[lld] Reject --read-workers when lld is built without thread support

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"))
@@ -390,6 +389,7 @@ static void multiThreadedPageIn(const DeferredFiles &deferred) {
     multiThreadedPageInBackground(files);
   });
 }
+#endif
 
 static InputFile *processFile(std::optional<MemoryBufferRef> buffer,
                               DeferredFiles *archiveContents, StringRef path,
@@ -1430,6 +1430,7 @@ static void createFiles(const InputArgList &args) {
     }
   }
 
+#if LLVM_ENABLE_THREADS
   if (config->readWorkers) {
     multiThreadedPageIn(deferredFiles);
 
@@ -1447,6 +1448,7 @@ static void createFiles(const InputArgList &args) {
     for (auto *archive : archives)
       archive->addLazySymbols();
   }
+#endif
 }
 
 static void gatherInputSections() {
@@ -1834,13 +1836,18 @@ 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))
       error(arg->getSpelling() +
             ": expected a non-negative integer, but got '" + arg->getValue() +
             "'");
     config->readWorkers = workers;
+#else
+    error(arg->getSpelling() +
+          ": option unavailable because lld was not built with thread support");
+#endif
   }
   if (auto *arg = args.getLastArg(OPT_threads_eq)) {
     StringRef v(arg->getValue());

lld/test/CMakeLists.txt

@@ -1,5 +1,6 @@
 llvm_canonicalize_cmake_booleans(
   ENABLE_BACKTRACES
+  LLVM_ENABLE_THREADS
   LLVM_ENABLE_ZLIB
   LLVM_ENABLE_ZSTD
   LLVM_ENABLE_LIBXML2

lld/test/MachO/read-workers-no-thread-support.s

@@ -0,0 +1,10 @@
+# REQUIRES: x86 && !thread_support
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
+
+# RUN: not %lld --read-workers=1 %t.o -o /dev/null
+
+# CHECK: error: --read-workers=: option unavailable because lld was built without thread support
+
+.globl _main
+_main:
+  ret

lld/test/MachO/read-workers.s

@@ -1,4 +1,4 @@
-# REQUIRES: x86
+# REQUIRES: x86 && thread_support
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
 
 ## A non-negative integer is allowed.

lld/test/lit.cfg.py

@@ -182,3 +182,6 @@
 # ELF tests expect the default target for ld.lld to be ELF.
 if config.ld_lld_default_mingw:
     config.excludes.append("ELF")
+
+if config.enable_threads:
+    config.available_features.add("thread_support")

lld/test/lit.site.cfg.py.in

@@ -26,6 +26,7 @@ config.ld_lld_default_mingw = @LLD_DEFAULT_LD_LLD_IS_MINGW@
 config.build_examples = @LLVM_BUILD_EXAMPLES@
 config.has_plugins = @LLVM_ENABLE_PLUGINS@
 config.linked_bye_extension = @LLVM_BYE_LINK_INTO_TOOLS@
+config.enable_threads = @LLVM_ENABLE_THREADS@
 
 import lit.llvm
 lit.llvm.initialize(lit_config, config)