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

[Michel Dänzer]

On 21.08.2014 03:13, Kenneth Graunke wrote:
> On Wednesday, August 20, 2014 06:41:08 PM Michel Dänzer wrote:
>> On 20.08.2014 00:04, Connor Abbott wrote:
>>> 
>>> we've already had problems where distros refused to ship newer
>>> Mesa releases because radeon depended on a version of LLVM newer
>>> than the one they were shipping, [...]
>> 
>> That's news to me, can you be more specific?
>> 
>> That sounds like basically a distro issue though, since different
>> LLVM versions can be installed in parallel (and the one used by
>> default doesn't have to be the newest one). And it even works if
>> another part of the same process uses a different version of LLVM.
> 
> Yes, one can argue that it's a distribution issue - but it's an
> extremely painful problem for distributions.
> 
> For example, Debian was stuck on Mesa 9.2.2 for 4 months (2013-12-08
> to 2014-03-22),

Speaking as a former Debian Developer (and still watching the X driver
stack related Debian mailing lists and IRC channel), that is usually due
to lack of volunteer time more than anything else.

> and I was told this was because of LLVM versioning changes in the other
> drivers (primarily radeon, I believe, but probably also llvmpipe).
> 
> Mesa 9.2.2 hung the GPU every 5-10 minutes on Sandybridge, and we
> fixed that in Mesa 9.2.3.  But we couldn't get people to actually
> ship it, and had to field tons of bug reports from upset users for
> several months.

I don't see any changes between 9.2.2 and 9.2.3 which would require a
newer version of LLVM.

Anyway, if anything like that ever comes up again, please talk to the
radeonsi developers about it. We're right here, you know. :) We can
certainly consider supporting older versions of LLVM if there is demand
for that.


> I've also heard stories from friends of mine who use radeonsi that
> they couldn't get new GL features or compiler fixes unless they
> upgrade both Mesa /and/ LLVM, and that LLVM was usually either not
> released or not available in their distribution for a few months.

Again, this has been a problem sometimes but not as much with LLVM point
releases.


> Those are the sorts of things I'd like to avoid.

That's fine, using LLVM IR doesn't require you to use an LLVM compiler
backend, let alone to maintain it in the LLVM tree (remember that we
were maintaining the LLVM R600 backend in Mesa initially, but the
trade-off is better for us in the LLVM tree).


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

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