[MLIR][ExecutionEngine] Enable PIC option (#170995)

This PR enables the MLIR execution engine to dump object file as PIC
code, which is needed when the object file is later bundled into a dynamic
shared library.

---------

Co-authored-by: Mehdi Amini <joker.eph@gmail.com>

mlir/include/mlir-c/ExecutionEngine.h

@@ -41,10 +41,13 @@ DEFINE_C_API_STRUCT(MlirExecutionEngine, void);
 /// generation. The number and array of paths corresponding to shared libraries
 /// that will be loaded are specified via `numPaths` and `sharedLibPaths`
 /// respectively.
+/// The `enablePIC` arguments controls the relocation model, when true the
+/// generated code is emitted as "position independent", making it possible to
+/// save it and reload it as a shared object in another process.
 /// TODO: figure out other options.
 MLIR_CAPI_EXPORTED MlirExecutionEngine mlirExecutionEngineCreate(
     MlirModule op, int optLevel, int numPaths,
-    const MlirStringRef *sharedLibPaths, bool enableObjectDump);
+    const MlirStringRef *sharedLibPaths, bool enableObjectDump, bool enablePIC);
 
 /// Initialize the ExecutionEngine. Global constructors specified by
 /// `llvm.mlir.global_ctors` will be run. One common scenario is that kernel

mlir/lib/Bindings/Python/ExecutionEngineModule.cpp

@@ -75,13 +75,13 @@ NB_MODULE(_mlirExecutionEngine, m) {
           "__init__",
           [](PyExecutionEngine &self, MlirModule module, int optLevel,
              const std::vector<std::string> &sharedLibPaths,
-             bool enableObjectDump) {
+             bool enableObjectDump, bool enablePIC) {
             llvm::SmallVector<MlirStringRef, 4> libPaths;
             for (const std::string &path : sharedLibPaths)
               libPaths.push_back({path.c_str(), path.length()});
-            MlirExecutionEngine executionEngine =
-                mlirExecutionEngineCreate(module, optLevel, libPaths.size(),
-                                          libPaths.data(), enableObjectDump);
+            MlirExecutionEngine executionEngine = mlirExecutionEngineCreate(
+                module, optLevel, libPaths.size(), libPaths.data(),
+                enableObjectDump, enablePIC);
             if (mlirExecutionEngineIsNull(executionEngine))
               throw std::runtime_error(
                   "Failure while creating the ExecutionEngine.");
@@ -89,7 +89,7 @@ NB_MODULE(_mlirExecutionEngine, m) {
           },
           nb::arg("module"), nb::arg("opt_level") = 2,
           nb::arg("shared_libs") = nb::list(),
-          nb::arg("enable_object_dump") = true,
+          nb::arg("enable_object_dump") = true, nb::arg("enable_pic") = false,
           "Create a new ExecutionEngine instance for the given Module. The "
           "module must contain only dialects that can be translated to LLVM. "
           "Perform transformations and code generation at the optimization "

mlir/lib/CAPI/ExecutionEngine/ExecutionEngine.cpp

@@ -22,7 +22,7 @@ using namespace mlir;
 extern "C" MlirExecutionEngine
 mlirExecutionEngineCreate(MlirModule op, int optLevel, int numPaths,
                           const MlirStringRef *sharedLibPaths,
-                          bool enableObjectDump) {
+                          bool enableObjectDump, bool enablePIC) {
   static bool initOnce = [] {
     llvm::InitializeNativeTarget();
     llvm::InitializeNativeTargetAsmParser(); // needed for inline_asm
@@ -43,6 +43,8 @@ mlirExecutionEngineCreate(MlirModule op, int optLevel, int numPaths,
     consumeError(tmBuilderOrError.takeError());
     return MlirExecutionEngine{nullptr};
   }
+  if (enablePIC)
+    tmBuilderOrError->setRelocationModel(llvm::Reloc::PIC_);
   auto tmOrError = tmBuilderOrError->createTargetMachine();
   if (!tmOrError) {
     llvm::errs() << "Failed to create a TargetMachine for the host because: \n";
@@ -63,7 +65,8 @@ mlirExecutionEngineCreate(MlirModule op, int optLevel, int numPaths,
   jitOptions.jitCodeGenOptLevel = static_cast<llvm::CodeGenOptLevel>(optLevel);
   jitOptions.sharedLibPaths = libPaths;
   jitOptions.enableObjectDump = enableObjectDump;
-  auto jitOrError = ExecutionEngine::create(unwrap(op), jitOptions);
+  auto jitOrError = ExecutionEngine::create(unwrap(op), jitOptions,
+                                            std::move(tmOrError.get()));
   if (!jitOrError) {
     llvm::errs() << "Failed to create an ExecutionEngine because: \n";
     consumeError(jitOrError.takeError());

mlir/test/CAPI/execution_engine.c

@@ -69,7 +69,7 @@ void testSimpleExecution(void) {
   mlirRegisterAllLLVMTranslations(ctx);
   MlirExecutionEngine jit = mlirExecutionEngineCreate(
       module, /*optLevel=*/2, /*numPaths=*/0, /*sharedLibPaths=*/NULL,
-      /*enableObjectDump=*/false);
+      /*enableObjectDump=*/false, /*enablePIC=*/false);
   if (mlirExecutionEngineIsNull(jit)) {
     fprintf(stderr, "Execution engine creation failed");
     exit(2);
@@ -125,7 +125,7 @@ void testOmpCreation(void) {
   // against the OpenMP library.
   MlirExecutionEngine jit = mlirExecutionEngineCreate(
       module, /*optLevel=*/2, /*numPaths=*/0, /*sharedLibPaths=*/NULL,
-      /*enableObjectDump=*/false);
+      /*enableObjectDump=*/false, /*enablePIC=*/false);
   if (mlirExecutionEngineIsNull(jit)) {
     fprintf(stderr, "Engine creation failed with OpenMP");
     exit(2);

mlir/test/CAPI/global_constructors.c

@@ -79,7 +79,7 @@ void testGlobalCtorJitCallback(void) {
   // Create execution engine with initialization disabled
   MlirExecutionEngine jit = mlirExecutionEngineCreate(
       module, /*optLevel=*/2, /*numPaths=*/0, /*sharedLibPaths=*/NULL,
-      /*enableObjectDump=*/false);
+      /*enableObjectDump=*/false, /*enablePIC=*/false);
 
   if (mlirExecutionEngineIsNull(jit)) {
     fprintf(stderr, "Execution engine creation failed");

mlir/test/python/execution_engine.py

@@ -807,6 +807,7 @@ def testDumpToObjectFile():
                 # because RTDyldObjectLinkingLayer::emit will try to resolve symbols before dumping
                 # (see the jitLinkForORC call at the bottom there).
                 shared_libs=[MLIR_C_RUNNER_UTILS],
+                enable_pic=True,
             )
 
             # CHECK: Object file exists: True