[lld] [lld][MachO]Multi-threaded i/o. Twice as fast linking a large project. (PR #147134)

[John Holdsworth via llvm-commits]

johnno1962 wrote:

Thanks for stepping in @DavidSpickett, You can certain broaden the scope of the '#if LLVM_ENABLE_THREADS':
```
diff --git a/lld/MachO/Driver.cpp b/lld/MachO/Driver.cpp
index 7ce987e400a2..7ed19ba7e346 100644
--- a/lld/MachO/Driver.cpp
+++ b/lld/MachO/Driver.cpp
@@ -291,6 +291,7 @@ struct DeferredFile {
 };
 using DeferredFiles = std::vector<DeferredFile>;
 
+#if LLVM_ENABLE_THREADS
 class SerialBackgroundQueue {
   std::deque<std::function<void()>> queue;
   std::thread *running;
@@ -359,7 +360,6 @@ void multiThreadedPageInBackground(DeferredFiles &deferred) {
       (void)t;
     }
   };
-#if LLVM_ENABLE_THREADS
   { // Create scope for waiting for the taskGroup
     std::atomic_size_t index = 0;
     llvm::parallel::TaskGroup taskGroup;
@@ -373,7 +373,6 @@ void multiThreadedPageInBackground(DeferredFiles &deferred) {
         }
       });
   }
-#endif
 #ifndef NDEBUG
   auto dt = high_resolution_clock::now() - t0;
   if (Process::GetEnv("LLD_MULTI_THREAD_PAGE"))
@@ -382,13 +381,16 @@ void multiThreadedPageInBackground(DeferredFiles &deferred) {
                  << duration_cast<milliseconds>(dt).count() / 1000. << "\n";
 #endif
 }
+#endif
 
 static void multiThreadedPageIn(const DeferredFiles &deferred) {
+  #if LLVM_ENABLE_THREADS
   static SerialBackgroundQueue pageInQueue;
   pageInQueue.queueWork([=]() {
     DeferredFiles files = deferred;
     multiThreadedPageInBackground(files);
   });
+  #endif
 }
 
 static InputFile *processFile(std::optional<MemoryBufferRef> buffer,
@@ -1834,6 +1836,7 @@ bool link(ArrayRef<const char *> argsArr, llvm::raw_ostream &stdoutOS,
   }
 
   if (auto *arg = args.getLastArg(OPT_read_workers)) {
+    #if LLVM_ENABLE_THREADS
     StringRef v(arg->getValue());
     unsigned workers = 0;
     if (!llvm::to_integer(v, workers, 0))
@@ -1841,6 +1844,10 @@ bool link(ArrayRef<const char *> argsArr, llvm::raw_ostream &stdoutOS,
             ": expected a non-negative integer, but got '" + arg->getValue() +
             "'");
     config->readWorkers = workers;
+    #else
+    error(arg->getSpelling() +
+          ": option unavailable");
+    #endif
   }
   if (auto *arg = args.getLastArg(OPT_threads_eq)) {
     StringRef v(arg->getValue());
```
This should get things up and running again while I look into trying to replicate what the issue is.

https://github.com/llvm/llvm-project/pull/147134