[SYCL] Fast launch of kernels that have no dependencies

sycl/source/detail/scheduler/commands.hpp

@@ -542,6 +542,7 @@ class ExecCGCommand : public Command {
   std::unique_ptr<detail::CG> MCommandGroup;
 
   friend class Command;
+  friend class Scheduler;
 };
 
 class UpdateHostRequirementCommand : public Command {

sycl/source/detail/scheduler/scheduler.cpp

@@ -86,6 +86,59 @@ EventImplPtr Scheduler::addCG(std::unique_ptr<detail::CG> CommandGroup,
         initStream(Stream, Queue);
       }
     }
+
+    if (CommandGroup->MRequirements.size() + CommandGroup->MEvents.size() ==
+        0) {
+      ExecCGCommand *NewCmd(
+          new ExecCGCommand(std::move(CommandGroup), std::move(Queue)));
+      if (!NewCmd)
+        throw runtime_error("Out of host memory", PI_OUT_OF_HOST_MEMORY);
+      NewEvent = NewCmd->getEvent();
+
+      auto CleanUp = [&]() {
+        NewEvent->setCommand(nullptr);
+        delete NewCmd;
+      };
+
+      if (MGraphBuilder
+              .MPrintOptionsArray[GraphBuilder::PrintOptions::BeforeAddCG])
+        MGraphBuilder.printGraphAsDot("before_addCG");
+      if (MGraphBuilder
+              .MPrintOptionsArray[GraphBuilder::PrintOptions::AfterAddCG])
+        MGraphBuilder.printGraphAsDot("after_addCG");
+
+      try {
+#ifdef XPTI_ENABLE_INSTRUMENTATION
+        NewCmd->emitInstrumentation(xpti::trace_task_begin, nullptr);
+#endif
+
+        cl_int Res = NewCmd->enqueueImp();
+
+        // Emit this correlation signal before the task end
+        NewCmd->emitEnqueuedEventSignal(NewEvent->getHandleRef());
+#ifdef XPTI_ENABLE_INSTRUMENTATION
+        NewCmd->emitInstrumentation(xpti::trace_task_end, nullptr);
+#endif
+
+        if (CL_SUCCESS != Res)
+          throw runtime_error("Enqueue process failed.", PI_INVALID_OPERATION);
+        else if (NewEvent->is_host() || NewEvent->getHandleRef() == nullptr)
+          NewEvent->setComplete();
+      } catch (...) {
+        // enqueueImp() func and if statement above may throw an exception,
+        // so destroy required resources to avoid memory leak
+        CleanUp();
+        std::rethrow_exception(std::current_exception());
+      }
+
+      CleanUp();
+
+      for (auto StreamImplPtr : Streams) {
+        StreamImplPtr->flush();
+      }
+
+      return NewEvent;
+    }
   }
 
   {

sycl/source/detail/scheduler/scheduler.hpp

@@ -612,6 +612,7 @@ class Scheduler {
                                         const ContextImplPtr &Context);
 
     friend class Command;
+    friend class Scheduler;
 
   private:
     friend class ::MockScheduler;