[cfe-dev] Building Clang on Windows

[Bruce Hoult via cfe-dev]

On Tue, Oct 16, 2018 at 11:42 PM, Kim Gräsman via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

>
> On Wed, Oct 17, 2018, 03:56 Fábio Picchi via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>
>>
>> What if cmake generated by default a solution that builds using only a
>> single thread? This way people would not complain when trying to use this
>> workflow and mantainers / more experienced users would change this setting
>> when they find it appropriate.
>>
>
> MSVC has two knobs for parallel compilation: the compiler switch /MP which
> can be set per project or per source file, and "Number of parallel builds"
> which is a user setting and can't be overridden for individual
> solutions/projects.
>
> So I suppose the cmake system could generate projects without /MP, but the
> other setting is out of its control.
>
> And I'm not sure it makes a good default to cripple the buildsystem like
> this. For every user it helps, it will kill the experience for somebody
> else.
>

Exactly.

I tried it on the dev machine I use.

brucehoult at gamma05:~/riscv/riscv-llvm/_build$ time cmake --build . -- -j1
[2672/2672] Creating library symlink lib/libbenchmark_main.so.0
lib/libbenchmark_main.so

real 136m51.168s
user 125m28.820s
sys 10m30.132s

The normal time for a clean build on this machine is 8.5 minutes. Even on
my little i7 NUC it's only about 30 minutes. Who would want to wait over
two hours?
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