restore loop inference fallback

arraycontext/impl/pyopencl/__init__.py

@@ -324,10 +324,33 @@ def transform_loopy_program(self, t_unit):
                     "to create this kernel?")
 
         all_inames = default_entrypoint.all_inames()
-
+        # FIXME: This could be much smarter.
         inner_iname = None
 
-        if "i0" in all_inames:
+        # import with underscore to avoid DeprecationWarning
+        # from arraycontext.metadata import _FirstAxisIsElementsTag
+        from meshmode.transform_metadata import FirstAxisIsElementsTag
+
+        if (len(default_entrypoint.instructions) == 1
+                and isinstance(default_entrypoint.instructions[0], lp.Assignment)
+                and any(isinstance(tag, FirstAxisIsElementsTag)
+                    # FIXME: Firedrake branch lacks kernel tags
+                    for tag in getattr(default_entrypoint, "tags", ()))):
+            stmt, = default_entrypoint.instructions
+
+            out_inames = [v.name for v in stmt.assignee.index_tuple]
+            assert out_inames
+            outer_iname = out_inames[0]
+            if len(out_inames) >= 2:
+                inner_iname = out_inames[1]
+
+        elif "iel" in all_inames:
+            outer_iname = "iel"
+
+            if "idof" in all_inames:
+                inner_iname = "idof"
+
+        elif "i0" in all_inames:
             outer_iname = "i0"
 
             if "i1" in all_inames: