Re: libtool and LTO

[Ralf Wildenhues]

Hello Andi, Bob,

* Bob Friesenhahn wrote on Tue, Oct 05, 2010 at 12:30:51AM CEST:
> On Mon, 4 Oct 2010, Andi Kleen wrote:
> 
> >I discovered that libtool breaks gcc LTO (link time optimization)
> >
> >Is there a solution or a workaround known?
> >
> >I'm using libtool 2.2.6b
> 
> Maybe you should use libtool 2.4?

Yep, 2.4 should work with GCC LTO in every way *except* when partial
linking is involved in the process.  The latter should generally only
happen when command line length limits are exceeded.  We didn't try to
work around the 'ld -r' case because IIUC gold was going to be enhanced
to also support this OOTB (right?).

Getting Libtool 2.4 into GCC before 4.6 is on my list, by the way.

> [...] if you are using Automake I
> have heard that there are some fixes in development Automake which
> are needed/useful for -flto.

I'm not aware of fixes needed in Automake.  Care to point them out?

Thanks,
Ralf