[swift-dev] Cross-compile for Android armv7 from OSX

[Dmitri Gribenko]

All phases are compiling different libraries.  The serial part is the
first stage when we compile the core library, that every other library
depends on, and another serial stage is StdlibUnittest, that depends
on many other libraries, but just takes too long to compile, and its
compilation outlives the parallel stage when we still have other work
to do.

Dmitri

On Fri, Jan 22, 2016 at 10:10 AM, Chris Bieneman <beanz at apple.com> wrote:
> What are the very parallel and very serial phases doing?
>
> -Chris
>
> On Jan 22, 2016, at 10:03 AM, Dmitri Gribenko <gribozavr at gmail.com> wrote:
>
> On Fri, Jan 22, 2016 at 9:50 AM, Chris Bieneman <beanz at apple.com> wrote:
>
>
> On Jan 22, 2016, at 9:30 AM, Dmitri Gribenko <gribozavr at gmail.com> wrote:
>
> On Fri, Jan 22, 2016 at 9:26 AM, ChrisBieneman <beanz at apple.com> wrote:
>
> Can I provide an alternate suggestion?
>
> Clang can be cross-compiled for alternate platforms with seemingly a single
> CMake invocation. This is accomplished by having a model where the user
> configures the cross-build, and LLVM's CMake detects that you are cross
> compiling and it handles configuring the host tools and hooking the
> dependencies up.
>
> This does lead to some pretty gnarly CMake scripting, but I think it
> provides a very good user experience.
>
> As an example instructions for cross-compiling LLVM are here:
> http://llvm.org/docs/GettingStarted.html#cross-compiling-llvm
>
> That simple configuration command handles everything, all a user has to do
> is run ninja once.
>
>
> Does that ninja command invoke multiple sub-ninja commands?
>
>
> Yes. The top-level ninja will put them in the console job pool which results
> in their output being directly piped to the parent, and only one will
> execute at a time which allows them to not conflict with each other.
>
>
> Well, that's bad, here's why.
>
> Building the Swift standard library has two phases: a very parallel
> one, and a strictly serial one.  If you run all ninja invocations
> serially, you will be increasing the compilation time by about 8x for
> a full build for Apple operating systems (approx. 1 hour in total,
> unacceptable).  If you run them all in parallel, you will
> oversubscribe the machine during the parallel phase, and it will start
> swapping.
>
> Dmitri
>
> --
> main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
> (j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr at gmail.com>*/
>
>



-- 
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr at gmail.com>*/