[lld-macho][NFC] Refactor syslibroot / library path lookup

[int3]

Summary

• Move computation of systemLibraryRoots into a separate function, so we can add more functionality to it without things becoming unwieldy
• Have getSearchPaths and related functions return by value instead of by output parameter. NRVO should ensure that performance is unaffected.

[smeenai]

LGTM

lld/MachO/Driver.cpp

if (!fs::exists(path)) {
     return false;
   } else if (!fs::is_directory(path)) {
     warn("option -" + option + path + " references a non-directory path");
     return false;
   }
   return true;
 }
 
-static void getSearchPaths(std::vector<StringRef> &paths, unsigned optionCode,
-                           opt::InputArgList &args,
-                           const std::vector<StringRef> &roots,
-                           const SmallVector<StringRef, 2> &systemPaths) {
+static std::vector<StringRef>
+getSearchPaths(unsigned optionCode, opt::InputArgList &args,
+  std::vector<StringRef> paths;
   StringRef optionLetter{optionCode == OPT_F ? "F" : "L"};
   for (StringRef path : args::getStrings(args, optionCode)) {
     // NOTE: only absolute paths are re-rooted to syslibroot(s)
     bool found = false;
     if (path::is_absolute(path, path::Style::posix)) {
       for (StringRef root : roots) {
         SmallString<261> buffer(root);
         path::append(buffer, path);
         // Do not warn about paths that are computed via the syslib roots
         if (fs::is_directory(buffer)) {
           paths.push_back(saver.save(buffer.str()));
           found = true;
         }
       }
     }
     if (!found && warnIfNotDirectory(optionLetter, path))
       paths.push_back(path);
   }
 
   // `-Z` suppresses the standard "system" search paths.
   if (args.hasArg(OPT_Z))
-    return;
+    return paths;
 
   for (auto const &path : systemPaths) {
     for (auto root : roots) {
       SmallString<261> buffer(root);
       path::append(buffer, path);
       if (warnIfNotDirectory(optionLetter, buffer))
         paths.push_back(saver.save(buffer.str()));
     }
   }
+  return paths;
 }
 
-static void getLibrarySearchPaths(opt::InputArgList &args,
-                                  const std::vector<StringRef> &roots,
-                                  std::vector<StringRef> &paths) {
-  getSearchPaths(paths, OPT_L, args, roots, {"/usr/lib", "/usr/local/lib"});
+static std::vector<StringRef> getSystemLibraryRoots(opt::InputArgList &args) {
+  std::vector<StringRef> roots;
+  for (const Arg *arg : args.filtered(OPT_syslibroot))
+    roots.push_back(arg->getValue());
+  // NOTE: the final `-syslibroot` being `/` will ignore all roots
+  if (roots.size() && roots.back() == "/")
+    roots.clear();
+  // NOTE: roots can never be empty - add an empty root to simplify the library
+  // and framework search path computation.
+  if (roots.empty())
+    roots.emplace_back("");
+  return roots;
 }
 
-static void getFrameworkSearchPaths(opt::InputArgList &args,
-                                    const std::vector<StringRef> &roots,
-                                    std::vector<StringRef> &paths) {
-  getSearchPaths(paths, OPT_F, args, roots,
+static std::vector<StringRef>
+getLibrarySearchPaths(opt::InputArgList &args,
+                      const std::vector<StringRef> &roots) {
+  return getSearchPaths(OPT_L, args, roots, {"/usr/lib", "/usr/local/lib"});
+}
+
+static std::vector<StringRef>
+getFrameworkSearchPaths(opt::InputArgList &args,
+                        const std::vector<StringRef> &roots) {
+  return getSearchPaths(OPT_F, args, roots,
                         {"/Library/Frameworks", "/System/Library/Frameworks"});
 }
 
 // Returns slices of MB by parsing MB as an archive file.
 // Each slice consists of a member file in the archive.
 static std::vector<MemoryBufferRef> getArchiveMembers(MemoryBufferRef mb) {
   std::unique_ptr<Archive> file =
       CHECK(Archive::create(mb),
             mb.getBufferIdentifier() + ": failed to parse archive");
bool macho::link(llvm::ArrayRef<const char *> argsArr, bool canExitEarly,
   config->installName =
       args.getLastArgValue(OPT_install_name, config->outputFile);
   config->headerPad = args::getHex(args, OPT_headerpad, /*Default=*/32);
   config->headerPadMaxInstallNames =
       args.hasArg(OPT_headerpad_max_install_names);
   config->outputType = args.hasArg(OPT_dylib) ? MH_DYLIB : MH_EXECUTE;
   config->runtimePaths = args::getStrings(args, OPT_rpath);
   config->allLoad = args.hasArg(OPT_all_load);
+  config->forceLoadObjC = args.hasArg(OPT_ObjC);
 
   if (const opt::Arg *arg = args.getLastArg(OPT_static, OPT_dynamic))
     config->staticLink = (arg->getOption().getID() == OPT_static);
 
-  std::vector<StringRef> &roots = config->systemLibraryRoots;
-  for (const Arg *arg : args.filtered(OPT_syslibroot))
-    roots.push_back(arg->getValue());
-  // NOTE: the final `-syslibroot` being `/` will ignore all roots
-  if (roots.size() && roots.back() == "/")
-    roots.clear();
-  // NOTE: roots can never be empty - add an empty root to simplify the library
-  // and framework search path computation.
-  if (roots.empty())
-    roots.emplace_back("");
-
-  getLibrarySearchPaths(args, roots, config->librarySearchPaths);
-  getFrameworkSearchPaths(args, roots, config->frameworkSearchPaths);
+  config->systemLibraryRoots = getSystemLibraryRoots(args);
+  config->librarySearchPaths =
+      getLibrarySearchPaths(args, config->systemLibraryRoots);
+  config->frameworkSearchPaths =
+      getFrameworkSearchPaths(args, config->systemLibraryRoots);
   if (const opt::Arg *arg =
           args.getLastArg(OPT_search_paths_first, OPT_search_dylibs_first))
     config->searchDylibsFirst =
         (arg && arg->getOption().getID() == OPT_search_dylibs_first);
-  config->forceLoadObjC = args.hasArg(OPT_ObjC);
 
   if (args.hasArg(OPT_v)) {
     message(getLLDVersion());
     message(StringRef("Library search paths:") +
             (config->librarySearchPaths.size()
                  ? "\n\t" + llvm::join(config->librarySearchPaths, "\n\t")
                  : ""));
     message(StringRef("Framework search paths:") +