[cmake-developers] Proposal to teach cmDepends to only take dependencies from the source tree

[Attila Krasznahorkay]

Hi Ben,

Maybe I shouldn't advertise these pages here, but in the end they are not secret either.

I only have hard numbers for the difference between specifying most of our includes with -isystem vs. specifying everything with -I. While still using SYSTEM includes, our full build took ~6 hours.

http://atlas-nightlies-browser.cern.ch/~platinum/nightlies/info?tp=g&nightly=CMAKE&rel=rel_0&ar=x86_64-slc6-gcc49-opt

Yesterday, after I updated the code to not use SYSTEM include paths anywhere, it went down to ~3 hours.

http://atlas-nightlies-browser.cern.ch/~platinum/nightlies/info?tp=g&nightly=CMAKE&rel=rel_2&ar=x86_64-slc6-gcc49-opt

I expect that the change in cmDepends will win us some more time over this. (I'm hoping for another 10% maybe.) But I don't have any firm numbers on that yet, as I didn't put my patched CMake version into our nightly build system yet. I just saw in some test jobs that rebuilding a small part of our software was a lot faster with this change.

Cheers,
            Attila

> On 09 Dec 2015, at 15:38, Ben Boeckel <ben.boeckel at kitware.com> wrote:
> 
> On Wed, Dec 09, 2015 at 09:19:45 +0100, Attila Krasznahorkay wrote:
>> I myself am on the side of simplicity. Using regular expressions would
>> allow us to do what I want. But if >95% of the people using this new
>> possibility would use it exactly like I plan to, then implementing it
>> in a more complicated way than necessary would just be a bad design
>> choice.
> 
> Do you have performance numbers for the change in your build between
> using include_directories (or target_include_directories), with and
> without SYSTEM, each with and without this change?
> 
> --Ben