamples::print(raw_ostream &OS, unsigned Indent) const {
     OS << "Samples collected in inlined callsites {\n";
     SampleSorter<LineLocation, FunctionSamplesMap> SortedCallsiteSamples(
         CallsiteSamples);
-    for (const auto &CS : SortedCallsiteSamples.get()) {
-      for (const auto &FS : CS->second) {
+    for (const auto *Element : SortedCallsiteSamples.get()) {
+      // Element is a pointer to a pair of LineLocation and FunctionSamplesMap.
+      const auto &[Loc, FunctionSampleMap] = *Element;
+      for (const FunctionSamples &FuncSample :
+           llvm::make_second_range(FunctionSampleMap)) {
         OS.indent(Indent + 2);
-        OS << CS->first << ": inlined callee: " << FS.second.getFunction()
-           << ": ";
-        FS.second.print(OS, Indent + 4);
+        OS << Loc << ": inlined callee: " << FuncSample.getFunction() << ": ";
+        FuncSample.print(OS, Indent + 4);
       }
     }
     OS.indent(Indent);

llvm/lib/ProfileData/SampleProfReader.cpp

@@ -609,7 +609,7 @@ SampleProfileReaderBinary::readProfile(FunctionSamples &FProfile) {
       return EC;
 
     if (!isOffsetLegal(*LineOffset)) {
-      return std::error_code();
+      return sampleprof_error::illegal_line_offset;
     }
 
     auto Discriminator = readNumber<uint64_t>();
@@ -1236,7 +1236,7 @@ std::error_code SampleProfileReaderExtBinaryBase::readCSNameTableSec() {
         return EC;
 
       if (!isOffsetLegal(*LineOffset))
-        return std::error_code();
+        return sampleprof_error::illegal_line_offset;
 
       auto Discriminator = readNumber<uint64_t>();
       if (std::error_code EC = Discriminator.getError())

llvm/lib/ProfileData/SampleProfWriter.cpp

@@ -592,16 +592,18 @@ std::error_code SampleProfileWriterText::writeSample(const FunctionSamples &S) {
   SampleSorter<LineLocation, FunctionSamplesMap> SortedCallsiteSamples(
       S.getCallsiteSamples());
   Indent += 1;
-  for (const auto &I : SortedCallsiteSamples.get())
-    for (const auto &FS : I->second) {
-      LineLocation Loc = I->first;
-      const FunctionSamples &CalleeSamples = FS.second;
+  for (const auto *Element : SortedCallsiteSamples.get()) {
+    // Element is a pointer to a pair of LineLocation and FunctionSamplesMap.
+    const auto &[Loc, FunctionSamplesMap] = *Element;
+    for (const FunctionSamples &CalleeSamples :
+         make_second_range(FunctionSamplesMap)) {
       OS.indent(Indent);
       Loc.print(OS);
       OS << ": ";
       if (std::error_code EC = writeSample(CalleeSamples))
         return EC;
     }
+  }
   Indent -= 1;
 
   if (FunctionSamples::ProfileIsProbeBased) {
@@ -836,12 +838,11 @@ std::error_code SampleProfileWriterBinary::writeBody(const FunctionSamples &S) {
   for (const auto &J : S.getCallsiteSamples())
     NumCallsites += J.second.size();
   encodeULEB128(NumCallsites, OS);
-  for (const auto &J : S.getCallsiteSamples())
-    for (const auto &FS : J.second) {
-      LineLocation Loc = J.first;
-      const FunctionSamples &CalleeSamples = FS.second;
+  for (const auto &[Loc, CalleeFunctionSampleMap] : S.getCallsiteSamples())
+    for (const auto &FunctionSample :
+         llvm::make_second_range(CalleeFunctionSampleMap)) {
       Loc.serialize(OS);
-      if (std::error_code EC = writeBody(CalleeSamples))
+      if (std::error_code EC = writeBody(FunctionSample))
         return EC;
     }