[Patch PR 44576]: Reduce the computation cost in compute_miss_rate for prefetching loop arrays

[Fang, Changpeng]

> FOR_EACH_LOOP (li, loop, LI_ONLY_INNERMOST)

>does that make a difference?

This doesn't help, because "compute_all_dependences" was called the same number of time
as before.

(BTW, should we limit prefetching only to the innermost one?)

In this test case, there are 6 large loops, where each loop has 729 memory reference.
It takes 4~5 seconds to "compute_all_dependence" for one such loop.


> The patch passed Bootstrapping and regression tests.
>
> Is this patch OK to commit?

>Ok.

 Thank you.

Changpeng