[lld-macho][NFC] when reasonable, replace auto keyword with type names

lld policy discourages `auto`. Replace it with a type name whenever reasonable. Retain `auto` to avoid ...
* redundancy, as for decls such as `auto *t = mumble_cast<TYPE *>` or similar that specifies the result type on the RHS
* verbosity, as for iterators
* gratuitous suffering, as for lambdas

Along the way, add `const` when appropriate.

Note: a future diff will ...
* add more `const` qualifiers
* remove `opt::` when we are already `using llvm::opt`

Differential Revision: https://reviews.llvm.org/D98313

lld/MachO/Driver.cpp

@@ -164,8 +164,8 @@ getSearchPaths(unsigned optionCode, opt::InputArgList &args,
   if (args.hasArg(OPT_Z))
     return paths;
 
-  for (auto const &path : systemPaths) {
+  for (const StringRef &path : systemPaths) {
-    for (auto root : roots) {
+    for (const StringRef &root : roots) {
       SmallString<261> buffer(root);
       path::append(buffer, path);
       if (fs::is_directory(buffer))
@@ -252,7 +252,7 @@ static InputFile *addFile(StringRef path, bool forceLoadArchive,
   MemoryBufferRef mbref = *buffer;
   InputFile *newFile = nullptr;
 
-  auto magic = identify_magic(mbref.getBuffer());
+  file_magic magic = identify_magic(mbref.getBuffer());
   switch (magic) {
   case file_magic::archive: {
     std::unique_ptr<object::Archive> file = CHECK(
@@ -368,10 +368,10 @@ void macho::parseLCLinkerOption(InputFile* f, unsigned argc, StringRef data) {
   opt::InputArgList args = table.ParseArgs(argv, missingIndex, missingCount);
   if (missingCount)
     fatal(Twine(args.getArgString(missingIndex)) + ": missing argument");
-  for (auto *arg : args.filtered(OPT_UNKNOWN))
+  for (const Arg *arg : args.filtered(OPT_UNKNOWN))
     error("unknown argument: " + arg->getAsString(args));
 
-  for (auto *arg : args) {
+  for (const Arg *arg : args) {
     switch (arg->getOption().getID()) {
     case OPT_l:
       addLibrary(arg->getValue(), false);
@@ -493,7 +493,7 @@ static void initLLVM() {
 }
 
 static void compileBitcodeFiles() {
-  auto lto = make<BitcodeCompiler>();
+  auto *lto = make<BitcodeCompiler>();
   for (InputFile *file : inputFiles)
     if (auto *bitcodeFile = dyn_cast<BitcodeFile>(file))
       lto->add(*bitcodeFile);
@@ -663,7 +663,7 @@ static void warnIfUnimplementedOption(const opt::Option &opt) {
 }
 
 static const char *getReproduceOption(opt::InputArgList &args) {
-  if (auto *arg = args.getLastArg(OPT_reproduce))
+  if (const Arg *arg = args.getLastArg(OPT_reproduce))
     return arg->getValue();
   return getenv("LLD_REPRODUCE");
 }
@@ -752,9 +752,9 @@ static void handleSymbolPatterns(opt::InputArgList &args,
                                  SymbolPatterns &symbolPatterns,
                                  unsigned singleOptionCode,
                                  unsigned listFileOptionCode) {
-  for (opt::Arg *arg : args.filtered(singleOptionCode))
+  for (const Arg *arg : args.filtered(singleOptionCode))
     symbolPatterns.insert(arg->getValue());
-  for (opt::Arg *arg : args.filtered(listFileOptionCode)) {
+  for (const Arg *arg : args.filtered(listFileOptionCode)) {
     StringRef path = arg->getValue();
     Optional<MemoryBufferRef> buffer = readFile(path);
     if (!buffer) {
@@ -819,12 +819,12 @@ bool macho::link(ArrayRef<const char *> argsArr, bool canExitEarly,
   config->entry = symtab->addUndefined(args.getLastArgValue(OPT_e, "_main"),
                                        /*file=*/nullptr,
                                        /*isWeakRef=*/false);
-  for (auto *arg : args.filtered(OPT_u)) {
+  for (const Arg *arg : args.filtered(OPT_u)) {
     config->explicitUndefineds.push_back(symtab->addUndefined(
         arg->getValue(), /*file=*/nullptr, /*isWeakRef=*/false));
   }
 
