Remove support for runtime multi-threading.

This patch removes the functions llvm_start_multithreaded() and
llvm_stop_multithreaded(), and changes llvm_is_multithreaded()
to return a constant value based on the value of the compile-time
definition LLVM_ENABLE_THREADS.

Previously, it was possible to have compile-time support for
threads on, and runtime support for threads off, in which case
certain mutexes were not allocated or ever acquired.  Now, if the
build is created with threads enabled, mutexes are always acquired.

A test before/after patch of compiling a very large TU showed no
noticeable performance impact of this change.

Reviewers: rnk

Differential Revision: http://reviews.llvm.org/D4076

llvm-svn: 210600

1 files changed, 5 insertions, 36 deletions

diff --git a/llvm/lib/Support/Threading.cpp b/llvm/lib/Support/Threading.cpp
index 1acfa79b11d..c9f0f2c2e5a 100644
--- a/llvm/lib/Support/Threading.cpp
+++ b/llvm/lib/Support/Threading.cpp
@@ -19,50 +19,19 @@
 
 using namespace llvm;
 
-static bool multithreaded_mode = false;
-
-static sys::Mutex* global_lock = nullptr;
+llvm::recursive_mutex& llvm::llvm_get_global_lock() {
+  static llvm::recursive_mutex global_lock;
+  return global_lock;
+}
 
-bool llvm::llvm_start_multithreaded() {
+bool llvm::llvm_is_multithreaded() {
 #if LLVM_ENABLE_THREADS != 0
-  assert(!multithreaded_mode && "Already multithreaded!");
-  multithreaded_mode = true;
-  global_lock = new sys::Mutex(true);
-
-  // We fence here to ensure that all initialization is complete BEFORE we
-  // return from llvm_start_multithreaded().
-  sys::MemoryFence();
   return true;
 #else
   return false;
 #endif
 }
 
-void llvm::llvm_stop_multithreaded() {
-#if LLVM_ENABLE_THREADS != 0
-  assert(multithreaded_mode && "Not currently multithreaded!");
-
-  // We fence here to insure that all threaded operations are complete BEFORE we
-  // return from llvm_stop_multithreaded().
-  sys::MemoryFence();
-
-  multithreaded_mode = false;
-  delete global_lock;
-#endif
-}
-
-bool llvm::llvm_is_multithreaded() {
-  return multithreaded_mode;
-}
-
-void llvm::llvm_acquire_global_lock() {
-  if (multithreaded_mode) global_lock->acquire();
-}
-
-void llvm::llvm_release_global_lock() {
-  if (multithreaded_mode) global_lock->release();
-}
-
 #if LLVM_ENABLE_THREADS != 0 && defined(HAVE_PTHREAD_H)
 #include <pthread.h>