Revert recent LLVM threading changes that break the mingw build

docs/ProgrammersManual.rst

@@ -2170,25 +2170,67 @@ compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and
 using the resultant compiler to build a copy of LLVM with multithreading
 support.
 
+.. _startmultithreaded:
+
+Entering and Exiting Multithreaded Mode
+---------------------------------------
+
+In order to properly protect its internal data structures while avoiding
+excessive locking overhead in the single-threaded case, the LLVM must intialize
+certain data structures necessary to provide guards around its internals.  To do
+so, the client program must invoke ``llvm_start_multithreaded()`` before making
+any concurrent LLVM API calls.  To subsequently tear down these structures, use
+the ``llvm_stop_multithreaded()`` call.  You can also use the
+``llvm_is_multithreaded()`` call to check the status of multithreaded mode.
+
+Note that both of these calls must be made *in isolation*.  That is to say that
+no other LLVM API calls may be executing at any time during the execution of
+``llvm_start_multithreaded()`` or ``llvm_stop_multithreaded``.  It is the
+client's responsibility to enforce this isolation.
+
+The return value of ``llvm_start_multithreaded()`` indicates the success or
+failure of the initialization.  Failure typically indicates that your copy of
+LLVM was built without multithreading support, typically because GCC atomic
+intrinsics were not found in your system compiler.  In this case, the LLVM API
+will not be safe for concurrent calls.  However, it *will* be safe for hosting
+threaded applications in the JIT, though :ref:`care must be taken
+<jitthreading>` to ensure that side exits and the like do not accidentally
+result in concurrent LLVM API calls.
+
 .. _shutdown:
 
 Ending Execution with ``llvm_shutdown()``
 -----------------------------------------
 
 When you are done using the LLVM APIs, you should call ``llvm_shutdown()`` to
-deallocate memory used for internal structures.
+deallocate memory used for internal structures.  This will also invoke
+``llvm_stop_multithreaded()`` if LLVM is operating in multithreaded mode.  As
+such, ``llvm_shutdown()`` requires the same isolation guarantees as
+``llvm_stop_multithreaded()``.
+
+Note that, if you use scope-based shutdown, you can use the
+``llvm_shutdown_obj`` class, which calls ``llvm_shutdown()`` in its destructor.
 
 .. _managedstatic:
 
 Lazy Initialization with ``ManagedStatic``
 ------------------------------------------
 
 ``ManagedStatic`` is a utility class in LLVM used to implement static
-initialization of static resources, such as the global type tables.  In a
-single-threaded environment, it implements a simple lazy initialization scheme.
-When LLVM is compiled with support for multi-threading, however, it uses
+initialization of static resources, such as the global type tables.  Before the
+invocation of ``llvm_shutdown()``, it implements a simple lazy initialization
+scheme.  Once ``llvm_start_multithreaded()`` returns, however, it uses
 double-checked locking to implement thread-safe lazy initialization.
 
+Note that, because no other threads are allowed to issue LLVM API calls before
+``llvm_start_multithreaded()`` returns, it is possible to have
+``ManagedStatic``\ s of ``llvm::sys::Mutex``\ s.
+
+The ``llvm_acquire_global_lock()`` and ``llvm_release_global_lock`` APIs provide
+access to the global lock used to implement the double-checked locking for lazy
+initialization.  These should only be used internally to LLVM, and only if you
+know what you're doing!
+
 .. _llvmcontext:
 
 Achieving Isolation with ``LLVMContext``

include/llvm-c/Core.h

@@ -2848,13 +2848,16 @@ void LLVMDisposePassManager(LLVMPassManagerRef PM);
  * @{
  */
 
-/** Deprecated: Multi-threading can only be enabled/disabled with the compile
-    time define LLVM_ENABLE_THREADS.  This function always returns
-    LLVMIsMultithreaded(). */
+/** Allocate and initialize structures needed to make LLVM safe for
+    multithreading. The return value indicates whether multithreaded
+    initialization succeeded. Must be executed in isolation from all
+    other LLVM api calls.
+    @see llvm::llvm_start_multithreaded */
 LLVMBool LLVMStartMultithreaded(void);
 
-/** Deprecated: Multi-threading can only be enabled/disabled with the compile
-    time define LLVM_ENABLE_THREADS. */
+/** Deallocate structures necessary to make LLVM safe for multithreading.
+    Must be executed in isolation from all other LLVM api calls.
+    @see llvm::llvm_stop_multithreaded */
 void LLVMStopMultithreaded(void);
 
 /** Check whether LLVM is executing in thread-safe mode or not.

