[MLIR] Fix redundant MLIR initialization.

MLIR is now initialize once once in CPU backend.

CMakeLists.txt

@@ -383,6 +383,7 @@ if (NGRAPH_CPU_ENABLE)
 endif()
 
 if (NGRAPH_MLIR_ENABLE)
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DNGRAPH_MLIR_ENABLE")
     set(NGRAPH_MLIR_SOURCE_DIR ${CMAKE_SOURCE_DIR}/src/contrib/mlir)
 endif()
 

src/contrib/mlir/compiler.cpp

@@ -32,6 +32,7 @@
 #include <mlir/Target/LLVMIR.h>
 #include <mlir/Transforms/DialectConversion.h>
 #include <mlir/Transforms/Passes.h>
+#include <mutex>
 #include "dialect/dialect.hpp"
 #include "dialect/type.hpp"
 #include "lowerer.hpp"
@@ -63,9 +64,19 @@ MLIRCompiler::MLIRCompiler(const ngraph::op::CompiledKernel* compiled_kernel,
 
 void MLIRCompiler::init_mlir()
 {
-    mlir::registerDialect<mlir::NGDialect>();
-    // Register any LLVM command line options
-    llvm::cl::ParseEnvironmentOptions("ngraph", "MLIR_LLVM_OPTIONS", "");
+    // Mutex to safely initialize MLIR.
+    static std::mutex mlir_init_mutex;
+    static bool initialized = false;
+
+    std::unique_lock<std::mutex> lock(mlir_init_mutex);
+
+    if (!initialized)
+    {
+        mlir::registerDialect<mlir::NGDialect>();
+        // Register any LLVM command line options
+        llvm::cl::ParseEnvironmentOptions("ngraph", "MLIR_LLVM_OPTIONS", "");
+        initialized = true;
+    }
 }
 
 void MLIRCompiler::compile_and_run()

src/ngraph/runtime/cpu/cpu_backend.cpp

@@ -25,6 +25,11 @@
 #include "ngraph/runtime/cpu/cpu_tensor_view.hpp"
 #include "ngraph/util.hpp"
 
+#ifdef NGRAPH_MLIR_ENABLE
+#include "contrib/mlir/compiler.hpp"
+#endif
+
+
 using namespace ngraph;
 using namespace std;
 
@@ -90,6 +95,14 @@ shared_ptr<runtime::Executable>
                                        ngraph::pass::PassConfig& pass_config,
                                        bool performance_counters_enabled)
 {
+#ifdef NGRAPH_MLIR_ENABLE
+    if (std::getenv("NGRAPH_MLIR") != nullptr)
+    {
+        // Initialize MLIR compiler
+        ngmlir::MLIRCompiler::init_mlir();
+    }
+#endif
+
     shared_ptr<runtime::Executable> rc;
     auto it = m_exec_map.find(func);
     if (it != m_exec_map.end())

src/ngraph/runtime/cpu/cpu_external_function.cpp

@@ -193,9 +193,6 @@
 #include "ngraph/runtime/cpu/pass/cpu_workspace_insertion.hpp"
 #include "ngraph/runtime/cpu/pass/halide_subgraph_extraction.hpp"
 
-#ifdef NGRAPH_MLIR_ENABLE
-#include "contrib/mlir/compiler.hpp"
-#endif
 
 using namespace std;
 using namespace ngraph;
@@ -1400,14 +1397,6 @@ void runtime::cpu::CPU_ExternalFunction::build(ngraph::pass::PassConfig& pass_co
     // After processing inputs, outputs, constants, and intermediates, set the buffer size.
     m_buffer_size = buffer_index;
 
-#ifdef NGRAPH_MLIR_ENABLE
-    if (std::getenv("NGRAPH_MLIR") != nullptr)
-    {
-        // Initialize MLIR compiler
-        ngmlir::MLIRCompiler::init_mlir();
-    }
-#endif
-
     for (shared_ptr<Node> node : m_function->get_ordered_ops())
     {
         if (node->is_parameter() || node->is_constant())