[lld-macho][nfc] Remove indirection when looking up common section members

[int3]

Summary

D118797: [lld-macho][nfc] Eliminate InputSection::Shared means that we can now check the name/segname of a given
section directly, instead of having to look those properties up on one
of its subsections. This allows us to simplify our code.

[int3]

This one should be fairly easy to review :)

[oontvoo]

LG

[int3]

Thanks!

lld/MachO/Driver.cpp

static void createFiles(const InputArgList &args) {
   }
 }
 
 static void gatherInputSections() {
   TimeTraceScope timeScope("Gathering input sections");
   int inputOrder = 0;
   for (const InputFile *file : inputFiles) {
     for (const Section *section : file->sections) {
-      const Subsections &subsections = section->subsections;
-      if (subsections.empty())
-        continue;
-      if (subsections[0].isec->getName() == section_names::compactUnwind)
+      if (section->name == section_names::compactUnwind)
         // Compact unwind entries require special handling elsewhere.
         continue;
       ConcatOutputSection *osec = nullptr;
-      for (const Subsection &subsection : subsections) {
+      for (const Subsection &subsection : section->subsections) {
         if (auto *isec = dyn_cast<ConcatInputSection>(subsection.isec)) {
           if (isec->isCoalescedWeak())
             continue;
           isec->outSecOff = inputOrder++;
           if (!osec)
             osec = ConcatOutputSection::getOrCreateForInput(isec);
           isec->parent = osec;
           inputSections.push_back(isec);

lld/MachO/InputFiles.h

 std::vector<const CommandType *> findCommands(const void *anyHdr,
                                               Types... types) {
   return detail::findCommands<CommandType>(anyHdr, 0, types...);
 }
 
 } // namespace macho
 
 std::string toString(const macho::InputFile *file);
+std::string toString(const macho::Section &);
 } // namespace lld
 
 #endif

lld/MachO/InputFiles.cpp

if (auto dylibFile = dyn_cast<DylibFile>(f))
     if (f->getName().endswith(".tbd"))
       return (f->getName() + "(" + dylibFile->installName + ")").str();
 
   if (f->archiveName.empty())
     return std::string(f->getName());
   return (f->archiveName + "(" + path::filename(f->getName()) + ")").str();
 }
 
+std::string lld::toString(const Section &sec) {
+  return (toString(sec.file) + ":(" + sec.name + ")").str();
+}
+
 SetVector<InputFile *> macho::inputFiles;
 std::unique_ptr<TarWriter> macho::tar;
 int InputFile::idCount = 0;
 
 static VersionTuple decodeVersion(uint32_t version) {
   unsigned major = version >> 16;
   unsigned minor = (version >> 8) & 0xffu;
   unsigned subMinor = version & 0xffu;
for (const SectionHeader &sec : sectionHeaders) {
     StringRef segname =
         StringRef(sec.segname, strnlen(sec.segname, sizeof(sec.segname)));
     sections.push_back(make<Section>(this, segname, name, sec.flags, sec.addr));
     if (sec.align >= 32) {
       error("alignment " + std::to_string(sec.align) + " of section " + name +
             " is too large");
       continue;
     }
-    const Section &section = *sections.back();
+    Section &section = *sections.back();
     uint32_t align = 1 << sec.align;
     ArrayRef<uint8_t> data = {isZeroFill(sec.flags) ? nullptr
                                                     : buf + sec.offset,
                               static_cast<size_t>(sec.size)};
 
     auto splitRecords = [&](int recordSize) -> void {
       if (data.empty())
         return;
-      Subsections &subsections = sections.back()->subsections;
+      Subsections &subsections = section.subsections;
       subsections.reserve(data.size() / recordSize);
       for (uint64_t off = 0; off < data.size(); off += recordSize) {
         auto *isec = make<ConcatInputSection>(
             section, data.slice(off, recordSize), align);
         subsections.push_back({off, isec});
       }
     };
 
     if (sectionType(sec.flags) == S_CSTRING_LITERALS ||
         (config->dedupLiterals && isWordLiteralSection(sec.flags))) {
       if (sec.nreloc && config->dedupLiterals)
         fatal(toString(this) + " contains relocations in " + sec.segname + "," +
               sec.sectname +
               ", so LLD cannot deduplicate literals. Try re-running without "
               "--deduplicate-literals.");
 
