[NFC][msan] Split ThreadStart and Init

Author: vitalybuka

compiler-rt/lib/msan/msan.cpp

@@ -470,7 +470,7 @@ void __msan_init() {
 
   MsanThread *main_thread = MsanThread::Create(nullptr, nullptr);
   SetCurrentThread(main_thread);
-  main_thread->ThreadStart();
+  main_thread->Init();
 
 #if MSAN_CONTAINS_UBSAN
   __ubsan::InitAsPlugin();

compiler-rt/lib/msan/msan_interceptors.cpp

@@ -1033,6 +1033,7 @@ extern "C" int pthread_attr_destroy(void *attr);
 static void *MsanThreadStartFunc(void *arg) {
   MsanThread *t = (MsanThread *)arg;
   SetCurrentThread(t);
+  t->Init();
   return t->ThreadStart();
 }
 

compiler-rt/lib/msan/msan_thread.cpp

@@ -65,20 +65,7 @@ void MsanThread::Destroy() {
   DTLS_Destroy();
 }
 
-thread_return_t MsanThread::ThreadStart() {
-  Init();
-
-  if (!start_routine_) {
-    // start_routine_ == 0 if we're on the main thread or on one of the
-    // OS X libdispatch worker threads. But nobody is supposed to call
-    // ThreadStart() for the worker threads.
-    return 0;
-  }
-
-  thread_return_t res = start_routine_(arg_);
-
-  return res;
-}
+thread_return_t MsanThread::ThreadStart() { return start_routine_(arg_); }
 
 MsanThread::StackBounds MsanThread::GetStackBounds() const {
   if (!stack_switching_)