CPU: Allow the use of precompiled headers when compiling generated code

This reduces compilation time by ~10x

src/ngraph/codegen/compiler.cpp

@@ -67,6 +67,7 @@ static std::string GetExecutablePath(const char* Argv0)
 
 execution_state::execution_state()
     : m_execution_engine{nullptr}
+    , pch_enabled(false)
 {
 }
 
@@ -151,8 +152,17 @@ std::unique_ptr<llvm::Module> execution_state::compile(const string& source, con
 
     // CodeGen options
     auto& CGO = Clang->getInvocation().getCodeGenOpts();
+    // TODO: Debuginfo inclusion should be predicated
     CGO.setDebugInfo(codegenoptions::FullDebugInfo);
 
+    if (pch_enabled)
+    {
+        // Preprocessor options
+        auto& PPO = Clang->getInvocation().getPreprocessorOpts();
+        PPO.ImplicitPCHInclude = "ngcpu.pch";
+        PPO.DisablePCHValidation = 1;
+    }
+
     // Map code filename to a memoryBuffer
     StringRef source_ref(source);
     unique_ptr<MemoryBuffer> buffer = MemoryBuffer::getMemBufferCopy(source_ref);

src/ngraph/codegen/compiler.hpp

@@ -44,6 +44,9 @@ public:
     execution_state();
     ~execution_state();
 
+    void enable_pch() { pch_enabled = true; }
+    void disable_pch() { pch_enabled = false; }
+
     std::unique_ptr<llvm::Module> compile(const std::string& source, const std::string& name = "");
 
     bool add_module(std::unique_ptr<llvm::Module>&);
@@ -61,6 +64,7 @@ public:
 private:
     llvm::ExecutionEngine* m_execution_engine;
     std::string jit_error;
+    bool pch_enabled;
 
     template <typename signature>
     std::function<signature> f_cast(void* f)

src/ngraph/runtime/cpu/external_function.cpp

@@ -59,6 +59,10 @@
 #include "ngraph/runtime/cpu/external_function.hpp"
 #include "ngraph/runtime/utils.hpp"
 
+// TODO: Decide if we want to ship this or
+// just enable it for developer build-test cycles
+#define NGCPU_PCH
+
 using namespace std;
 using namespace ngraph::runtime::cpu;
 
@@ -176,7 +180,7 @@ using namespace ngraph::element;
 using namespace ngraph::runtime;
 using namespace ngraph::runtime::cpu::eigen;
 
-extern "C" void __entrypoint(ngraph::runtime::cpu::CallFrame* call_frame, 
+extern "C" void __entrypoint(ngraph::runtime::cpu::CallFrame* call_frame,
                              ngraph::runtime::TensorViewPtrs& tensor_views)
 {
 )";
@@ -215,6 +219,11 @@ extern "C" void __entrypoint(ngraph::runtime::cpu::CallFrame* call_frame,
     out.close();
 
     ngraph::codegen::execution_state estate;
+
+#if defined(NGCPU_PCH)
+    estate.enable_pch();
+#endif
+
     auto llvm_module = estate.compile(TU, "__ngcpu_codegen.cpp");
     assert(llvm_module);
     estate.add_module(llvm_module);