Index: llvm/trunk/tools/dsymutil/DwarfLinker.cpp
===================================================================
--- llvm/trunk/tools/dsymutil/DwarfLinker.cpp
+++ llvm/trunk/tools/dsymutil/DwarfLinker.cpp
@@ -4301,8 +4301,6 @@
   if (MaxDwarfVersion == 0)
     MaxDwarfVersion = 3;
 
-  ThreadPool pool(2);
-
   // These variables manage the list of processed object files.
   // The mutex and condition variable are to ensure that this is thread safe.
   std::mutex ProcessedFilesMutex;
@@ -4310,7 +4308,7 @@
   BitVector ProcessedFiles(NumObjects, false);
 
   // Now do analyzeContextInfo in parallel as it is particularly expensive.
-  pool.async([&]() {
+  auto AnalyzeLambda = [&]() {
     for (unsigned i = 0, e = NumObjects; i != e; ++i) {
       auto &LinkContext = ObjectContexts[i];
 
@@ -4331,13 +4329,13 @@
       ProcessedFiles.set(i);
       ProcessedFilesConditionVariable.notify_one();
     }
-  });
+  };
 
   // And then the remaining work in serial again.
   // Note, although this loop runs in serial, it can run in parallel with
   // the analyzeContextInfo loop so long as we process files with indices >=
   // than those processed by analyzeContextInfo.
-  pool.async([&]() {
+  auto CloneLambda = [&]() {
     for (unsigned i = 0, e = NumObjects; i != e; ++i) {
       {
         std::unique_lock<std::mutex> LockGuard(ProcessedFilesMutex);
@@ -4397,9 +4395,20 @@
       Streamer->emitAppleTypes(AppleTypes);
       Streamer->emitAppleObjc(AppleObjc);
     }
-  });
+  };
 
-  pool.wait();
+  // FIXME: The DwarfLinker can have some very deep recursion that can max
+  // out the (significantly smaller) stack when using threads. We don't
+  // want this limitation when we only have a single thread.
+  if (Options.Threads == 1) {
+    AnalyzeLambda();
+    CloneLambda();
+  } else {
+    ThreadPool pool(2);
+    pool.async(AnalyzeLambda);
+    pool.async(CloneLambda);
+    pool.wait();
+  }
 
   return Options.NoOutput ? true : Streamer->finish(Map);
 }
Index: llvm/trunk/tools/dsymutil/dsymutil.h
===================================================================
--- llvm/trunk/tools/dsymutil/dsymutil.h
+++ llvm/trunk/tools/dsymutil/dsymutil.h
@@ -48,6 +48,9 @@
   /// Do not check swiftmodule timestamp
   bool NoTimestamp = false;
 
+  /// Number of threads.
+  unsigned Threads = 1;
+
   /// -oso-prepend-path
   std::string PrependPath;
 
Index: llvm/trunk/tools/dsymutil/dsymutil.cpp
===================================================================
--- llvm/trunk/tools/dsymutil/dsymutil.cpp
+++ llvm/trunk/tools/dsymutil/dsymutil.cpp
@@ -324,6 +324,11 @@
         inconvertibleErrorCode());
   }
 
+  if (NumThreads == 0)
+    Options.Threads = llvm::thread::hardware_concurrency();
+  if (DumpDebugMap || Verbose)
+    Options.Threads = 1;
+
   return Options;
 }
 
@@ -480,12 +485,8 @@
       return 1;
     }
 
-    if (NumThreads == 0)
-      NumThreads = llvm::thread::hardware_concurrency();
-    if (DumpDebugMap || Verbose)
-      NumThreads = 1;
-    NumThreads = std::min<unsigned>(NumThreads, DebugMapPtrsOrErr->size());
-
+    NumThreads =
+        std::min<unsigned>(OptionsOrErr->Threads, DebugMapPtrsOrErr->size());
     llvm::ThreadPool Threads(NumThreads);
 
     // If there is more than one link to execute, we need to generate