[backport] Fix ravel for strides 0

[chainer-ci]

Backport of #5978 by @emcastillo

[chainer-ci]

[automatic post] Jenkins, test this please.

[chainer-ci]

Jenkins CI test (for commit 5d37283, target branch v9) succeeded!

[toslunar]

pfn-public-ci/cupy.experimental.win.cuda100

The failure seems unrelated to the change. with tempfile.TemporaryDirectory() as root_dir failed on exit. 🤔
https://storage.googleapis.com/chainer-artifacts-pfn-public-ci/cupy-ci/83460/cupy_test_log.txt

================================== FAILURES ===================================
_ TestCubReduction.test_cub_sum[_param_10_{backend='block', order='C', shape=(10, 20, 30)}] _

self = <<cupy_tests.math_tests.test_sumprod.TestCubReduction object at 0x000001F11F4AE198>  parameter: {'backend': 'block', 'order': 'C', 'shape': (10, 20, 30)}>
xp = <module 'cupy' from 'C:\\Development\\Python\\Python37\\lib\\site-packages\\cupy\\__init__.py'>
dtype = <class 'numpy.float64'>, axis = (1, 2)

    @testing.for_contiguous_axes()
    # sum supports less dtypes; don't test float16 as it's not as accurate?
    @testing.for_dtypes('qQfdFD')
    @testing.numpy_cupy_allclose(rtol=1E-5)
    def test_cub_sum(self, xp, dtype, axis):
        a = testing.shaped_random(self.shape, xp, dtype)
        if self.order in ('c', 'C'):
            a = xp.ascontiguousarray(a)
        elif self.order in ('f', 'F'):
            a = xp.asfortranarray(a)
    
        if xp is numpy:
            return a.sum(axis=axis)
    
        # xp is cupy, first ensure we really use CUB
        ret = cupy.empty(())  # Cython checks return type, need to fool it
        if self.backend == 'device':
            func_name = 'cupy._core._routines_math.cub.'
            if len(axis) == len(self.shape):
                func_name += 'device_reduce'
            else:
                func_name += 'device_segmented_reduce'
            with testing.AssertFunctionIsCalled(func_name, return_value=ret):
                a.sum(axis=axis)
        elif self.backend == 'block':
            # this is the only function we can mock; the rest is cdef'd
            func_name = 'cupy._core._cub_reduction.'
            func_name += '_SimpleCubReductionKernel_get_cached_function'
            func = _cub_reduction._SimpleCubReductionKernel_get_cached_function
            if len(axis) == len(self.shape):
                times_called = 2  # two passes
            else:
                times_called = 1  # one pass
            with testing.AssertFunctionIsCalled(
                    func_name, wraps=func, times_called=times_called):
>               a.sum(axis=axis)

cupy_tests\math_tests\test_sumprod.py:266: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
cupy\_core\core.pyx:953: in cupy._core.core.ndarray.sum
    ???
cupy\_core\core.pyx:961: in cupy._core.core.ndarray.sum
    ???
cupy\_core\_routines_math.pyx:118: in cupy._core._routines_math._ndarray_sum
    ???
cupy\_core\_reduction.pyx:564: in cupy._core._reduction._SimpleReductionKernel.__call__
    ???
cupy\_core\_reduction.pyx:349: in cupy._core._reduction._AbstractReductionKernel._call
    ???
cupy\_core\_cub_reduction.pyx:700: in cupy._core._cub_reduction._try_to_call_cub_reduction
    ???
cupy\_core\_cub_reduction.pyx:550: in cupy._core._cub_reduction._launch_cub
    ???
C:\Development\Python\Python37\lib\unittest\mock.py:951: in __call__
    return _mock_self._mock_call(*args, **kwargs)
C:\Development\Python\Python37\lib\unittest\mock.py:1026: in _mock_call
    return self._mock_wraps(*args, **kwargs)
cupy\_util.pyx:59: in cupy._util.memoize.decorator.ret
    ???
cupy\_core\_cub_reduction.pyx:243: in cupy._core._cub_reduction._SimpleCubReductionKernel_get_cached_function
    ???
cupy\_core\_cub_reduction.pyx:228: in cupy._core._cub_reduction._create_cub_reduction_function
    ???
cupy\_core\core.pyx:2043: in cupy._core.core.compile_with_cache
    ???
C:\Development\Python\Python37\lib\site-packages\cupy\cuda\compiler.py:463: in compile_with_cache
    cache_in_memory, jitify)
C:\Development\Python\Python37\lib\site-packages\cupy\cuda\compiler.py:556: in _compile_with_cache_cuda
    log_stream=log_stream)
C:\Development\Python\Python37\lib\site-packages\cupy\cuda\compiler.py:391: in compile_using_nvcc
    assert False, code_type
C:\Development\Python\Python37\lib\tempfile.py:805: in __exit__
    self.cleanup()
C:\Development\Python\Python37\lib\tempfile.py:809: in cleanup
    _shutil.rmtree(self.name)
C:\Development\Python\Python37\lib\shutil.py:513: in rmtree
    return _rmtree_unsafe(path, onerror)
C:\Development\Python\Python37\lib\shutil.py:401: in _rmtree_unsafe
    onerror(os.rmdir, path, sys.exc_info())
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

