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

[Michel Dänzer]

On 21.08.2014 18:10, Henri Verbeet wrote:
> 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?

I appreciate your theoretical concern, but in practice, people don't 
seem to have trouble bisecting radeonsi regressions in general.


>> 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.

That's getting off-topic, but most of the code that can be shared 
between radeonsi and r600g is shared now.


> 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?".

Unless you can show me anyone who would prefer swrast or softpipe over 
llvmpipe for software rendering tests, I'd argue that there effectively 
already is such a dependency. There's no real indication that using LLVM 
IR for the purposes discussed in this thread would require a stricter 
dependency on LLVM than we already have for llvmpipe.


-- 
Earthling Michel Dänzer            |                  http://www.amd.com
Libre software enthusiast          |                Mesa and X developer