Make if_positive keep strides of then_ if known. (#523)

* Make if_positive keep strides of then_ if known.

The previous version of `if_positive` always returns a C-ordered array even if `then_` is not C-ordered. This breaks artificial viscosity in Mirgecom when an array context uses a Fortran style data layout. This change makes the output have the same strides as `then_` if the shape of `then_` is known, otherwise it defaults to use the same layout as `criterion`.

* Increment version

* Resolve Flake8 failures

* Use more idiomatic != in shape comparison

Co-authored-by: Andreas Klöckner <[email protected]>

Author: nchristensen

pyopencl/array.py

@@ -2863,9 +2863,19 @@ def if_positive(criterion, then_, else_, out=None, queue=None):
         raise AssertionError()
 
     if out is None:
-        out = empty(
-                criterion.queue, criterion.shape, then_.dtype,
-                allocator=criterion.allocator)
+
+        if then_.shape != ():
+            out = empty_like(
+                then_, criterion.queue, allocator=criterion.allocator)
+        else:
+            # Use same strides as criterion
+            cr_byte_strides = np.array(criterion.strides, dtype=np.int64)
+            cr_item_strides = cr_byte_strides // criterion.dtype.itemsize
+            out_strides = tuple(cr_item_strides*then_.dtype.itemsize)
+
+            out = Array(criterion.queue, criterion.shape, then_.dtype,
+                        allocator=criterion.allocator,
+                        strides=out_strides)
 
     event1 = _if_positive(out, criterion, then_, else_, queue=queue)
     out.add_event(event1)

pyopencl/version.py

@@ -1,3 +1,3 @@
-VERSION = (2021, 2, 9)
+VERSION = (2021, 2, 10)
 VERSION_STATUS = ""
 VERSION_TEXT = ".".join(str(x) for x in VERSION) + VERSION_STATUS