Fixes #693

Constructor make more rigorous checks for contiguity flags.

When constructor is checking contiguity of the 1D array, it needs to
account for 1-element array no matter the value of strides[0].

Similarly for higher dimensionality, contiguity check should not
take into account slots with dimensions of 1.

X1 = usm_ndarray((1,3,1), 'i4', 'device', strides=(0,1,0))
X2 = usm_ndarray((2,1,3), 'i4', 'device', strides=(3, 0, 1))
X3 = usm_ndarray((2,1,3), 'i4', 'device', strides=(1, 0, 2))

Author: oleksandr-pavlyk

dpctl/tensor/_stride_utils.pxi

@@ -61,6 +61,7 @@ cdef int _from_input_shape_strides(
         Otherwise they are set to NULL
     """
     cdef int i
+    cdef int j
     cdef int all_incr = 1
     cdef int all_decr = 1
     cdef Py_ssize_t elem_count = 1
@@ -115,6 +116,15 @@ cdef int _from_input_shape_strides(
             contig[0] = USM_ARRAY_C_CONTIGUOUS
         else:
             contig[0] = USM_ARRAY_F_CONTIGUOUS
+        if nd == 1:
+            contig[0] = USM_ARRAY_C_CONTIGUOUS | USM_ARRAY_F_CONTIGUOUS
+        else:
+            j = 0
+            for i in range(nd):
+                if shape_arr[i] > 1:
+                    j = j + 1
+            if j < 2:
+                contig[0] = USM_ARRAY_C_CONTIGUOUS | USM_ARRAY_F_CONTIGUOUS
         min_disp[0] = 0
         max_disp[0] = (elem_count - 1)
         strides_ptr[0] = <Py_ssize_t *>(<size_t>0)
@@ -137,26 +147,42 @@ cdef int _from_input_shape_strides(
         min_disp[0] = min_shift
         max_disp[0] = max_shift
         if max_shift == min_shift + (elem_count - 1):
+            if elem_count == 1:
+                contig[0] = (USM_ARRAY_C_CONTIGUOUS | USM_ARRAY_F_CONTIGUOUS)
+                return 0
             if nd == 1:
                 if strides_arr[0] == 1:
                     contig[0] = USM_ARRAY_C_CONTIGUOUS
                 else:
                     contig[0] = 0
                 return 0
-            for i in range(0, nd - 1):
-                if all_incr:
-                    all_incr = (
-                        (strides_arr[i] > 0) and
-                        (strides_arr[i+1] > 0) and
-                        (strides_arr[i] <= strides_arr[i + 1])
-                    )
-                if all_decr:
-                    all_decr = (
-                        (strides_arr[i] > 0) and
-                        (strides_arr[i+1] > 0) and
-                        (strides_arr[i] >= strides_arr[i + 1])
-                    )
-            if all_incr:
+            i = 0
+            while i < nd:
+                if shape_arr[i] == 1:
+                    i = i + 1
+                    continue
+                j = i + 1
+                while (j < nd and shape_arr[j] == 1):
+                    j = j + 1
+                if j < nd:
+                    if all_incr:
+                        all_incr = (
+                            (strides_arr[i] > 0) and
+                            (strides_arr[j] > 0) and
+                            (strides_arr[i] <= strides_arr[j])
+                        )
+                    if all_decr:
+                        all_decr = (
+                            (strides_arr[i] > 0) and
+                            (strides_arr[j] > 0) and
+                            (strides_arr[i] >= strides_arr[j])
+                        )
+                    i = j
+                else:
+                    break
+            if all_incr and all_decr:
+                contig[0] = (USM_ARRAY_C_CONTIGUOUS | USM_ARRAY_F_CONTIGUOUS)
+            elif all_incr:
                 contig[0] = USM_ARRAY_F_CONTIGUOUS
             elif all_decr:
                 contig[0] = USM_ARRAY_C_CONTIGUOUS

dpctl/tests/test_usm_ndarray_ctor.py

@@ -59,6 +59,16 @@ def test_allocate_usm_ndarray(shape, usm_type):
     assert X.shape == X.__sycl_usm_array_interface__["shape"]
 
 
+def test_usm_ndarray_flags():
+    assert dpt.usm_ndarray((5,)).flags == 3
+    assert dpt.usm_ndarray((5, 2)).flags == 1
+    assert dpt.usm_ndarray((5, 2), order="F").flags == 2
+    assert dpt.usm_ndarray((5, 1, 2), order="F").flags == 2
+    assert dpt.usm_ndarray((5, 1, 2), strides=(2, 0, 1)).flags == 1
+    assert dpt.usm_ndarray((5, 1, 2), strides=(1, 0, 5)).flags == 2
+    assert dpt.usm_ndarray((5, 1, 1), strides=(1, 0, 1)).flags == 3
+
+
 @pytest.mark.parametrize(
     "dtype",
     [
@@ -703,11 +713,10 @@ def relaxed_strides_equal(st1, st2, sh):
         5,
     )
     X = dpt.usm_ndarray(sh_s, dtype="d")
-    expected_flags = X.flags
     X.shape = sh_f
     assert X.shape == sh_f
     assert relaxed_strides_equal(X.strides, cc_strides(sh_f), sh_f)
-    assert X.flags == expected_flags
+    assert X.flags & 1, "reshaped array expected to be C-contiguous"
 
     sh_s = (
         2,
@@ -842,6 +851,10 @@ def test_reshape():
     W = dpt.reshape(Z, (-1,), order="C")
     assert W.shape == (Z.size,)
 
+    X = dpt.usm_ndarray((1,))
+    Y = dpt.reshape(X, X.shape)
+    assert Y.flags == X.flags
+
 
 def test_transpose():
     n, m = 2, 3