llvm dev - Nov 2018 - GN build roundtable summary; adding GN build files to the repo

On 31.10.18 23:29, Zachary Turner wrote:
> 
> On Wed, Oct 31, 2018 at 3:11 PM Nicolai Hähnle via llvm-dev 
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>> wrote:
> 
> 
> 
>     Besides, how on earth are you using LLVM that cmake times are an issue?
>     Given that cmake times seem to be the only argument you have in
>     favor of
>     GN...
> 
>     I just measured the typical case (for LLVM only, debug build, all
>     non-experimental targets enabled) by touching all files. cmake takes 5
>     seconds to run, while the build as a whole takes about 5 minutes. (This
>     is on Ubuntu 18.10, in case that matters.)
> 
> 
> I am using CMake with LLVM with all targets OFF except for x86.  Only 
> clang, lldb, and lld enabled.
> 
> $ timecmd cmake ..\..\..\..\llvm-mono\llvm
> <output snipped>
> command took 0:0:34.05 (34.05s total)
Have you tried LLVM only?

Quite frankly, if I can get a cmake run in under 5 seconds for LLVM only 
(on a Threadripper with SSD) without doing anything special, and it 
takes your system 35 seconds for LLVM + Clang + LLDB + LLD (on an 
apparently similarly beefy system, also with SSD), it sounds to me like 
something *seriously* broken is happening in the cmake files for those 
other projects.

Maybe that should be fixed instead of reinventing the world?

Cheers,
Nicolai
> 
> 
-- 
Lerne, wie die Welt wirklich ist,
Aber vergiss niemals, wie sie sein sollte.

On 11/1/18 11:30 AM, Nicolai Hähnle via llvm-dev wrote:
> Have you tried LLVM only?
> 
> Quite frankly, if I can get a cmake run in under 5 seconds for LLVM only
(on a Threadripper with SSD) without doing anything special, and it takes your
system 35 seconds for LLVM + Clang + LLDB + LLD (on an apparently similarly
beefy system, also with SSD), it sounds to me like something *seriously* broken
is happening in the cmake files for those other projects.
> 
> Maybe that should be fixed instead of reinventing the world?
What would be the options to get a minimal build? I have checked out LLVM
from the git mirror and just ran cmake -G Ninja on an AMD EPYC with 32 cores,
it took 17 seconds. The whole build took 6 minutes and 20 seconds.

Either way, I'm very happy with cmake. It's powerful, proven and fast
enough
and it's very portable.

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer - glaubitz at debian.org
`. `'   Freie Universitaet Berlin - glaubitz at physik.fu-berlin.de
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