[ObjectYAML][DWARF] Remove unused context. NFC.

[Higuoxing]

Summary

The context is unused. This patch helps remove it.

[jhenderson]

Are you sure it's unused? I took a quick look and the function void MappingTraits<DWARFYAML::PubEntry>::mapping uses it to determine the style (GNU/non-GNU).

[Higuoxing]

In D82351#2108345, @jhenderson wrote:

Are you sure it's unused? I took a quick look and the function void MappingTraits<DWARFYAML::PubEntry>::mapping uses it to determine the style (GNU/non-GNU).

Yeah, the GNU-style is determined by DWARFYAML::PubSection rather than DWARFYAML::Data. The DWARF context is never used.

void MappingTraits<DWARFYAML::PubEntry>::mapping(IO &IO,
                                                 DWARFYAML::PubEntry &Entry) {
  IO.mapRequired("DieOffset", Entry.DieOffset);
  if (reinterpret_cast<DWARFYAML::PubSection *>(IO.getContext())->IsGNUStyle)
                                                ^---------------------------+
    IO.mapRequired("Descriptor", Entry.Descriptor);                         |
  IO.mapRequired("Name", Entry.Name);                                       |
}                                                                           |
                                                                            |
void MappingTraits<DWARFYAML::PubSection>::mapping(                         |
    IO &IO, DWARFYAML::PubSection &Section) {                               |
  auto OldContext = IO.getContext();   // unused                            |
  IO.setContext(&Section);                                                  |
  ^-------------------------------------------------------------------------+
  IO.mapRequired("Length", Section.Length);
  IO.mapRequired("Version", Section.Version);
  IO.mapRequired("UnitOffset", Section.UnitOffset);
  IO.mapRequired("UnitSize", Section.UnitSize);
  IO.mapRequired("Entries", Section.Entries);

  IO.setContext(OldContext);
}

Besides, the implementation of mapping YAML to PubSection is buggy. If we map debug_gnu_pubnames/debug_gnu_pubtypes to PubSection, the GNUStyle is always false and Descriptor can never be mapped into Entry.Descriptor.
In other words, if we have

DWARF:
  debug_gnu_pubtypes:
    Length:
      TotalLength: 0x1234
    Version:    2
    UnitOffset: 0x1234
    UnitSize:   0x4321
    Entries:
      - DieOffset: 0x12345678
        Name:      abc
        Descriptor: 0x00      ## Descripor can never be mapped into Entry.Descriptor

yaml2obj will complain that error: unknown key 'Descriptor'.

But if we map PubSection to debug_gnu_pubnames/debug_gnu_pubtypes, that is fine since the GNUStyle has been set by obj2yaml.

I'm wondering if we need to add support for emitting the .debug_gnu_pubnames and .debug_gnu_pubtypes since no test case relies on them.

[jhenderson]

Thanks, I see. LGTM. I can't comment on the .debug_gnu_pub* stuff, but I wouldn't bother adding support for it at this point. It can be added/fixed later if you have time, but other aspects are probably of greater priority. It might be a good idea to file some kind of bug though.

[Higuoxing]

In D82351#2108469, @jhenderson wrote:

It might be a good idea to file some kind of bug though.

Thanks, I'll do it later. It seems that Bugzilla isn't working right now. I've reported it to the list.

llvm/lib/ObjectYAML/DWARFYAML.cpp

SetVector<StringRef> DWARFYAML::Data::getUsedSectionNames() const {
   if (!CompileUnits.empty())
     SecNames.insert("debug_info");
   return SecNames;
 }
 
 namespace yaml {
 
 void MappingTraits<DWARFYAML::Data>::mapping(IO &IO, DWARFYAML::Data &DWARF) {
-  auto oldContext = IO.getContext();
-  IO.setContext(&DWARF);
   IO.mapOptional("debug_str", DWARF.DebugStrings);
   IO.mapOptional("debug_abbrev", DWARF.AbbrevDecls);
   if (!DWARF.ARanges.empty() || !IO.outputting())
     IO.mapOptional("debug_aranges", DWARF.ARanges);
   if (!DWARF.DebugRanges.empty() || !IO.outputting())
     IO.mapOptional("debug_ranges", DWARF.DebugRanges);
   IO.mapOptional("debug_pubnames", DWARF.PubNames);
   IO.mapOptional("debug_pubtypes", DWARF.PubTypes);
   IO.mapOptional("debug_gnu_pubnames", DWARF.GNUPubNames);
   IO.mapOptional("debug_gnu_pubtypes", DWARF.GNUPubTypes);
   IO.mapOptional("debug_info", DWARF.CompileUnits);
   IO.mapOptional("debug_line", DWARF.DebugLines);
   IO.mapOptional("debug_addr", DWARF.DebugAddr);
-  IO.setContext(&oldContext);
 }
 
 void MappingTraits<DWARFYAML::Abbrev>::mapping(IO &IO,
                                                DWARFYAML::Abbrev &Abbrev) {
   IO.mapOptional("Code", Abbrev.Code);
   IO.mapRequired("Tag", Abbrev.Tag);
   IO.mapRequired("Children", Abbrev.Children);
   IO.mapRequired("Attributes", Abbrev.Attributes);