include/llvm/ExecutionEngine/ExecutionEngine.h

@@ -22,10 +22,10 @@
 #include "llvm/IR/ValueMap.h"
 #include "llvm/MC/MCCodeGenInfo.h"
 #include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/Mutex.h"
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Target/TargetOptions.h"
 #include <map>
-#include <mutex>
 #include <string>
 #include <vector>
 
@@ -42,6 +42,7 @@ class JITEventListener;
 class JITMemoryManager;
 class MachineCodeInfo;
 class Module;
+class MutexGuard;
 class ObjectCache;
 class RTDyldMemoryManager;
 class Triple;
@@ -58,7 +59,7 @@ class ExecutionEngineState {
 public:
   struct AddressMapConfig : public ValueMapConfig<const GlobalValue*> {
     typedef ExecutionEngineState *ExtraData;
-    static std::recursive_mutex *getMutex(ExecutionEngineState *EES);
+    static sys::Mutex *getMutex(ExecutionEngineState *EES);
     static void onDelete(ExecutionEngineState *EES, const GlobalValue *Old);
     static void onRAUW(ExecutionEngineState *, const GlobalValue *,
                        const GlobalValue *);
@@ -163,7 +164,7 @@ class ExecutionEngine {
   /// lock - This lock protects the ExecutionEngine, MCJIT, JIT, JITResolver and
   /// JITEmitter classes.  It must be held while changing the internal state of
   /// any of those classes.
-  std::recursive_mutex lock;
+  sys::Mutex lock;
 
   //===--------------------------------------------------------------------===//
   //  ExecutionEngine Startup

include/llvm/IR/ValueMap.h

@@ -28,9 +28,9 @@
 
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/IR/ValueHandle.h"
+#include "llvm/Support/Mutex.h"
 #include "llvm/Support/type_traits.h"
 #include <iterator>
-#include <mutex>
 
 namespace llvm {
 
@@ -45,7 +45,7 @@ class ValueMapConstIterator;
 /// This class defines the default behavior for configurable aspects of
 /// ValueMap<>.  User Configs should inherit from this class to be as compatible
 /// as possible with future versions of ValueMap.
-template<typename KeyT, typename MutexT = std::recursive_mutex>
+template<typename KeyT, typename MutexT = sys::Mutex>
 struct ValueMapConfig {
   typedef MutexT mutex_type;
 
@@ -216,11 +216,11 @@ class ValueMapCallbackVH : public CallbackVH {
     ValueMapCallbackVH Copy(*this);
     typename Config::mutex_type *M = Config::getMutex(Copy.Map->Data);
     if (M)
-      M->lock();
+      M->acquire();
     Config::onDelete(Copy.Map->Data, Copy.Unwrap());  // May destroy *this.
     Copy.Map->Map.erase(Copy);  // Definitely destroys *this.
     if (M)
-      M->unlock();
+      M->release();
   }
   void allUsesReplacedWith(Value *new_key) override {
     assert(isa<KeySansPointerT>(new_key) &&
@@ -229,7 +229,7 @@ class ValueMapCallbackVH : public CallbackVH {
     ValueMapCallbackVH Copy(*this);
     typename Config::mutex_type *M = Config::getMutex(Copy.Map->Data);
     if (M)
-      M->lock();
+      M->acquire();
 
     KeyT typed_new_key = cast<KeySansPointerT>(new_key);
     // Can destroy *this:
@@ -245,7 +245,7 @@ class ValueMapCallbackVH : public CallbackVH {
       }
     }
     if (M)
-      M->unlock();
+      M->release();
   }
 };
 

include/llvm/Support/ManagedStatic.h

@@ -103,6 +103,9 @@ void llvm_shutdown();
 /// llvm_shutdown() when it is destroyed.
 struct llvm_shutdown_obj {
   llvm_shutdown_obj() { }
+  explicit llvm_shutdown_obj(bool multithreaded) {
+    if (multithreaded) llvm_start_multithreaded();
+  }
   ~llvm_shutdown_obj() { llvm_shutdown(); }
 };
 

include/llvm/Support/Threading.h

@@ -7,19 +7,40 @@
 //
 //===----------------------------------------------------------------------===//
 //
-// This file declares helper functions for running LLVM in a multi-threaded
-// environment.
+// TThis file defines llvm_start_multithreaded() and friends.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_SUPPORT_THREADING_H
 #define LLVM_SUPPORT_THREADING_H
 
 namespace llvm {
-  /// Returns true if LLVM is compiled with support for multi-threading, and
-  /// false otherwise.
+  /// llvm_start_multithreaded - Allocate and initialize structures needed to
+  /// make LLVM safe for multithreading.  The return value indicates whether
+  /// multithreaded initialization succeeded.  LLVM will still be operational
+  /// on "failed" return, and will still be safe for hosting threading
+  /// applications in the JIT, but will not be safe for concurrent calls to the
+  /// LLVM APIs.
+  /// THIS MUST EXECUTE IN ISOLATION FROM ALL OTHER LLVM API CALLS.
+  bool llvm_start_multithreaded();
+
+  /// llvm_stop_multithreaded - Deallocate structures necessary to make LLVM
+  /// safe for multithreading.
+  /// THIS MUST EXECUTE IN ISOLATION FROM ALL OTHER LLVM API CALLS.
+  void llvm_stop_multithreaded();
+
+  /// llvm_is_multithreaded - Check whether LLVM is executing in thread-safe
+  /// mode or not.
   bool llvm_is_multithreaded();
 
