[llvm-dev] GN build roundtable summary; adding GN build files to the repo

[Dean Michael Berris via llvm-dev]

FWIW, this is consistent with my experience as well.

I also wrote a presubmit script that I run locally to build/test the cross-product of:

COMPILER={gcc+gold, clang+lld}
MODE={debug, release-with-assertions}
TARGETS={llvm+clang+lld+compiler-rt, compiler-rt(standalone)}

While the build/test times are helped by using ninja, the CMake config times are less than optimal.

It’s bad enough that I think I’ll give gn a whirl if the files were in the project(s) too.

> On 1 Nov 2018, at 09:33, Zachary Turner via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> And by the way, that is with my cache already populated.  Here it is on a fresh build directory where it has to generate everything.  (this time release build)
> 
> $ timecmd cmake -G Ninja -DLLVM_ENABLE_PROJECTS=clang;lld;lldb -DLLVM_TARGETS_TO_BUILD=X86 -DCMAKE_BUILD_TYPE=Release ..\..\..\..\llvm-mono\llvm
> <output snipped>
> command took 0:0:57.42 (57.42s total)
> 
> This is on a 48-core machine btw, with an SSD.
> 
> On Wed, Oct 31, 2018 at 3:29 PM Zachary Turner <zturner at google.com> wrote:
> On Wed, Oct 31, 2018 at 3:11 PM Nicolai Hähnle via llvm-dev <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)
> 
> 
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

-- Dean