Re: Why doesn’t the simple optimizer fuse casts?

Hi Alexis, Nested casts shouldn't happen. The mkCast function gets rid of them. Someone somewhere is forgetting to call it. If you have a concrete program that leads to nested casts, post a bug report. :) Thanks! Richard

On Apr 27, 2020, at 8:29 PM, Alexis King wrote:

This question is spurred by curiosity more than anything else, but I’ve noticed that the simple optimizer doesn’t fuse nested casts, and I’m wondering if there’s any reason it couldn’t. To make what I’m talking about more concrete, suppose we have an expression like this:

(x |> co) |> sym co

It seems like it would be trivial for simpleOptExpr to fuse the nested casts to get

x |> co; sym co

and then the coercion optimizer could get rid of it entirely. Moreover, this seems within the spirit of the simple optimizer, since it’s really just “cleaning up” an expression. Is there any reason the simple optimizer doesn’t do this, or is it just something nobody implemented?

(For context, I’ve recently been staring at a lot of -ddump-ds output, and there happen to be a bunch of nested casts in the result that are really just noise. It would be nice if the simple optimizer got rid of them for me.)

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