Bug#763078: confirmed llvm change broke ghc

[Joey Hess]

Gianfranco Costamagna wrote:
> llvm maintainer (Sylvestre) says that llvm-3.4 is going to disappear
> (not before jessie, but somewhen after), and llvm-3.5 is built
> correctly on arm{el,hf}.
> 
> Isn't it better to just upload with llvm-3.5 and do some binNMUs
> instead of using the old one and be hit (or be a blocker) for the
> future RM llvm-3.4 bug?
> 
> I'm just wondering if there is something behind the 3.4 decision.

Debian-release wrote:
> *Remember*: On the 5th of November, the version of your package *in
> testing* must be in its desired state for Jessie.

I think we will need to do that, at an appropriate point in the release
cycle. I'd say just after the release is out, rather than now.

* Rebuilding packages on armel and armhf could take quite some time.
* Assuming the objects built with 3.4 are not compatable with those
  built with 3.5, packages might need to be rebuilt in dependency order,
  which I don't know if we have automated.
* The newly built stuff would have no testing compared with the stuff
  in the archive.
* I don't know if simply rebuilding ghc with the new llvm works.
  (I don't even know what the root cause of the failure is.)
  I know that ghc contains llvm code generation and that it has had to
  be patched in the past for compatability with different versions of
  llvm.
* There would probably be some bootstrapping step in building ghc with
  this change. I haven't thought out how it would work.
* We will want to be upgrading to a new ghc after jessie anyway, and
  it seems likely at that point any llvm-3.5 compatability issues would
  be sorted out upstream already for us.
* In any case, my modifications to ghc to make it explicitly use a
  single version of llvm are the right thing to do, and a necessary first
  step.

-- 
see shy jo
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