Due to the speed at which LLVM/Clang and Swift move, we do not build Swift against ToT LLVM. We tried this in the past and it resulted in us spending a lot of time dealing with upstream churn and not working on swift. To work around this problem, we now build against stable snapshots of LLVM/Clang that are updated as soon as possible given a minimum break of 2-3 weeks in between such updates (1).
Later this week, I will be performing such an update to the stable snapshots of LLVM/Clang. This will involve changes to Swift and LLDB to work with the new LLVM/Clang. I will send out an email the day I perform it as well as right before I perform the operation.
I have verified that these changes work on the current x86_64 OS X/ubuntu builds via the CI system. For those supporting other platforms if one wishes to test against the stable merge before it lands please check out the following branches:
2. swift-clang: stable-next
Then perform the normal work flow for testing your build.
(1) The reason for mentioning a minimum and not a maximum time is that sometimes it takes longer to perform a merge due to disruptive upstream changes. The minimum cadence is meant to provide some stability even if the upstream changes are not disruptive.