-  for (auto *arg : args.filtered(OPT_U))
+  for (const Arg *arg : args.filtered(OPT_U))
     symtab->addDynamicLookup(arg->getValue());
 
   config->outputFile = args.getLastArgValue(OPT_o, "a.out");
@@ -884,12 +884,12 @@ bool macho::link(ArrayRef<const char *> argsArr, bool canExitEarly,
       error("invalid name for segment or section: " + s);
     return s;
   };
-  for (opt::Arg *arg : args.filtered(OPT_rename_section)) {
+  for (const Arg *arg : args.filtered(OPT_rename_section)) {
     config->sectionRenameMap[{validName(arg->getValue(0)),
                               validName(arg->getValue(1))}] = {
         validName(arg->getValue(2)), validName(arg->getValue(3))};
   }
-  for (opt::Arg *arg : args.filtered(OPT_rename_segment)) {
+  for (const Arg *arg : args.filtered(OPT_rename_segment)) {
     config->segmentRenameMap[validName(arg->getValue(0))] =
         validName(arg->getValue(1));
   }
@@ -926,8 +926,8 @@ bool macho::link(ArrayRef<const char *> argsArr, bool canExitEarly,
 
   // This loop should be reserved for options whose exact ordering matters.
   // Other options should be handled via filtered() and/or getLastArg().
-  for (const auto &arg : args) {
+  for (const Arg *arg : args) {
-    const auto &opt = arg->getOption();
+    const Option &opt = arg->getOption();
     warnIfDeprecatedOption(opt);
     warnIfUnimplementedOption(opt);
 
@@ -964,7 +964,7 @@ bool macho::link(ArrayRef<const char *> argsArr, bool canExitEarly,
 
   // Now that all dylibs have been loaded, search for those that should be
   // re-exported.
-  for (opt::Arg *arg : args.filtered(OPT_sub_library, OPT_sub_umbrella)) {
+  for (const Arg *arg : args.filtered(OPT_sub_library, OPT_sub_umbrella)) {
     config->hasReexports = true;
     StringRef searchName = arg->getValue();
     std::vector<StringRef> extensions;
@@ -978,11 +978,11 @@ bool macho::link(ArrayRef<const char *> argsArr, bool canExitEarly,
   }
 
   // Parse LTO options.
-  if (auto *arg = args.getLastArg(OPT_mcpu))
+  if (const Arg *arg = args.getLastArg(OPT_mcpu))
     parseClangOption(saver.save("-mcpu=" + StringRef(arg->getValue())),
                      arg->getSpelling());
 
-  for (auto *arg : args.filtered(OPT_mllvm))
+  for (const Arg *arg : args.filtered(OPT_mllvm))
     parseClangOption(arg->getValue(), arg->getSpelling());
 
   compileBitcodeFiles();
@@ -998,7 +998,7 @@ bool macho::link(ArrayRef<const char *> argsArr, bool canExitEarly,
   }
   // FIXME: This prints symbols that are undefined both in input files and
   // via -u flag twice.
-  for (const auto *undefined : config->explicitUndefineds) {
+  for (const Symbol *undefined : config->explicitUndefineds) {
     if (isa<Undefined>(undefined)) {
       error("undefined symbol: " + toString(*undefined) +
             "\n>>> referenced by flag -u " + toString(*undefined));
@@ -1009,7 +1009,7 @@ bool macho::link(ArrayRef<const char *> argsArr, bool canExitEarly,
   createSyntheticSections();
   symtab->addDSOHandle(in.header);
 
