Re: is LTO aimed for large programs?

[Robert Dewar <dewar at adacore dot com>]

Jan Hubicka wrote:
> > > Perhaps the question is when not to use -flto and use -fwhopr instead?
> > My rule of thumb is: Try -flto first, if it does not work (running out
> > of memory), try -fwhopr. I think the advantage of -flto is also that it
> > is better tested, while -fwhopr has known issues.
>
> -fwhopr is quite broken in the current implementation and I am not sure
> we can resoably fix it in stage3, so -flto is only choice for the moment
> for larger programs. If it explodes in memory use, I would be interested
> in having the testcase.

Always hard to know what explode means. We have customers with programs
large enough that normal -O2 optimization blows 32-bit address limits,
and they have had to move to 64-bit machines to complete compilation.
> Honza
> > Tobias
> >
> > [1] http://gcc.gnu.org/ml/gcc/2009-10/msg00122.html
> > [2] http://moene.org/~toon/GCCSummit-2006.pdf