[SYCL] Fix depends_on with default-constructed events

sycl/source/detail/event_impl.hpp

@@ -212,6 +212,15 @@ class event_impl {
   }
   bool needsCleanupAfterWait() { return MNeedsCleanupAfterWait; }
 
+  /// Checks if an event is in a fully intialized state. Default-constructed
+  /// events will return true only after having initialized its native event,
+  /// while other events will assume that they are fully initialized at
+  /// construction, relying on external sources to supply member data.
+  ///
+  /// \return true if the event is considered to be in a fully initialized
+  /// state.
+  bool isInitialized() const noexcept { return MIsInitialized; }
+
 private:
   // When instrumentation is enabled emits trace event for event wait begin and
   // returns the telemetry event generated for the wait

sycl/source/detail/queue_impl.hpp

@@ -530,7 +530,8 @@ class queue_impl {
     // Host and interop tasks, however, are not submitted to low-level runtimes
     // and require separate dependency management.
     const CG::CGTYPE Type = Handler.getType();
-    event Event;
+    event Event = detail::createSyclObjFromImpl<event>(
+        std::make_shared<detail::event_impl>());
 
     if (PostProcess) {
       bool IsKernel = Type == CG::Kernel;

sycl/source/detail/scheduler/commands.cpp

@@ -582,11 +582,12 @@ Command *Command::processDepEvent(EventImplPtr DepEvent, const DepDesc &Dep,
   const ContextImplPtr &WorkerContext = WorkerQueue->getContextImplPtr();
 
   // 1. Async work is not supported for host device.
-  // 2. Some types of commands do not produce PI events after they are enqueued
-  // (e.g. alloca). Note that we can't check the pi event to make that
-  // distinction since the command might still be unenqueued at this point.
-  bool PiEventExpected =
-      !DepEvent->is_host() || getType() == CommandType::HOST_TASK;
+  // 2. Non-host events can be ignored if they are not fully initialized.
+  // 3. Some types of commands do not produce PI events after they are enqueued
+  //    (e.g. alloca). Note that we can't check the pi event to make that
+  //    distinction since the command might still be unenqueued at this point.
+  bool PiEventExpected = (!DepEvent->is_host() && DepEvent->isInitialized()) ||
+                         getType() == CommandType::HOST_TASK;
   if (auto *DepCmd = static_cast<Command *>(DepEvent->getCommand()))
     PiEventExpected &= DepCmd->producesPiEvent();