Improve performance of dpnp.matmul and dpnp.dot with out keyword (

IntelPython#1694)

* use out keyword for result

* fix strided or overlapping out

* address comments

* fix typo

* remove additional check

dpnp/dpnp_iface.py

@@ -495,17 +495,20 @@ def get_result_array(a, out=None, casting="safe"):
     if out is None:
         return a
     else:
-        dpnp.check_supported_arrays_type(out)
-        if out.shape != a.shape:
-            raise ValueError(
-                f"Output array of shape {a.shape} is needed, got {out.shape}."
-            )
-        elif isinstance(out, dpt.usm_ndarray):
-            out = dpnp_array._create_from_usm_ndarray(out)
+        if a is out:
+            return out
+        else:
+            dpnp.check_supported_arrays_type(out)
+            if out.shape != a.shape:
+                raise ValueError(
+                    f"Output array of shape {a.shape} is needed, got {out.shape}."
+                )
+            elif isinstance(out, dpt.usm_ndarray):
+                out = dpnp_array._create_from_usm_ndarray(out)
 
-        dpnp.copyto(out, a, casting=casting)
+            dpnp.copyto(out, a, casting=casting)
 
-        return out
+            return out
 
 
 def get_usm_ndarray(a):

dpnp/dpnp_utils/dpnp_utils_linearalgebra.py

@@ -36,6 +36,41 @@
 __all__ = ["dpnp_dot", "dpnp_matmul"]
 
 
+def _create_result_array(x1, x2, out, shape, dtype, usm_type, sycl_queue):
+    """
+    Create the result array.
+
+    If `out` is not ``None`` and its features match the specified `shape`, `dtype,
+    `usm_type`, and `sycl_queue` and it is C-contiguous or F-contiguous and
+    does not have any memory overlap with `x1` and `x2`, `out` itself is returned.
+    If these conditions are not statisfied, an empty array is returned with the
+    specified `shape`, `dtype, `usm_type`, and `sycl_queue`.
+    """
+
+    if out is not None:
+        x1_usm = dpnp.get_usm_ndarray(x1)
+        x2_usm = dpnp.get_usm_ndarray(x2)
+        out_usm = dpnp.get_usm_ndarray(out)
+
+        if (
+            out.dtype == dtype
+            and out.shape == shape
+            and out.usm_type == usm_type
+            and out.sycl_queue == sycl_queue
+            and (out.flags.c_contiguous or out.flags.f_contiguous)
+            and not ti._array_overlap(x1_usm, out_usm)
+            and not ti._array_overlap(x2_usm, out_usm)
+        ):
+            return out
+
+    return dpnp.empty(
+        shape,
+        dtype=dtype,
+        usm_type=usm_type,
+        sycl_queue=sycl_queue,
+    )
+
+
 def _copy_array(x, dep_events, host_events, contig_copy=False, dtype=None):
     """
     Creating a copy of input array if needed.
@@ -214,14 +249,9 @@ def dpnp_dot(a, b, /, out=None, *, conjugate=False):
         a, b, dtype=None, casting="no", sycl_queue=exec_q
     )
 
-    # create result array
-    result = dpnp.empty(
-        (),
-        dtype=dot_dtype,
-        usm_type=res_usm_type,
-        sycl_queue=exec_q,
+    result = _create_result_array(
+        a, b, out, (), dot_dtype, res_usm_type, exec_q
     )
-
     # input arrays should have the proper data type
     dep_events_list = []
     host_tasks_list = []
@@ -367,13 +397,10 @@ def dpnp_matmul(
         x2_shape = x2.shape
         res_shape = tuple(tmp_shape) + (x1_shape[-2], x2_shape[-1])
 
-    # calculate results
-    result = dpnp.empty(
-        res_shape,
-        dtype=gemm_dtype,
-        usm_type=res_usm_type,
-        sycl_queue=exec_q,
+    result = _create_result_array(
+        x1, x2, out, res_shape, gemm_dtype, res_usm_type, exec_q
     )
+    # calculate result
     if result.size == 0:
         pass
     elif x1.size == 0 or x2.size == 0: