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

[Chris Bieneman]

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 <mailto: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 <mailto:gribozavr at gmail.com>>*/

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