pytato: Convert einsum arg_names into PrefixNamed tags

Author: inducer

arraycontext/impl/pytato/__init__.py

@@ -219,19 +219,33 @@ def tag_axis(self, iaxis, tags: Union[Sequence[Tag], Tag], array):
     def einsum(self, spec, *args, arg_names=None, tagged=()):
         import pyopencl.array as cla
         import pytato as pt
-        if arg_names is not None:
-            from warnings import warn
-            warn("'arg_names' don't bear any significance in "
-                 "PytatoPyOpenCLArrayContext.", stacklevel=2)
+        if arg_names is None:
+            arg_names = (None,) * len(args)
 
-        def preprocess_arg(arg):
+        def preprocess_arg(name, arg):
             if isinstance(arg, cla.Array):
-                return self.thaw(arg)
+                ary = self.thaw(arg)
             else:
                 assert isinstance(arg, pt.Array)
-                return arg
+                ary = arg
 
-        return pt.einsum(spec, *(preprocess_arg(arg) for arg in args))
+            if name is not None:
+                from pytato.tags import PrefixNamed
+
+                # Tagging Placeholders with naming-related tags is pointless:
+                # They already have names. It's also counterproductive, as
+                # multiple placeholders with the same name that are not
+                # also the same object are not allowed, and this would produce
+                # a different Placeholder object of the same name.
+                if not isinstance(ary, pt.Placeholder):
+                    ary = ary.tagged(PrefixNamed(name))
+
+            return ary
+
+        return pt.einsum(spec, *[
+            preprocess_arg(name, arg)
+            for name, arg in zip(arg_names, args)
+            ])
 
     @property
     def permits_inplace_modification(self):