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Re: alias time explosion
On 3/21/06, Andrew MacLeod <amacleod@redhat.com> wrote:
> On Mon, 2006-03-20 at 18:55 -0500, Andrew Pinski wrote:
> > On Mar 20, 2006, at 5:18 PM, Andrew MacLeod wrote:
> >
> > > I'm not sure when this happened, but I noticed on the weekend that
> > > there
> > > has been an explosion in the time spent during the alias analysis
> > > phase.
> > > using cplusplus-grammer.ii, it use to compile on my machine in about 55
> > > seconds, and its now up to about 150 seconds.
> > >
> > > A quick gprof indicated about 60% of compile time is being spent in
> > > bitmap_bit_p, called from compute_may_aliases.
> > >
> > > someone made it WAY slow :-)
> >
> > Could it be that 2 more passes of may_alias was added?
>
> I don't think so. I would expect that to double or triple the time spent
> in alias analysis, not the entire compile time. This is a 200% increase
> in compiler time... going from 50 seconds to 150 is pretty significant.
> And since its almost all in bitmap_bit_p, it sounds algorithmic to me...
>
> btw, this was on a 3.0 Ghz P4 running linux with a checkout from
> mainline this morning built with no checking...
>
> Doing a quick check back, on 01/23 shows similar time (71% of compiler
> time spent in alias analysis, 97 seconds out of 135). The previous
> compiler to that which I have laying around is 10/30/05, and it shows a
> much more sensible 6.32 seconds in alias analysis.
>
> It looks like sometime between 10/30 and 01/23 alias analysis got out of
> hand. Odd it hasn't been noted before.
Can you do a comparison to 4.1.0 and file a PR with the testcase please?
Thanks,
Richard.