Re: upcoming API changes for LLVM 12

Hi Andres,

On Thu, Oct 15, 2020 at 6:12 PM Andres Freund <andres@anarazel.de> wrote:
>
> Hi,
>
> There will be a breaking API change for JIT related API in LLVM
> 12. Mostly about making control over various aspects easier, and then
> building on top of that providing new features (like JIT compiling in
> the background and making it easier to share JIT compiled output between
> processes).
>
> I've worked with Lang Hames to ensure that the new C API has feature
> parity...
>

I assume you're alluding to the removal of ORC legacy (v1) API? How far
back was feature parity in the new API, or we could only switch starting
with LLVM 12?

> The postgres changes are fairly localized, all in llvmjit.c - it's just
> a few #ifdefs to support both LLVM 12 and before.
>
> The two questions I have are:
>
> 1) Which versions do we want to add LLVM 12 support?  It'd be fairly
>    easy to backport all the way. But it's not quite a bugfix... OTOH,
>    it'd probably painful for packagers to have dependencies on different
>    versions of LLVM for different versions of postgres.
>
> 2) When do we want to add LLVM 12 support? PG will soon stop compiling
>    against LLVM 12, which will be released in about 6 months. I worked
>    with Lang to make most of the breaking changes in a branch (to be
>    merged in the next few days), but it's possible that there will be a
>    few smaller changes.

I think this has already happened about two weeks ago when Lang's commit
6154c4115cd4b78d landed in LLVM master.

Cheers,
Jesse