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Re: alias time explosion


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.

Andrew


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