Index: lldb/unittests/Symbol/TestTypeSystemClang.cpp
===================================================================
--- lldb/unittests/Symbol/TestTypeSystemClang.cpp
+++ lldb/unittests/Symbol/TestTypeSystemClang.cpp
@@ -17,6 +17,9 @@
 #include "clang/AST/DeclObjC.h"
 #include "clang/AST/ExprCXX.h"
 #include "gtest/gtest.h"
+#include "clang/Lex/HeaderSearchOptions.h"
+#include "clang/CodeGen/BackendUtil.h"
+#include "llvm/Support/ThreadPool.h"
 
 using namespace clang;
 using namespace lldb;
@@ -741,3 +744,25 @@
       ScratchTypeSystemClang::IsolatedASTKind::CppModules,
       ScratchTypeSystemClang::InferIsolatedASTKindFromLangOpts(lang_opts));
 }
+
+
+TEST_F(TestTypeSystemClang, FuzzClangBackend) {
+  llvm::ThreadPoolStrategy s;
+  s.ThreadsRequested = 4000;
+  llvm::ThreadPool Pool(s);
+  for (size_t i = 0; i < s.ThreadsRequested; ++i) {
+    Pool.async([this, i] {
+        clang::CodeGenOptions cgopts;
+        clang::HeaderSearchOptions hs;
+        clang::TargetOptions topts;
+        llvm::LLVMContext ctx;
+        llvm::Module m("foo", ctx);
+        auto os = std::make_unique<llvm::raw_null_ostream>();
+        clang::EmitBackendOutput(m_ast->getASTContext().getDiagnostics(), hs, cgopts,
+                                 topts, *m_ast->GetLangOpts(),
+                                 m_ast->getASTContext().getTargetInfo().getDataLayout(),
+                                 &m, Backend_EmitNothing, std::move(os));
+    });
+  }
+  Pool.wait();
+}
Index: llvm/lib/Support/CommandLine.cpp
===================================================================
--- llvm/lib/Support/CommandLine.cpp
+++ llvm/lib/Support/CommandLine.cpp
@@ -44,6 +44,7 @@
 #include <cstdlib>
 #include <map>
 #include <string>
+#include <unistd.h>
 using namespace llvm;
 using namespace cl;
 
@@ -207,12 +208,16 @@
   void addOption(Option *O, SubCommand *SC) {
     bool HadErrors = false;
     if (O->hasArgStr()) {
+      if (O->ArgStr == "h")
+        llvm::errs() << (void*)SC << "\n";
       // If it's a DefaultOption, check to make sure it isn't already there.
       if (O->isDefaultOption() &&
           SC->OptionsMap.find(O->ArgStr) != SC->OptionsMap.end())
         return;
+      usleep(rand() % 20);
 
       // Add argument to the argument map!
+      llvm::errs() << "Inserting " << O->ArgStr << "\n";
       if (!SC->OptionsMap.insert(std::make_pair(O->ArgStr, O)).second) {
         errs() << ProgramName << ": CommandLine Error: Option '" << O->ArgStr
                << "' registered more than once!\n";
@@ -237,8 +242,10 @@
     // indicate serious issues such as conflicting option names or an
     // incorrectly
     // linked LLVM distribution.
-    if (HadErrors)
+    if (HadErrors) {
+      abort();
       report_fatal_error("inconsistency in registered CommandLine options");
+    }
 
     // If we're adding this to all sub-commands, add it to the ones that have
     // already been registered.
Index: llvm/utils/unittest/UnitTestMain/TestMain.cpp
===================================================================
--- llvm/utils/unittest/UnitTestMain/TestMain.cpp
+++ llvm/utils/unittest/UnitTestMain/TestMain.cpp
@@ -27,7 +27,7 @@
   // Initialize both gmock and gtest.
   testing::InitGoogleMock(&argc, argv);
 
-  llvm::cl::ParseCommandLineOptions(argc, argv);
+  //llvm::cl::ParseCommandLineOptions(argc, argv);
 
   // Make it easy for a test to re-execute itself by saving argv[0].
   TestMainArgv0 = argv[0];