-  for (opt::Arg *arg : args.filtered(OPT_sectcreate)) {
+  for (const Arg *arg : args.filtered(OPT_sectcreate)) {
     StringRef segName = arg->getValue(0);
     StringRef sectName = arg->getValue(1);
     StringRef fileName = arg->getValue(2);
@@ -1021,7 +1021,7 @@ bool macho::link(ArrayRef<const char *> argsArr, bool canExitEarly,
   // Initialize InputSections.
   for (InputFile *file : inputFiles) {
     for (SubsectionMap &map : file->subsections) {
-      for (auto &p : map) {
+      for (const auto &p : map) {
         InputSection *isec = p.second;
         inputSections.push_back(isec);
       }

lld/MachO/DriverUtils.cpp

@@ -52,8 +52,9 @@ MachOOptTable::MachOOptTable() : OptTable(optInfo) {}
 // Set color diagnostics according to --color-diagnostics={auto,always,never}
 // or --no-color-diagnostics flags.
 static void handleColorDiagnostics(opt::InputArgList &args) {
-  auto *arg = args.getLastArg(OPT_color_diagnostics, OPT_color_diagnostics_eq,
+  const Arg *arg =
-                              OPT_no_color_diagnostics);
+      args.getLastArg(OPT_color_diagnostics, OPT_color_diagnostics_eq,
+                      OPT_no_color_diagnostics);
   if (!arg)
     return;
   if (arg->getOption().getID() == OPT_color_diagnostics) {
@@ -121,7 +122,7 @@ std::string macho::createResponseFile(const opt::InputArgList &args) {
   raw_svector_ostream os(data);
 
   // Copy the command line to the output while rewriting paths.
-  for (auto *arg : args) {
+  for (const Arg *arg : args) {
     switch (arg->getOption().getID()) {
     case OPT_reproduce:
       break;

lld/MachO/InputFiles.cpp

@@ -99,8 +99,8 @@ int InputFile::idCount = 0;
 // Open a given file path and return it as a memory-mapped file.
 Optional<MemoryBufferRef> macho::readFile(StringRef path) {
   // Open a file.
-  auto mbOrErr = MemoryBuffer::getFile(path);
+  ErrorOr<std::unique_ptr<MemoryBuffer>> mbOrErr = MemoryBuffer::getFile(path);
-  if (auto ec = mbOrErr.getError()) {
+  if (std::error_code ec = mbOrErr.getError()) {
     error("cannot open " + path + ": " + ec.message());
     return None;
   }
@@ -749,7 +749,7 @@ DylibFile::DylibFile(const InterfaceFile &interface, DylibFile *umbrella,
   };
   // TODO(compnerd) filter out symbols based on the target platform
   // TODO: handle weak defs, thread locals
-  for (const auto symbol : interface.symbols()) {
+  for (const auto *symbol : interface.symbols()) {
     if (!symbol->getArchitectures().has(config->target.Arch))
       continue;
 
@@ -776,7 +776,7 @@ DylibFile::DylibFile(const InterfaceFile &interface, DylibFile *umbrella,
       interface.getParent() == nullptr ? &interface : interface.getParent();
 
   for (InterfaceFileRef intfRef : interface.reexportedLibraries()) {
-    auto targets = intfRef.targets();
+    InterfaceFile::const_target_range targets = intfRef.targets();
     if (is_contained(targets, config->target))
       loadReexport(intfRef.getInstallName(), exportingFile, topLevel);
   }

lld/MachO/InputSection.cpp

@@ -58,14 +58,15 @@ void InputSection::writeTo(uint8_t *buf) {
   memcpy(buf, data.data(), data.size());
 
   for (size_t i = 0; i < relocs.size(); i++) {
-    auto *fromSym = target->hasAttr(relocs[i].type, RelocAttrBits::SUBTRAHEND)
+    const Symbol *fromSym =
-                        ? relocs[i++].referent.get<Symbol *>()
+        target->hasAttr(relocs[i].type, RelocAttrBits::SUBTRAHEND)
-                        : nullptr;
+            ? relocs[i++].referent.get<Symbol *>()
+            : nullptr;
     const Reloc &r = relocs[i];
     uint8_t *loc = buf + r.offset;
     uint64_t referentVA = 0;
     if (fromSym) {
-      auto *toSym = r.referent.get<Symbol *>();
+      const Symbol *toSym = r.referent.get<Symbol *>();
       referentVA = toSym->getVA() - fromSym->getVA();
     } else if (auto *referentSym = r.referent.dyn_cast<Symbol *>()) {
       if (target->hasAttr(r.type, RelocAttrBits::LOAD) &&