+  /// acquire_global_lock - Acquire the global lock.  This is a no-op if called
+  /// before llvm_start_multithreaded().
+  void llvm_acquire_global_lock();
+
+  /// release_global_lock - Release the global lock.  This is a no-op if called
+  /// before llvm_start_multithreaded().
+  void llvm_release_global_lock();
+
   /// llvm_execute_on_thread - Execute the given \p UserFn on a separate
   /// thread, passing it the provided \p UserData.
   ///

lib/ExecutionEngine/ExecutionEngine.cpp

@@ -166,7 +166,7 @@ void *ExecutionEngineState::RemoveMapping(const GlobalValue *ToUnmap) {
 }
 
 void ExecutionEngine::addGlobalMapping(const GlobalValue *GV, void *Addr) {
-  std::lock_guard<std::recursive_mutex> locked(lock);
+  MutexGuard locked(lock);
 
   DEBUG(dbgs() << "JIT: Map \'" << GV->getName()
         << "\' to [" << Addr << "]\n";);
@@ -184,14 +184,14 @@ void ExecutionEngine::addGlobalMapping(const GlobalValue *GV, void *Addr) {
 }
 
 void ExecutionEngine::clearAllGlobalMappings() {
-  std::lock_guard<std::recursive_mutex> locked(lock);
+  MutexGuard locked(lock);
 
   EEState.getGlobalAddressMap().clear();
   EEState.getGlobalAddressReverseMap().clear();
 }
 
 void ExecutionEngine::clearGlobalMappingsFromModule(Module *M) {
-  std::lock_guard<std::recursive_mutex> locked(lock);
+  MutexGuard locked(lock);
 
   for (Module::iterator FI = M->begin(), FE = M->end(); FI != FE; ++FI)
     EEState.RemoveMapping(FI);
@@ -201,7 +201,7 @@ void ExecutionEngine::clearGlobalMappingsFromModule(Module *M) {
 }
 
 void *ExecutionEngine::updateGlobalMapping(const GlobalValue *GV, void *Addr) {
-  std::lock_guard<std::recursive_mutex> locked(lock);
+  MutexGuard locked(lock);
 
   ExecutionEngineState::GlobalAddressMapTy &Map =
     EEState.getGlobalAddressMap();
@@ -228,15 +228,15 @@ void *ExecutionEngine::updateGlobalMapping(const GlobalValue *GV, void *Addr) {
 }
 
 void *ExecutionEngine::getPointerToGlobalIfAvailable(const GlobalValue *GV) {
-  std::lock_guard<std::recursive_mutex> locked(lock);
+  MutexGuard locked(lock);
 
   ExecutionEngineState::GlobalAddressMapTy::iterator I =
     EEState.getGlobalAddressMap().find(GV);
   return I != EEState.getGlobalAddressMap().end() ? I->second : nullptr;
 }
 
 const GlobalValue *ExecutionEngine::getGlobalValueAtAddress(void *Addr) {
-  std::lock_guard<std::recursive_mutex> locked(lock);
+  MutexGuard locked(lock);
 
   // If we haven't computed the reverse mapping yet, do so first.
   if (EEState.getGlobalAddressReverseMap().empty()) {
@@ -555,7 +555,7 @@ void *ExecutionEngine::getPointerToGlobal(const GlobalValue *GV) {
   if (Function *F = const_cast<Function*>(dyn_cast<Function>(GV)))
     return getPointerToFunction(F);
 
-  std::lock_guard<std::recursive_mutex> locked(lock);
+  MutexGuard locked(lock);
   if (void *P = EEState.getGlobalAddressMap()[GV])
     return P;
 
@@ -1346,7 +1346,7 @@ ExecutionEngineState::ExecutionEngineState(ExecutionEngine &EE)
   : EE(EE), GlobalAddressMap(this) {
 }
 
-std::recursive_mutex *
+sys::Mutex *
 ExecutionEngineState::AddressMapConfig::getMutex(ExecutionEngineState *EES) {
   return &EES->EE.lock;
 }