Re: Link-Time Optimisation

2012-03-03 Thread Thorsten Glaser
Aron Xu dixit:

You might be interested in reading this thread:
http://lists.debian.org/debian-devel/2011/06/msg00149.html

Ok, will have a look, thanks.

Activating LTO by default seems not to be a reasonable idea (reasons

Right, it is not.

are in the given thread), but if maintainer of a package see it's
appropriate then he can use it in the package.

Yes, that was my intention, I just wondered whether people
were using it in their packages at all, and provided an
example for others to use or even improve.

bye,
//mirabilos
-- 
  “Having a smoking section in a restaurant is like having
  a peeing section in a swimming pool.”
-- Edward Burr


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Link-Time Optimisation

2012-03-02 Thread Thorsten Glaser
Hi all,

has anyone ever wondered about adoption of LTO in Debian?

I’ve been using -fwhole-program --combine since GCC supported
it somewhat reliably (with a fallback as they have broken it
regularily at least three times) in mksh, and now several of
my packages try -flto=jobserver with a fallback. (This does
not break clang, but it doesn’t take profit of clang’s possible
whole-programme optimisations either. But since clang was not
yet a viable compiler for Debian official packages, I have not
invested into it yet – mksh upstream can utilise it.)

But who else is doing that?

Good examples for how to do this are src:kwalletcli and src:pax
since recently. They also use dpkg-buildflags only if available.
(Of course, if someone knows of improvements once seeing their
rules files, which do NOT involve cdbs or dh7, do tell.)

Due to the fallbacks, backports to Debian releases with gcc 4.4
or older work, and failures to LTO or combine do not abort the
compilation.

One drawback is #650145 which even occurs with -Wl,--as-needed,
but that’s really cosmetic in virtually all cases. Somewhat
longer build times and memory consumption too (which gcc-4.6
LTO reduces again though), but hey, even m68k can do it…

Please Cc me on replies. Thanks.

bye,
//mirabilos
-- 
Solange man keine schmutzigen Tricks macht, und ich meine *wirklich*
schmutzige Tricks, wie bei einer doppelt verketteten Liste beide
Pointer XORen und in nur einem Word speichern, funktioniert Boehm ganz
hervorragend.   -- Andreas Bogk über boehm-gc in d.a.s.r


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Re: Link-Time Optimisation

2012-03-02 Thread Aron Xu
Hi Thorsten,

You might be interested in reading this thread:
http://lists.debian.org/debian-devel/2011/06/msg00149.html

Activating LTO by default seems not to be a reasonable idea (reasons
are in the given thread), but if maintainer of a package see it's
appropriate then he can use it in the package.



-- 
Regards,
Aron Xu


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