[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, 9 deletions

diff --git a/llvm/lib/ProfileData/SampleProfWriter.cpp b/llvm/lib/ProfileData/SampleProfWriter.cpp
index 71d2f52..9173a0f 100644
--- a/llvm/lib/ProfileData/SampleProfWriter.cpp
+++ b/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;
     }