[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.

1 files changed, 10 insertions, 6 deletions

diff --git a/llvm/lib/ProfileData/SampleProf.cpp b/llvm/lib/ProfileData/SampleProf.cpp
index 0c47df3..60c1393 100644
--- a/llvm/lib/ProfileData/SampleProf.cpp
+++ b/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);