[Beignet] [PATCH v2] improve multithread calling of llvm

[Homer Hsing]

call llvm multithread function instead of using a semaphore.
also exit llvm multithread mode at the end of life.

v2: not call llvm::shutdown() if llvm is older than 3.4
Signed-off-by: Homer Hsing <homer.xing at intel.com>
---
 backend/src/backend/gen_program.cpp |  7 -------
 backend/src/backend/gen_program.h   |  2 --
 backend/src/backend/program.cpp     | 13 ++++++++++---
 3 files changed, 10 insertions(+), 12 deletions(-)

diff --git a/backend/src/backend/gen_program.cpp b/backend/src/backend/gen_program.cpp
index 781152d..40ab176 100644
--- a/backend/src/backend/gen_program.cpp
+++ b/backend/src/backend/gen_program.cpp
@@ -159,10 +159,3 @@ void genSetupCallBacks(void)
   gbe_program_new_from_binary = gbe::genProgramNewFromBinary;
   gbe_program_new_from_llvm = gbe::genProgramNewFromLLVM;
 }
-
-sem_t llvm_semaphore;
-
-void genSetupLLVMSemaphore(void)
-{
-  sem_init(&llvm_semaphore, 0, 1);
-}
diff --git a/backend/src/backend/gen_program.h b/backend/src/backend/gen_program.h
index a498a5d..8d37a70 100644
--- a/backend/src/backend/gen_program.h
+++ b/backend/src/backend/gen_program.h
@@ -33,8 +33,6 @@
 
 /*! This will make the compiler output Gen ISA code */
 extern void genSetupCallBacks(void);
-extern sem_t llvm_semaphore;
-extern void genSetupLLVMSemaphore(void);
 
 #endif /* __GBE_GEN_PROGRAM_H__ */
 
diff --git a/backend/src/backend/program.cpp b/backend/src/backend/program.cpp
index 937f95b..25be484 100644
--- a/backend/src/backend/program.cpp
+++ b/backend/src/backend/program.cpp
@@ -32,6 +32,8 @@
 #include "ir/unit.hpp"
 #include "llvm/llvm_to_gen.hpp"
 #include "llvm/Config/config.h"
+#include "llvm/Support/Threading.h"
+#include "llvm/Support/ManagedStatic.h"
 #include <cstring>
 #include <algorithm>
 #include <fstream>
@@ -557,9 +559,7 @@ namespace gbe {
 
     // Create an action and make the compiler instance carry it out
     llvm::OwningPtr<clang::CodeGenAction> Act(new clang::EmitLLVMOnlyAction());
-    sem_wait(&llvm_semaphore);
     auto retVal = Clang.ExecuteAction(*Act);
-    sem_post(&llvm_semaphore);
     if (!retVal)
       return;
 
@@ -854,7 +854,14 @@ namespace gbe
       gbe_get_image_base_index = gbe::getImageBaseIndex;
       gbe_set_image_base_index = gbe::setImageBaseIndex;
       genSetupCallBacks();
-      genSetupLLVMSemaphore();
+      llvm::llvm_start_multithreaded();
+    }
+
+    ~CallBackInitializer() {
+      llvm::llvm_stop_multithreaded();
+#if (LLVM_VERSION_MAJOR == 3) && (LLVM_VERSION_MINOR > 3)
+      llvm::llvm_shutdown();
+#endif
     }
   };
 
-- 
1.8.3.2