[MLIR][ExecutionEngine] don't dump decls (llvm#164478)

Currently ExecutionEngine tries to dump all functions declared in the
module, even those which are "external" (i.e., linked/loaded at
runtime). E.g.

```mlir
func.func private @printF32(f32)
func.func @supported_arg_types(%arg0: i32, %arg1: f32) {
  call @printF32(%arg1) : (f32) -> ()
  return
}
```
fails with
```
Could not compile printF32:
  Symbols not found: [ __mlir_printF32 ]
Program aborted due to an unhandled Error:
Symbols not found: [ __mlir_printF32 ]
```
even though `printF32` can be provided at final build time (i.e., when
the object file is linked to some executable or shlib). E.g, if our own
`libmlir_c_runner_utils` is linked.

So just skip functions which have no bodies during dump (i.e., are decls
without defns).

Author: makslevental

mlir/lib/ExecutionEngine/ExecutionEngine.cpp

@@ -239,6 +239,8 @@ ExecutionEngine::create(Operation *m, const ExecutionEngineOptions &options,
   // Remember all entry-points if object dumping is enabled.
   if (options.enableObjectDump) {
     for (auto funcOp : m->getRegion(0).getOps<LLVM::LLVMFuncOp>()) {
+      if (funcOp.getBlocks().empty())
+        continue;
       StringRef funcName = funcOp.getSymName();
       engine->functionNames.push_back(funcName.str());
     }

mlir/test/python/CMakeLists.txt

@@ -11,7 +11,7 @@ add_public_tablegen_target(MLIRPythonTestIncGen)
 
 add_subdirectory(lib)
 
-set(MLIR_PYTHON_TEST_DEPENDS MLIRPythonModules)
+set(MLIR_PYTHON_TEST_DEPENDS MLIRPythonModules mlir-runner)
 if(NOT MLIR_STANDALONE_BUILD)
   list(APPEND MLIR_PYTHON_TEST_DEPENDS FileCheck count not)
 endif()

mlir/test/python/execution_engine.py

@@ -1,6 +1,7 @@
 # RUN: env MLIR_RUNNER_UTILS=%mlir_runner_utils MLIR_C_RUNNER_UTILS=%mlir_c_runner_utils %PYTHON %s 2>&1 | FileCheck %s
 # REQUIRES: host-supports-jit
 import gc, sys, os, tempfile
+from textwrap import dedent
 from mlir.ir import *
 from mlir.passmanager import *
 from mlir.execution_engine import *
@@ -21,6 +22,7 @@
     "MLIR_C_RUNNER_UTILS", "../../../../lib/libmlir_c_runner_utils.so"
 )
 
+
 # Log everything to stderr and flush so that we have a unified stream to match
 # errors/info emitted by MLIR to stderr.
 def log(*args):
@@ -337,6 +339,7 @@ def callback(a):
             ctypes.pointer(ctypes.pointer(get_ranked_memref_descriptor(inp_arr))),
         )
 
+
 run(testUnrankedMemRefWithOffsetCallback)
 
 
@@ -785,15 +788,25 @@ def testDumpToObjectFile():
     try:
         with Context():
             module = Module.parse(
-                """
-        module {
-        func.func @main() attributes { llvm.emit_c_interface } {
-          return
-        }
-      }"""
+                dedent(
+                    """
+                    func.func private @printF32(f32)
+                    func.func @main(%arg0: f32) attributes { llvm.emit_c_interface } {
+                      call @printF32(%arg0) : (f32) -> ()
+                      return
+                    }
+                    """
+                )
             )
 
-            execution_engine = ExecutionEngine(lowerToLLVM(module), opt_level=3)
+            execution_engine = ExecutionEngine(
+                lowerToLLVM(module),
+                opt_level=3,
+                # Loading MLIR_C_RUNNER_UTILS is necessary even though we don't actually run the code (i.e., call printF32)
+                # because RTDyldObjectLinkingLayer::emit will try to resolve symbols before dumping
+                # (see the jitLinkForORC call at the bottom there).
+                shared_libs=[MLIR_C_RUNNER_UTILS],
+            )
 
             # CHECK: Object file exists: True
             print(f"Object file exists: {os.path.exists(object_path)}")