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Re: [ast-optimizer-branch] Simplification is pretty expensive
On Tue, 2002-06-04 at 13:35, Jan Hubicka wrote:
> > On Tue, 2002-06-04 at 13:22, Jan Hubicka wrote:
> >
> > > I tought it just enabled the simplification pass?
> > >
> > Yes, but simplification was not really enabled until we fixed the
> > bootstrap problems.
> Even more interesting...
> Why was the builds failing with -ftree-ssa then?
>
Because simplification had bugs, obviously. But I was a bit misleading
in my previous post.
Prior to last week, much of the simplifier was ifdef'd out in the
branch. So, -ftree-ssa would have some effect, but it would only
re-write some types of trees.
Since it wasn't re-writing everything, the performance degradation
wasn't very noticeable. Once we fixed all the bugs and fully enabled
simplification the degradation became very noticeable.
In any case, I wouldn't be surprised if tree simplification has some
negative effect on SPEC scores (remember that none of the tree
optimizers are enabled now). The hope is of course to start climbing up
the performance ladder with the new tree optimizers. But we must pay
attention to the compile time degradation. It's pretty significant.