Fix swift error throwing on non-darwin ARM platforms

[johnno1962]

A minor change to get Swift Error throwing to work on non-darwin ARM32 platforms (e.g. Android.) Without this change, code generated saves and restores ARM register r8 at the entry and returns of a function that throws. As r8 is used as a virtual return value for the object being thrown this gets overwritten by the restore and calling code is unable to catch the error. This was causing do/try/catch not to work on Android as it is an ARM32 platform that does not satisfy "STI.isTargetDarwin()"

Addresses SR-5438

[johnno1962]

There was an issue but it’s been resolved by completely clearing out the build directory and restarting. This looks good to go.

[rjmccall]

Yes, this looks right to me.

[rjmccall]

Ideally Manman Ren would review this, but she's no longer working on this project.

[rjmccall]

This patch should go into the main LLVM repository, though.

[rjmccall]

@aschwaighofer Please review and help this land in LLVM.

[johnno1962]

Thanks @rjmccall, @aschwaighofer, I think I have found someone to propose this patch to llvm - @modocache

[johnno1962]

Awaiting review on llvm: https://reviews.llvm.org/D35835

[aschwaighofer]

@modocache @johnno1962 The change looks good but needs a test case. I have left a review at the llvm's review site.

Thank you!

[johnno1962]

@aschwaighofer , @rjmccall. I understand this patch has landed in llvm trunk if you want to cherry-pick it up. Thanks @modocache.

[johnno1962]

Seems like you’ve picked this up. I’ll close the PR now - Thanks!