memoize of functions with updates consuming input buffers is not possible?

[dsharletg]

I haven't been able to figure out how to use memoize on a function with an update stage that consumes an input.

For example:

Func sum_input;
sum_input() += input(r.x, r.y);

I have tried various combinations of memoize and memoize_tag on this func without success:

• memoize is only possible on Func, not Stage
• It's unclear how to use memoize_tag to resolve the error about using an input buffer when memoized. I've tried wrapping input(r.x, r.y), and I've tried adding a pure definition sum_input() = 0 and wrapping 0 with memoize_tag.