[swift-dev] compiler-rt...Wait wat?

[Bob Wilson]

> On Aug 17, 2016, at 5:48 AM, Ryan Lovelett via swift-dev <swift-dev at swift.org> wrote:
> 
> I just noticed that if you do `utils/update-checkout --clone` it pulls
> down `compiler-rt`. I have been building Swift from source on Linux for
> awhile now. I've never once checked out compiler-rt. Which makes me
> wonder if that repository is even in use.
> 
> Here is the question: what is the compiler-rt repository used for? Is my
> build not working as expected without compiler-rt?

At least one reason is that the runtime support for code coverage testing is in compiler-rt. We want to be able to test Swift’s support for code coverage and we need the runtime library to be able to run those tests.