[SYCL] Align behavior of empty command groups with SYCL2020 (#3822)

Signed-off-by: mdimakov <[email protected]>

Author: maximdimakov

sycl/source/handler.cpp

@@ -203,9 +203,13 @@ event handler::finalize() {
         std::move(MRequirements), std::move(MEvents), MCGType, MCodeLoc));
     break;
   case detail::CG::NONE:
-    throw runtime_error("Command group submitted without a kernel or a "
-                        "explicit memory operation.",
-                        PI_INVALID_OPERATION);
+    if (detail::pi::trace(detail::pi::TraceLevel::PI_TRACE_ALL)) {
+      std::cout << "WARNING: An empty command group is submitted." << std::endl;
+    }
+    detail::EventImplPtr Event =
+        std::make_shared<cl::sycl::detail::event_impl>();
+    MLastEvent = detail::createSyclObjFromImpl<event>(Event);
+    return MLastEvent;
   }
 
   if (!CommandGroup)

sycl/test/basic_tests/event_async_exception.cpp

@@ -28,12 +28,13 @@ int main() {
   queue q(asyncHandler);
 
   try {
-    // Submit a CG with no kernel or memory operation to trigger an async error
+    // Check that submitting a CG with no kernel or memory operation doesn't produce
+    // an async exception
     event e = q.submit([&](handler &cgh) {});
 
     e.wait_and_throw();
-    return 1;
-  } catch (runtime_error e) {
     return 0;
+  } catch (runtime_error e) {
+    return 1;
   }
 }