[ELF] - Use multithreading for building .gdb_index.

[grimar]

Summary

Looks it is can be enabled now.

[ruiu]

ELF/SyntheticSections.cpp

1816

InfoSections -> Sections.

1819

No need to change the original code.

ObjFile<ELFT> *F = Sections[I]->getFile<ELFT>();
DWARFContext Dwarf(make_unique<LLDDwarfObj<ELFT>>(F));
Chunks[I] = readDwarf(Dwarf, Sections[I]);

[grimar]

• Addressed comments.

[ruiu]

LGTM

ELF/SyntheticSections.cpp

static GdbIndexChunk readDwarf(DWARFContext &Dwarf, InputSection *Sec) {
   Ret.DebugInfoSec = Sec;
   Ret.CompilationUnits = readCuList(Dwarf);
   Ret.AddressArea = readAddressArea(Dwarf, Sec);
   Ret.NamesAndTypes = readPubNamesAndTypes(Dwarf, Config->IsLE);
   return Ret;
 }
 
 template <class ELFT> GdbIndexSection *elf::createGdbIndex() {
-  std::vector<GdbIndexChunk> Chunks;
-  for (InputSection *Sec : getDebugInfoSections()) {
-    ObjFile<ELFT> *F = Sec->getFile<ELFT>();
-    DWARFContext Dwarf(make_unique<LLDDwarfObj<ELFT>>(F));
-    Chunks.push_back(readDwarf(Dwarf, Sec));
-  }
+  std::vector<InputSection *> InfoSections = getDebugInfoSections();
+  std::vector<GdbIndexChunk> Chunks(InfoSections.size());
+  parallelForEachN(0, Chunks.size(), [&](size_t I) {
+    InputSection *Sec = InfoSections[I];
+    DWARFContext Dwarf(make_unique<LLDDwarfObj<ELFT>>(Sec->getFile<ELFT>()));
+    Chunks[I] = readDwarf(Dwarf, Sec);
+  });
   return make<GdbIndexSection>(std::move(Chunks));
 }
 
 static size_t getCuSize(std::vector<GdbIndexChunk> &C) {
   size_t Ret = 0;
   for (GdbIndexChunk &D : C)
     Ret += D.CompilationUnits.size();
   return Ret;