[lowrisc-dev] Re: [sw-dev] RISC-V LLVM status update

David Chisnall David.Chisnall at cl.cam.ac.uk
Tue Sep 19 11:54:06 BST 2017


On 19 Sep 2017, at 11:43, Alex Bradbury <asb at asbradbury.org> wrote:
> 
> I was actually going to make a slight change in approach for the
> llvm-integration repo, motivated by the desire from you (Andes) to
> work on top of an LLVM 5.0 base. There are advantages and
> disadvantages to this

Having tried both approaches, I’d say that the disadvantages massively outweigh the advantages.  There’s usually a lot of churn in the back-end APIs in LLVM (and as GlobalISel becomes the default, this is not going to slow down any time soon).  Trying to upgrade an entire release at once is a lot of effort and a lot more effort than doing regular merges from upstream.  Worse, you don’t catch regressions in other parts of the system that only affect your back end until a release is out, at which point it’s hard to find the exact commit that broke things for you and it’s no longer fresh in the mind of the person that wrote it.

David




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