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

[Zdenek Dvorak <rakdver at kam dot mff dot cuni dot cz>]

Hi,

> On Wed, Jun 30, 2010 at 7:34 PM, Fang, Changpeng <Changpeng.Fang@amd.com> wrote:
> >> 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.
> 
> It shouldn't take that long.  Can you gather a more detailed profile?

actually, compute_all_dependences is quadratic in the number of memory
references, and in more complicated cases, it can perform rather complex
computations, so 5 seconds on 729 references does seem like a realistic time.
Of course, we need to either speed up the analysis or add an cut-off to avoid
it on loops with too many memory references (or both),

Zdenek