[SYCL] Exception was removed from empty cg

sycl/source/handler.cpp

@@ -202,18 +202,26 @@ 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 << "The empty command group is supported by sycl2020"
+                << std::endl;
+    }
+    break;
   }
 
-  if (!CommandGroup)
-    throw sycl::runtime_error(
-        "Internal Error. Command group cannot be constructed.",
-        PI_INVALID_OPERATION);
-
-  detail::EventImplPtr Event = detail::Scheduler::getInstance().addCG(
-      std::move(CommandGroup), std::move(MQueue));
+  detail::EventImplPtr Event;
+
+  if (!CommandGroup) {
+    if (getType() != detail::CG::NONE)
+      throw sycl::runtime_error(
+          "Internal Error. Command group cannot be constructed.",
+          PI_INVALID_OPERATION);
+    else
+      // empty cg is supported by sycl2020
+      Event = std::make_shared<cl::sycl::detail::event_impl>();
+  } else
+    Event = detail::Scheduler::getInstance().addCG(std::move(CommandGroup),
+                                                   std::move(MQueue));
 
   MLastEvent = detail::createSyclObjFromImpl<event>(Event);
   return MLastEvent;

sycl/test/basic_tests/event_async_exception.cpp

@@ -28,12 +28,12 @@ int main() {
   queue q(asyncHandler);
 
   try {
-    // Submit a CG with no kernel or memory operation to trigger an async error
+    // Submit a CG with no kernel or memory operation no trigger an async error
     event e = q.submit([&](handler &cgh) {});
 
     e.wait_and_throw();
-    return 1;
-  } catch (runtime_error e) {
     return 0;
+  } catch (runtime_error e) {
+    return 1;
   }
 }