Re: ptrlist-iterator performance on one wine source file

[Christopher Li <sparse@chrisli.org>]

On Fri, Aug 4, 2017 at 6:26 PM, Luc Van Oostenryck
<luc.vanoostenryck@gmail.com> wrote:
>
> I have investigated a little more because even 2.1 or 1.93s seems
> too much to me.

Thanks for looking into this.

>
> My conclusion is that the file is (really too) big (but see the end).
> For example, there is:
> - about 1 million calls to clean_up_one_instruction
> - and 2.6 million calls to  insn_compare()
> OTOH there is only 56000 calls to try_to_cse()
> and these results in 82000 calls to bb_dominates()
> and 29000 calls to cse_one_instruction().
>
> All this indicate that the CSE is rather efficient:
> only 56000 real CSE checks, each calling roughly 3/2
> calls to bb_dominates() and 1/2 calls to cse_one_insn().
>
> And in fact, most of these calls are not even really expensive.
>
> The real offending, taking about 75% of CPU time, is bb_dominates()
> which while only directly called 82000 is a recursive function which
> internally is called more than 71 million of time!
> In other words, the mean recursion depth of bb_dominates() is 860,
> which means that there are chains of bb->parent as long as 860.

Yes, that is the impression I get as well for, some where the finding
dominates is taking a lot of time. Also the result is not saved.

>
> By restricting the bb_dominates() in CSE to a reasonable depth of 32,
> the compile time is reduced to .8s without changing a single bit in the
> resulting code.

We can revisit this after the release. I have side project work on finding
the dominatior tree.

Chris