You can't. Type inference for instruction selection requires that the
final types in a pattern are exact (i.e. that it infers a single type
for each node in the pattern), regardless of the output pattern. Since
GR32 allows multiple types, you need to specify the two input patterns
I think we can make table gen generate pattern with complete type
information (when type is not specify for some input/output parameter) so
that code is less. I am not sure apart from me anyone want such feature.
But if it is good to have then I can look into it.