       InputSection *isec;
       if (sectionType(sec.flags) == S_CSTRING_LITERALS) {
         isec = make<CStringInputSection>(section, data, align);
         // FIXME: parallelize this?
         cast<CStringInputSection>(isec)->splitIntoPieces();
       } else {
         isec = make<WordLiteralInputSection>(section, data, align);
       }
-      sections.back()->subsections.push_back({0, isec});
+      section.subsections.push_back({0, isec});
     } else if (auto recordSize = getRecordSize(segname, name)) {
       splitRecords(*recordSize);
       if (name == section_names::compactUnwind)
-        compactUnwindSection = sections.back();
+        compactUnwindSection = &section;
     } else if (segname == segment_names::llvm) {
       if (config->callGraphProfileSort && name == section_names::cgProfile)
         checkError(parseCallGraph(data, callGraph));
       // ld64 does not appear to emit contents from sections within the __LLVM
       // segment. Symbols within those sections point to bitcode metadata
       // instead of actual symbols. Global symbols within those sections could
       // have the same name without causing duplicate symbol errors. To avoid
       // spurious duplicate symbol errors, we do not parse these sections.
       // TODO: Evaluate whether the bitcode metadata is needed.
     } else {
       auto *isec = make<ConcatInputSection>(section, data, align);
       if (isDebugSection(isec->getFlags()) &&
           isec->getSegName() == segment_names::dwarf) {
         // Instead of emitting DWARF sections, we emit STABS symbols to the
         // object files that contain them. We filter them out early to avoid
         // parsing their relocations unnecessarily.
         debugSections.push_back(isec);
       } else {
-        sections.back()->subsections.push_back({0, isec});
+        section.subsections.push_back({0, isec});
       }
     }
   }
 }
 
 // Find the subsection corresponding to the greatest section offset that is <=
 // that of the given offset.
 //
if ((sym.n_type & N_TYPE) == N_SECT) {
       symbols[i] = parseNonSectionSymbol(sym, name);
     }
   }
 
   for (size_t i = 0; i < sections.size(); ++i) {
     Subsections &subsections = sections[i]->subsections;
     if (subsections.empty())
       continue;
-    InputSection *lastIsec = subsections.back().isec;
-    if (lastIsec->getName() == section_names::ehFrame) {
+    if (sections[i]->name == section_names::ehFrame) {
       // __TEXT,__eh_frame only has symbols and SUBTRACTOR relocs when ld64 -r
       // adds local "EH_Frame1" and "func.eh". Ignore them because they have
       // gone unused by Mac OS since Snow Leopard (10.6), vintage 2009.
       continue;
     }
     std::vector<uint32_t> &symbolIndices = symbolsBySection[i];
     uint64_t sectionAddr = sectionHeaders[i].addr;
     uint32_t sectionAlign = 1u << sectionHeaders[i].align;
 
     // Record-based sections have already been split into subsections during
     // parseSections(), so we simply need to match Symbols to the corresponding
     // subsection here.
-    if (getRecordSize(lastIsec->getSegName(), lastIsec->getName())) {
+    if (getRecordSize(sections[i]->segname, sections[i]->name)) {
       for (size_t j = 0; j < symbolIndices.size(); ++j) {
         uint32_t symIndex = symbolIndices[j];
         const NList &sym = nList[symIndex];
         StringRef name = strtab + sym.n_strx;
         uint64_t symbolOffset = sym.n_value - sectionAddr;
         InputSection *isec =
             findContainingSubsection(*sections[i], &symbolOffset);
         if (symbolOffset != 0) {
-          error(toString(lastIsec) + ":  symbol " + name +
+          error(toString(*sections[i]) + ":  symbol " + name +
                 " at misaligned offset");
           continue;
         }
         symbols[symIndex] = createDefined(sym, name, isec, 0, isec->getSize());
       }
       continue;
     }