Clean up __cuda_array_interface__ handling in as_column (#15477)

Removes some unnecessary type cast checking and NaT handling as cupy does not support datelike types cupy/cupy#2622

Authors:
  - Matthew Roeschke (https://github.com/mroeschke)

Approvers:
  - Vyas Ramasubramani (https://github.com/vyasr)

URL: #15477

python/cudf/cudf/core/column/column.py

@@ -1679,27 +1679,6 @@ def build_categorical_column(
     return cast("cudf.core.column.CategoricalColumn", result)
 
 
-def _make_copy_replacing_NaT_with_null(column):
-    """Return a copy with NaT values replaced with nulls."""
-    if np.issubdtype(column.dtype, np.timedelta64):
-        na_value = np.timedelta64("NaT", column.time_unit)
-    elif np.issubdtype(column.dtype, np.datetime64):
-        na_value = np.datetime64("NaT", column.time_unit)
-    else:
-        raise ValueError("This type does not support replacing NaT with null.")
-
-    null = column_empty_like(column, masked=True, newsize=1)
-    out_col = cudf._lib.replace.replace(
-        column,
-        build_column(
-            as_buffer(np.array([na_value], dtype=column.dtype).view("|u1")),
-            dtype=column.dtype,
-        ),
-        null,
-    )
-    return out_col
-
-
 def check_invalid_array(shape: tuple, dtype):
     """Invalid ndarrays properties that are not supported"""
     if len(shape) > 1:
@@ -1782,50 +1761,30 @@ def as_column(
         return arbitrary
     elif hasattr(arbitrary, "__cuda_array_interface__"):
         desc = arbitrary.__cuda_array_interface__
-        shape = desc["shape"]
-        current_dtype = np.dtype(desc["typestr"])
-
-        check_invalid_array(shape, current_dtype)
-
-        arb_dtype = cudf.dtype(current_dtype)
+        check_invalid_array(desc["shape"], np.dtype(desc["typestr"]))
 
         if desc.get("mask", None) is not None:
             # Extract and remove the mask from arbitrary before
             # passing to cupy.asarray
-            mask = _mask_from_cuda_array_interface_desc(arbitrary)
-            arbitrary = SimpleNamespace(__cuda_array_interface__=desc.copy())
-            arbitrary.__cuda_array_interface__["mask"] = None
-            desc = arbitrary.__cuda_array_interface__
+            cai_copy = desc.copy()
+            mask = _mask_from_cuda_array_interface_desc(
+                arbitrary, cai_copy.pop("mask")
+            )
+            arbitrary = SimpleNamespace(__cuda_array_interface__=cai_copy)
         else:
             mask = None
 
         arbitrary = cupy.asarray(arbitrary)
-
-        if arb_dtype != current_dtype:
-            arbitrary = arbitrary.astype(arb_dtype)
-            current_dtype = arb_dtype
-
-        if (
-            desc["strides"] is not None
-            and not (arbitrary.itemsize,) == arbitrary.strides
-        ):
-            arbitrary = cupy.ascontiguousarray(arbitrary)
+        arbitrary = cupy.ascontiguousarray(arbitrary)
 
         data = as_buffer(arbitrary, exposed=cudf.get_option("copy_on_write"))
-        col = build_column(data, dtype=current_dtype, mask=mask)
-
+        col = build_column(data, dtype=arbitrary.dtype, mask=mask)
+        if (
+            nan_as_null or (mask is None and nan_as_null is None)
+        ) and col.dtype.kind == "f":
+            col = col.nans_to_nulls()
         if dtype is not None:
             col = col.astype(dtype)
-
-        if isinstance(col, cudf.core.column.CategoricalColumn):
-            return col
-        elif np.issubdtype(col.dtype, np.floating):
-            if nan_as_null or (mask is None and nan_as_null is None):
-                mask = libcudf.transform.nans_to_nulls(col.fillna(np.nan))
-                col = col.set_mask(mask)
-        elif np.issubdtype(col.dtype, np.datetime64):
-            if nan_as_null or (mask is None and nan_as_null is None):
-                col = _make_copy_replacing_NaT_with_null(col)
         return col
 
     elif isinstance(arbitrary, (pa.Array, pa.ChunkedArray)):
@@ -2222,27 +2181,18 @@ def as_column(
         return as_column(arbitrary, nan_as_null=nan_as_null, dtype=dtype)
 
 
-def _mask_from_cuda_array_interface_desc(obj) -> Union[Buffer, None]:
-    desc = obj.__cuda_array_interface__
-    mask = desc.get("mask", None)
-
-    if mask is not None:
-        desc = mask.__cuda_array_interface__
-        ptr = desc["data"][0]
-        nelem = desc["shape"][0]
-        typestr = desc["typestr"]
-        typecode = typestr[1]
-        if typecode == "t":
-            mask_size = bitmask_allocation_size_bytes(nelem)
-            mask = as_buffer(data=ptr, size=mask_size, owner=obj)
-        elif typecode == "b":
-            col = as_column(mask)
-            mask = bools_to_mask(col)
-        else:
-            raise NotImplementedError(
-                f"Cannot infer mask from typestr {typestr}"
-            )
-    return mask
+def _mask_from_cuda_array_interface_desc(obj, cai_mask) -> Buffer:
+    desc = cai_mask.__cuda_array_interface__
+    typestr = desc["typestr"]
+    typecode = typestr[1]
+    if typecode == "t":
+        mask_size = bitmask_allocation_size_bytes(desc["shape"][0])
+        return as_buffer(data=desc["data"][0], size=mask_size, owner=obj)
+    elif typecode == "b":
+        col = as_column(cai_mask)
+        return bools_to_mask(col)
+    else:
+        raise NotImplementedError(f"Cannot infer mask from typestr {typestr}")
 
 
 def serialize_columns(columns) -> Tuple[List[dict], List]: