[gold-plugin] Disable name for values other than GlobalValue

[tejohnson]

Summary

Applies Mehdi's optimization (r263086) to disable value names other than
for GlobalValues to LTO/ThinLTO performed via the gold-plugin, in the
same manner as it is applied in libLTO.

[• rafael]

Lgtm, but can you add a test?

[tejohnson]

Added test.

tools/gold/gold-plugin.cpp

namespace options {
   static unsigned OptLevel = 2;
   // Default parallelism of 0 used to indicate that user did not specify.
   // Actual parallelism default value depends on implementation.
   // Currently, code generation defaults to no parallelism, whereas
   // ThinLTO uses the hardware_concurrency as the default.
   static unsigned Parallelism = 0;
 #ifdef NDEBUG
   static bool DisableVerify = true;
+  static bool DiscardValueNames = true;
 #else
   static bool DisableVerify = false;
+  static bool DiscardValueNames = false;
 #endif
   static std::string obj_path;
   static std::string extra_library_path;
   static std::string triple;
   static std::string mcpu;
   // When the thinlto plugin option is specified, only read the function
   // the information from intermediate files and write a combined
   // global index for the ThinLTO backends.
if (opt == "generate-api-file") {
       if (opt[1] < '0' || opt[1] > '3')
         message(LDPL_FATAL, "Optimization level must be between 0 and 3");
       OptLevel = opt[1] - '0';
     } else if (opt.startswith("jobs=")) {
       if (StringRef(opt_ + 5).getAsInteger(10, Parallelism))
         message(LDPL_FATAL, "Invalid parallelism level: %s", opt_ + 5);
     } else if (opt == "disable-verify") {
       DisableVerify = true;
+    } else if (opt == "discard-value-names") {
+      DiscardValueNames = true;
     } else {
       // Save this option to pass to the code generator.
       // ParseCommandLineOptions() expects argv[0] to be program name. Lazily
       // add that.
       if (extra.empty())
         extra.push_back("LLVMgold");
 
       extra.push_back(opt_);

 /// pipelines.
 static void thinLTOBackendTask(claimed_file &F, const void *View,
                                ld_plugin_input_file &File,
                                raw_fd_ostream *ApiFile,
                                const ModuleSummaryIndex &CombinedIndex,
                                raw_fd_ostream *OS, unsigned TaskID) {
   // Need to use a separate context for each task
   LLVMContext Context;
+  Context.setDiscardValueNames(options::DiscardValueNames);
   Context.enableDebugTypeODRUniquing(); // Merge debug info types.
   Context.setDiagnosticHandler(diagnosticHandlerForContext, nullptr, true);
 
   std::unique_ptr<llvm::Module> NewModule(new llvm::Module(File.name, Context));
   IRMover L(*NewModule.get());
 
   StringSet<> Dummy;
   if (linkInModule(Context, L, F, View, File, ApiFile, Dummy, Dummy))
if (options::thinlto_index_only) {
       exit(0);
     }
 
     thinLTOBackends(ApiFile, CombinedIndex);
     return LDPS_OK;
   }
 
   LLVMContext Context;
+  Context.setDiscardValueNames(options::DiscardValueNames);
   Context.enableDebugTypeODRUniquing(); // Merge debug info types.
   Context.setDiagnosticHandler(diagnosticHandlerForContext, nullptr, true);
 
   std::unique_ptr<Module> Combined(new Module("ld-temp.o", Context));
   IRMover L(*Combined);
 
   StringSet<> Internalize;
   StringSet<> Maybe;