add a CL device<->host transfer mapper

pytato/transform/__init__.py

@@ -1951,4 +1951,52 @@ def cached_data_wrapper_if_present(ary: ArrayOrNames) -> ArrayOrNames:
 
 # }}}
 
+
+# {{{ TransferMapper
+
+class TransferMapper(CopyMapper):
+    def __init__(self, to_device: bool, queue: Any, allocator: Any = None) -> None:
+        super().__init__()
+        self.to_device = to_device
+        self.queue = queue
+        self.allocator = allocator
+
+    def map_data_wrapper(self, expr: DataWrapper) -> Array:
+        import sys
+        if "pyopencl" not in sys.modules:
+            return super().map_data_wrapper(expr)
+
+        from pyopencl.array import Array as CLArray, to_device
+
+        if isinstance(expr.data, CLArray) and not self.to_device:
+            data = expr.data.get()
+            return DataWrapper(
+                data=data,
+                shape=expr.shape,
+                axes=expr.axes,
+                tags=expr.tags,
+                non_equality_tags=expr.non_equality_tags)
+        elif isinstance(expr.data, np.ndarray) and self.to_device:
+            data = to_device(self.queue, expr.data, allocator=self.allocator)
+            return DataWrapper(
+                data=data,
+                shape=expr.shape,
+                axes=expr.axes,
+                tags=expr.tags,
+                non_equality_tags=expr.non_equality_tags)
+
+        return super().map_data_wrapper(expr)
+
+
+def transfer_to_device(expr: ArrayOrNames, queue: Any,
+                       allocator: Any = None) -> ArrayOrNames:
+    return TransferMapper(True, queue, allocator)(expr)
+
+
+def transfer_to_host(expr: ArrayOrNames, queue: Any,
+                     allocator: Any = None) -> ArrayOrNames:
+    return TransferMapper(False, queue, allocator)(expr)
+
+# }}}
+
 # vim: foldmethod=marker