[mlir-cpu-runner] Check entry function is void

[c-rhodes]

Summary

Currently crashes if function isn't void when specifiying
'-entry-point-result=void'.

mlir/lib/ExecutionEngine/JitRunner.cpp

 
 static Error compileAndExecuteVoidFunction(
     Options &options, Operation *module, StringRef entryPoint,
     CompileAndExecuteConfig config, std::unique_ptr<llvm::TargetMachine> tm) {
   auto mainFunction = dyn_cast_or_null<LLVM::LLVMFuncOp>(
       SymbolTable::lookupSymbolIn(module, entryPoint));
   if (!mainFunction || mainFunction.empty())
     return makeStringError("entry point not found");
+
+  auto resultType = dyn_cast<LLVM::LLVMVoidType>(
+      mainFunction.getFunctionType().getReturnType());
+  if (!resultType)
+    return makeStringError("expected void function");
+
   void *empty = nullptr;
   return compileAndExecute(options, module, entryPoint, std::move(config),
                            &empty, std::move(tm));
 }
 
 template <typename Type>
 Error checkCompatibleReturnType(LLVM::LLVMFuncOp mainFunction);
 template <>

mlir/test/mlir-cpu-runner/verify-entry-point-result.mlir

+// RUN: not mlir-cpu-runner %s -e entry -entry-point-result=void 2>&1 | FileCheck %s
+
+// CHECK: Error: expected void function
+llvm.func @entry() -> (i32) {
+  %0 = llvm.mlir.constant(0 : index) : i32
+  llvm.return %0 : i32
+}