Small slate fix (#3811)

* Fix entrypoint logic in SLATE

firedrake/slate/slac/utils.py

@@ -247,13 +247,17 @@ def merge_loopy(slate_loopy, output_arg, builder, var2terminal, name):
 
     for tsfc_loopy in tsfc_kernels:
         slate_wrapper = merge([slate_wrapper, tsfc_loopy])
-        names = tsfc_loopy.callables_table
-        for name in names:
+    slate_wrapper = merge([slate_wrapper, slate_loopy])
+
+    # At this point the individual subkernels are no longer callable, we
+    # only want to access the generated code via the wrapper.
+    slate_wrapper = slate_wrapper.with_entrypoints({name})
+
+    for tsfc_loopy in tsfc_kernels:
+        for name in tsfc_loopy.callables_table:
             if isinstance(slate_wrapper.callables_table[name], CallableKernel):
                 slate_wrapper = _match_caller_callee_argument_dimension_(slate_wrapper, name)
-    slate_wrapper = merge([slate_wrapper, slate_loopy])
-    names = slate_loopy.callables_table
-    for name in names:
+    for name in slate_loopy.callables_table:
         if isinstance(slate_wrapper.callables_table[name], CallableKernel):
             slate_wrapper = _match_caller_callee_argument_dimension_(slate_wrapper, name)