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Re: [PATCH] Fix optimization regression in constant folder


On 9/29/07, Richard Guenther <richard.guenther@gmail.com> wrote:
> On 9/29/07, Eric Botcazou <ebotcazou@adacore.com> wrote:
> > > You still didn't come up with an optimization testcase which I asked for
> > > in the initial reply.
> >
> > Because it's time consuming.  The problem was identified on a 4.1-based
> > compiler (you applied the patch on the 4.1 branch too so it was picked for
> > our pre-production compiler and broke 2 big proprietary testcases there).
> >
> > Things have changed between 4.1 and 4.3 so the 2 testcases don't fail with the
> > latter like with the former and further work would be required.
>
> I'm happy with a testcase that only fails on 4.1 - that is, I don't see why
> either the code in fold is special, or why you don't need to adjust for
> example tree-ssa-reassoc.c on trunk with the same logic.  A testcase
> would give me something to look at myself, rather than trying to
> imagine what actually happens ;)

To make it clear - you seem to have a compelling case preserving
the special size types because we otherwise miss optimization opportunities.
I (and Roger in the past) try to get rid of them completely, so introducing
new dependence on this feature is exactly the opposite what I thought was
consensus.  Now, a testcase would maybe support your view.

[Getting rid of the special size types would also automatically get rid
of another source of confusion, namely that those special types are
sign-extended independent of their signedness]

Thanks,
Richard.


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