[Libreoffice] [GSoC] link-time optimization

[Jan Holesovsky]

Hi Honza,

So we have some proof-of-concept LTO work pushed to the LibreOffice
repository - care to have a look & try it how it copes with your changes
in gcc etc.? ;-)

git clone git://anongit.freedesktop.org/libreoffice/core
sudo zypper si -d libreoffice-bootstrap
./autogen.sh --enable-lto
make
make dev-install

More here: http://www.libreoffice.org/get-involved/developers/ , or
appear on #libreoffice-dev on irc.freenode.net :-)

All the best,
Kendy

On 2011-08-20 at 23:04 +0200, Matúš Kukan wrote:
> Hello,
> 
> I created patch, which allows link-time optimization (--enable-lto)
> for shared libraries, you need at least gcc-4.5 (I'm not checking for
> version in configure).
> gcc-4.5 is not really good for lto but I was able to install
> LibreOffice with lto enabled. I don't know what should I try to test
> if it is really faster and how much.
> Building is slower because gcc is compiling sources twice ? or
> something like that. But real problem is that lto is memory expensive.
> We could gain more with bigger libraries but it's not possible with
> gcc-4.5, I'm afraid.
> Unfortunately I was not able to install gcc-4.6, so I don't know if
> it's better but it should.
> 
> You can use gold as linker for elf libraries, it's really faster but
> linking phase it's not that much.
> Most of the time is running lto1 executable and it eat cca 2GB RAM
> when optimizing sw library. (cca 4,5 minutes for me)
> 
> So it is possible but not in parallel. And not for really big libraries.
> I am hoping it will be much better with gcc-4.6.
> 
> ok to push ? For sure there could be better message at least in configure.
> 
> Best regards,
> 
> Matúš
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