[PATCH] D106426: [FuncSpec] Support specialising recursive functions

[Chuanqi Xu via Phabricator via llvm-commits]

ChuanqiXu added a comment.

In D106426#2903857 <https://reviews.llvm.org/D106426#2903857>, @SjoerdMeijer wrote:

> I am looking into this now, but now that we have cleared up the problem in previous messages, a.k.a are on the same page how things work for recursive function, I think we need to discuss how the cost-model changes would look like. Because in this example the numbers are arbitrary and a rationale is missing:
>
>> I guess I would be happy if recursiveFunc  would get specialized less than 4 times even when we set  func-specialization-max-iters to 100.
>
> Why 4 times? In other words, what is the metric here? Is that code-size or something else?

4 times is an arbitrary number. I thought the best would be 1 time only. But I worried if it is too strict. So I said 4 times. Now I think we should be more strict. So I think it would better to specialize it only 1 time.

> how things work for recursive function, I think we need to discuss how the cost-model changes would look like

I think we need to handle recursive function specially. Since it is common that recursive function f  and its specialized one f' have the same cost and bonus. We need to record the function specialized (and specialized argument). Then we need to specialize a function (for specific argument) we had specialized, we could forbid it or give it a much higher penalty. The detail is missing. But the key point is that we need to handle recursive function specially instead of tuning or refactoring the cost model.


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