-Wsometimes-uninitialized thrown when building _sycl_queue extension

[diptorupd]

I am seeing the following warning when building _sycl_queue extension.

[104/112] Building CXX object dpctl/CMakeFiles/_sycl_queue.dir/_sycl_queue.cxx.o
/home/diptorupd/Desktop/devel/dpctl/_skbuild/linux-x86_64-3.9/cmake-build/dpctl/_sycl_queue.cxx:4564:3: warning: variable '__pyx_gilstate_save' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
  __Pyx_TraceLine(125,1,__PYX_ERR(0, 125, __pyx_L1_error))
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/diptorupd/Desktop/devel/dpctl/_skbuild/linux-x86_64-3.9/cmake-build/dpctl/_sycl_queue.cxx:2003:19: note: expanded from macro '__Pyx_TraceLine'
              if (unlikely(ret)) goto_error;\
                  ^~~~~~~~~~~~~
/home/diptorupd/Desktop/devel/dpctl/_skbuild/linux-x86_64-3.9/cmake-build/dpctl/_sycl_queue.cxx:842:23: note: expanded from macro 'unlikely'
  #define unlikely(x) __builtin_expect(!!(x), 0)
                      ^~~~~~~~~~~~~~~~~~~~~~~~~~
/home/diptorupd/Desktop/devel/dpctl/_skbuild/linux-x86_64-3.9/cmake-build/dpctl/_sycl_queue.cxx:4634:28: note: uninitialized use occurs here
  __Pyx_PyGILState_Release(__pyx_gilstate_save);
                           ^~~~~~~~~~~~~~~~~~~
/home/diptorupd/Desktop/devel/dpctl/_skbuild/linux-x86_64-3.9/cmake-build/dpctl/_sycl_queue.cxx:4564:3: note: remove the 'if' if its condition is always false
  __Pyx_TraceLine(125,1,__PYX_ERR(0, 125, __pyx_L1_error))
  ^
/home/diptorupd/Desktop/devel/dpctl/_skbuild/linux-x86_64-3.9/cmake-build/dpctl/_sycl_queue.cxx:2003:15: note: expanded from macro '__Pyx_TraceLine'
              if (unlikely(ret)) goto_error;\
              ^
/home/diptorupd/Desktop/devel/dpctl/_skbuild/linux-x86_64-3.9/cmake-build/dpctl/_sycl_queue.cxx:4555:3: warning: variable '__pyx_gilstate_save' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
  __Pyx_TraceCall("default_async_error_handler", __pyx_f[0], 124, 1, __PYX_ERR(0, 124, __pyx_L1_error));
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/diptorupd/Desktop/devel/dpctl/_skbuild/linux-x86_64-3.9/cmake-build/dpctl/_sycl_queue.cxx:1881:15: note: expanded from macro '__Pyx_TraceCall'
          if (unlikely(__Pyx_use_tracing < 0)) goto_error;\
              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/diptorupd/Desktop/devel/dpctl/_skbuild/linux-x86_64-3.9/cmake-build/dpctl/_sycl_queue.cxx:842:23: note: expanded from macro 'unlikely'
  #define unlikely(x) __builtin_expect(!!(x), 0)
                      ^~~~~~~~~~~~~~~~~~~~~~~~~~
/home/diptorupd/Desktop/devel/dpctl/_skbuild/linux-x86_64-3.9/cmake-build/dpctl/_sycl_queue.cxx:4634:28: note: uninitialized use occurs here
  __Pyx_PyGILState_Release(__pyx_gilstate_save);
                           ^~~~~~~~~~~~~~~~~~~
/home/diptorupd/Desktop/devel/dpctl/_skbuild/linux-x86_64-3.9/cmake-build/dpctl/_sycl_queue.cxx:4555:3: note: remove the 'if' if its condition is always false
  __Pyx_TraceCall("default_async_error_handler", __pyx_f[0], 124, 1, __PYX_ERR(0, 124, __pyx_L1_error));
  ^
/home/diptorupd/Desktop/devel/dpctl/_skbuild/linux-x86_64-3.9/cmake-build/dpctl/_sycl_queue.cxx:1881:11: note: expanded from macro '__Pyx_TraceCall'
          if (unlikely(__Pyx_use_tracing < 0)) goto_error;\
          ^
/home/diptorupd/Desktop/devel/dpctl/_skbuild/linux-x86_64-3.9/cmake-build/dpctl/_sycl_queue.cxx:4552:3: note: variable '__pyx_gilstate_save' is declared here
  PyGILState_STATE __pyx_gilstate_save;

[oleksandr-pavlyk]

This only comes up when building with coverage for me. It is happening for default_asynch_handler function, which is

cdef class SyclAsynchronousError(Exception):
    """
    A SyclAsynchronousError exception is raised when SYCL operation submission
    or execution encounters an error.
    """

cdef void default_async_error_handler(int err) nogil except *:
    with gil:
        raise SyclAsynchronousError(err)

Perhaps a small Cython reproducer is needed to further understand and triage the issue.

[oleksandr-pavlyk]

Reproducer: https://github.com/oleksandr-pavlyk/compiler-warning-cython-generated-source-reproducer

The trigger is the use of CYTHON_TRACE_NOGIL=1. We switched to setting it with transition to scikit-build.

I will file a separate report for Cython developers to look at.

[oleksandr-pavlyk]

The issue appears to be fixed in Cython 3.0.0 trunk. Issue cython/cython#4637 filed upstream.

[oleksandr-pavlyk]

We can fix the issue by using alpha releases of Cython 3.0 in generate-coverage workflow, or by disabling coverage collection of NOGIL code.

I would prefer using Cython=3.0. This would also ensure dpctl Cython code works with development version of Cython.

@diptorupd

[diptorupd]

I would prefer using Cython=3.0. This would also ensure dpctl Cython code works with development version of Cython.

Let us do it.

[oleksandr-pavlyk]

This will be fixed in Cython 0.29.29: cython/cython#4703

[oleksandr-pavlyk]

The fix was reverted in 0.29.30 due to causing a show-stopper.

[oleksandr-pavlyk]

This has been fixed in Cython 3.0, and this issue has been resolved by gh-1302 with dpctl's transition to Cython 3.0