[Mesa-dev] [RFC PATCH 00/16] A new IR for Mesa

[Henri Verbeet]

On 21 August 2014 04:56, Michel Dänzer <michel at daenzer.net> wrote:
> On 21.08.2014 04:29, Henri Verbeet wrote:
>> For whatever it's worth, I have been avoiding radeonsi in part because
>> of the LLVM dependency. Some of the other issues already mentioned
>> aside, I also think it makes it just painful to do bisects over
>> moderate/longer periods of time.
>
> More painful, sure, but not too bad IME. In particular, if you know the
> regression is in Mesa, you can always use a stable release of LLVM for
> the bisect. You only need to change the --with-llvm-prefix= parameter to
> Mesa's configure for that. Of course, it could still be mildly painful
> if you need to go so far back that the current stable LLVM release
> wasn't supported yet. But how often does that happen? Very rarely for me.
>
Sure, it's not impossible, but is that really the kind of process you
want users to go through when bisecting a regression? Perhaps throw in
building 32-bit versions of both Mesa and LLVM on 64-bit as well if
they want to run 32-bit applications.

> Without LLVM, I'm not sure there would be a driver you could avoid. :)
>
R600g didn't really exist either, and that one seems to have worked
out fine. I think in a large part because of work done by Jerome and
Dave in the early days, but regardless. From what I've seen from SI, I
don't think radeonsi needed to be a separate driver to start with, and
while its ISA is certainly different from R600-Cayman, it doesn't
particularly strike me as much harder to work with.

Back to the more immediate topic though, I think think that on
occasion the discussion is framed as "Is there any reason using LLVM
IR wouldn't work?", while it would perhaps be more appropriate to
think of as "Would using LLVM IR provide enough advantages to justify
adding a LLVM dependency to core Mesa?".