lld/MachO/LTO.cpp

@@ -40,7 +40,7 @@ static lto::Config createConfig() {
 }
 
 BitcodeCompiler::BitcodeCompiler() {
-  auto backend =
+  lto::ThinBackend backend =
       lto::createInProcessThinBackend(heavyweight_hardware_concurrency());
   ltoObj = std::make_unique<lto::LTO>(createConfig(), backend);
 }

lld/MachO/SymbolTable.cpp

@@ -79,7 +79,7 @@ Symbol *SymbolTable::addUndefined(StringRef name, InputFile *file,
   bool wasInserted;
   std::tie(s, wasInserted) = insert(name);
 
-  auto refState = isWeakRef ? RefState::Weak : RefState::Strong;
+  RefState refState = isWeakRef ? RefState::Weak : RefState::Strong;
 
   if (wasInserted)
     replaceSymbol<Undefined>(s, name, file, refState);
@@ -119,7 +119,7 @@ Symbol *SymbolTable::addDylib(StringRef name, DylibFile *file, bool isWeakDef,
   bool wasInserted;
   std::tie(s, wasInserted) = insert(name);
 
-  auto refState = RefState::Unreferenced;
+  RefState refState = RefState::Unreferenced;
   if (!wasInserted) {
     if (auto *defined = dyn_cast<Defined>(s)) {
       if (isWeakDef && !defined->isWeakDef())

lld/MachO/SyntheticSections.cpp

@@ -372,11 +372,11 @@ void WeakBindingSection::finalizeContents() {
                return a.target.getVA() < b.target.getVA();
              });
   for (const WeakBindingEntry &b : bindings) {
-    if (auto *isec = b.target.section.dyn_cast<const InputSection *>()) {
+    if (const auto *isec = b.target.section.dyn_cast<const InputSection *>()) {
       encodeBinding(b.symbol, isec->parent, isec->outSecOff + b.target.offset,
                     b.addend, /*isWeakBinding=*/true, lastBinding, os);
     } else {
-      auto *osec = b.target.section.get<const OutputSection *>();
+      const auto *osec = b.target.section.get<const OutputSection *>();
       encodeBinding(b.symbol, osec, b.target.offset, b.addend,
                     /*isWeakBinding=*/true, lastBinding, os);
     }

lld/MachO/UnwindInfoSection.cpp

@@ -280,7 +280,7 @@ void UnwindInfoSection::finalize() {
 
   // Count frequencies of the folded encodings
   EncodingMap encodingFrequencies;
-  for (auto cuPtrEntry : cuPtrVector)
+  for (const CompactUnwindEntry64 *cuPtrEntry : cuPtrVector)
     encodingFrequencies[cuPtrEntry->encoding]++;
 
   // Make a vector of encodings, sorted by descending frequency
@@ -316,7 +316,7 @@ void UnwindInfoSection::finalize() {
   // If more entries fit in the regular format, we use that.
   for (size_t i = 0; i < cuPtrVector.size();) {
     secondLevelPages.emplace_back();
-    auto &page = secondLevelPages.back();
+    UnwindInfoSection::SecondLevelPage &page = secondLevelPages.back();
     page.entryIndex = i;
     uintptr_t functionAddressMax =
         cuPtrVector[i]->functionAddress + COMPRESSED_ENTRY_FUNC_OFFSET_MASK;
@@ -326,7 +326,7 @@ void UnwindInfoSection::finalize() {
         sizeof(unwind_info_compressed_second_level_page_header) /
             sizeof(uint32_t);
     while (wordsRemaining >= 1 && i < cuPtrVector.size()) {
-      const auto *cuPtr = cuPtrVector[i];
+      const CompactUnwindEntry64 *cuPtr = cuPtrVector[i];
       if (cuPtr->functionAddress >= functionAddressMax) {
         break;
       } else if (commonEncodingIndexes.count(cuPtr->encoding) ||