path = 'C:\\Windows\\TEMP\\flexci\\run-00170418\\tmp\\tmp1yexlmce'
onerror = <function rmtree.<locals>.onerror at 0x000001F1C24FC268>

    def _rmtree_unsafe(path, onerror):
        try:
            with os.scandir(path) as scandir_it:
                entries = list(scandir_it)
        except OSError:
            onerror(os.scandir, path, sys.exc_info())
            entries = []
        for entry in entries:
            fullname = entry.path
            try:
                is_dir = entry.is_dir(follow_symlinks=False)
            except OSError:
                is_dir = False
            if is_dir:
                try:
                    if entry.is_symlink():
                        # This can only happen if someone replaces
                        # a directory with a symlink after the call to
                        # os.scandir or entry.is_dir above.
                        raise OSError("Cannot call rmtree on a symbolic link")
                except OSError:
                    onerror(os.path.islink, fullname, sys.exc_info())
                    continue
                _rmtree_unsafe(fullname, onerror)
            else:
                try:
                    os.unlink(fullname)
                except OSError:
                    onerror(os.unlink, fullname, sys.exc_info())
        try:
>           os.rmdir(path)
E           AssertionError: Only cupy raises error
E           
E           Traceback (most recent call last):
E             File "C:\Development\Python\Python37\lib\site-packages\cupy\testing\_helper.py", line 47, in _call_func
E               result = impl(*args, **kw)
E             File "C:\Windows\TEMP\flexci\run-00170418\work\src\tests\cupy_tests\math_tests\test_sumprod.py", line 266, in test_cub_sum
E               a.sum(axis=axis)
E             File "cupy\_core\core.pyx", line 953, in cupy._core.core.ndarray.sum
E             File "cupy\_core\core.pyx", line 961, in cupy._core.core.ndarray.sum
E             File "cupy\_core\_routines_math.pyx", line 118, in cupy._core._routines_math._ndarray_sum
E             File "cupy\_core\_reduction.pyx", line 564, in cupy._core._reduction._SimpleReductionKernel.__call__
E             File "cupy\_core\_reduction.pyx", line 349, in cupy._core._reduction._AbstractReductionKernel._call
E             File "cupy\_core\_cub_reduction.pyx", line 700, in cupy._core._cub_reduction._try_to_call_cub_reduction
E             File "cupy\_core\_cub_reduction.pyx", line 550, in cupy._core._cub_reduction._launch_cub
E             File "C:\Development\Python\Python37\lib\unittest\mock.py", line 951, in __call__
E               return _mock_self._mock_call(*args, **kwargs)
E             File "C:\Development\Python\Python37\lib\unittest\mock.py", line 1026, in _mock_call
E               return self._mock_wraps(*args, **kwargs)
E             File "cupy\_util.pyx", line 59, in cupy._util.memoize.decorator.ret
E             File "cupy\_core\_cub_reduction.pyx", line 243, in cupy._core._cub_reduction._SimpleCubReductionKernel_get_cached_function
E             File "cupy\_core\_cub_reduction.pyx", line 228, in cupy._core._cub_reduction._create_cub_reduction_function
E             File "cupy\_core\core.pyx", line 2043, in cupy._core.core.compile_with_cache
E             File "C:\Development\Python\Python37\lib\site-packages\cupy\cuda\compiler.py", line 463, in compile_with_cache
E               cache_in_memory, jitify)
E             File "C:\Development\Python\Python37\lib\site-packages\cupy\cuda\compiler.py", line 556, in _compile_with_cache_cuda
E               log_stream=log_stream)
E             File "C:\Development\Python\Python37\lib\site-packages\cupy\cuda\compiler.py", line 391, in compile_using_nvcc
E               assert False, code_type
E             File "C:\Development\Python\Python37\lib\tempfile.py", line 805, in __exit__
E               self.cleanup()
E             File "C:\Development\Python\Python37\lib\tempfile.py", line 809, in cleanup
E               _shutil.rmtree(self.name)
E             File "C:\Development\Python\Python37\lib\shutil.py", line 513, in rmtree
E               return _rmtree_unsafe(path, onerror)
E             File "C:\Development\Python\Python37\lib\shutil.py", line 401, in _rmtree_unsafe
E               onerror(os.rmdir, path, sys.exc_info())
E             File "C:\Development\Python\Python37\lib\shutil.py", line 399, in _rmtree_unsafe
E               os.rmdir(path)
E           OSError: [WinError 145] The directory is not empty: 'C:\\Windows\\TEMP\\flexci\\run-00170418\\tmp\\tmp1yexlmce'

C:\Development\Python\Python37\lib\shutil.py:399: AssertionError
---------------------------- Captured stdout call -----------------------------
dtype is d
axis is (1, 2) , ndim is 3 , shape is (10, 20, 30) , order is C

[emcastillo]

Jenkins, test this please

[chainer-ci]

Jenkins CI test (for commit 5d37283, target branch v9) failed with status FAILURE.

[emcastillo]

Jenkins failures unrelated