Re: [RFC] Contributing tree-ssa to mainline

[Roger Sayle <roger at eyesopen dot com>]

On Sat, 17 Jan 2004, Diego Novillo wrote:
> On Fri, 2004-01-16 at 23:19, Roger Sayle wrote:
> > For years I've (we've) been trying to break this glass ceiling.  Why is
> > is that impressive optimization passes do little to make up the short
> > fall.  Is it because they have partial dead-code elimination and we don't,
> > or that they can apply synthetic multiplication later, or that they have
> > better reassociation...  Intel's vectorization would be nice...
> >
> Those things are either planned or being worked on.  As I said before,
> we need to balance pros and cons.
>
> If we are to wait for all the possible optimizations (vectorization,
> memory hierarchy, loop transformations, etc) to be contributed, we may
> have to wait quite a bit longer than if we included the infrastructure
> in mainline.

Sorry, my comments weren't meant as a list of prerequsistes of passes
to be implemented in tree-ssa before it get considered for integration.
Rather to refute the argument that both mainline and tree-ssa are already
close to their potential performance limits.

I'm fully aware that there a numerous pending optimizations that can
be made using the new tree-ssa infrastructure.  It is this *potential*
for improvement that should be included in the PROs for the branch.
In the last two years, your and Andreas' SPEC testing have shown that
mainline has barely improved 10 points on SPECint.  Given that the
tree-ssa has jumped over 10 points in the last six months, and that
there's clearly more to come, then even if all other factors were equal,
it would make sense to vote for the more dynamic of the two.


[This e-mail may contain forward looking statements.  Performance
benchmarks and compile-times can go up as well as down.  Past
performance is no guarantee or indicator of future events.  :>]

Roger
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