[SYCL] Initialize uninitialized handler_impl fields (#15323)

In the same vein as #15237, this PR
fixes additional uninitialized values recently discovered by Coverity.
Similar to the resolution discussed in #15237, I have
default-initialized integer values that are defined later on to 0
instead of another more complex solution.

Additionally, since I had set `MExternalSempahore` in `handler_impl` to
`nullptr`, I added null checks where `MExternalSemaphore` is ultimately
returned to ensure `nullptr` doesn't actually get passed into the UR.
This is not necessarily necessary, but without this check Coverity would
probably generate another hit because of it.

sycl/source/detail/cg.hpp

@@ -624,6 +624,8 @@ class CGSemaphoreWait : public CG {
  MExternalSemaphore(ExternalSemaphore), MWaitValue(WaitValue) {}
 
  ur_exp_external_semaphore_handle_t getExternalSemaphore() const {
+ assert(MExternalSemaphore != nullptr &&
+ "MExternalSemaphore has not been defined yet.");
  return MExternalSemaphore;
  }
  std::optional<uint64_t> getWaitValue() const { return MWaitValue; }
@@ -643,6 +645,10 @@ class CGSemaphoreSignal : public CG {
  MExternalSemaphore(ExternalSemaphore), MSignalValue(SignalValue) {}
 
  ur_exp_external_semaphore_handle_t getExternalSemaphore() const {
+ if (MExternalSemaphore == nullptr)
+ throw exception(make_error_code(errc::runtime),
+ "getExternalSemaphore(): MExternalSemaphore has not been "
+ "defined yet.");
  return MExternalSemaphore;
  }
  std::optional<uint64_t> getSignalValue() const { return MSignalValue; }

sycl/source/detail/handler_impl.hpp

@@ -90,13 +90,13 @@ class handler_impl {
 
  std::shared_ptr<detail::kernel_bundle_impl> MKernelBundle;
 
- ur_usm_advice_flags_t MAdvice;
+ ur_usm_advice_flags_t MAdvice = 0;
 
  // 2D memory operation information.
- size_t MSrcPitch;
- size_t MDstPitch;
- size_t MWidth;
- size_t MHeight;
+ size_t MSrcPitch = 0;
+ size_t MDstPitch = 0;
+ size_t MWidth = 0;
+ size_t MHeight = 0;
 
  /// Offset into a device_global for copy operations.
  size_t MOffset = 0;
@@ -134,7 +134,7 @@ class handler_impl {
  ur_rect_region_t MCopyExtent = {};
 
  // Extra information for semaphore interoperability
- ur_exp_external_semaphore_handle_t MExternalSemaphore;
+ ur_exp_external_semaphore_handle_t MExternalSemaphore = nullptr;
  std::optional<uint64_t> MWaitValue;
  std::optional<uint64_t> MSignalValue;