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

[Connor Abbott]

On Wed, Aug 20, 2014 at 2:41 AM, Michel Dänzer <michel at daenzer.net> wrote:
> On 20.08.2014 00:04, Connor Abbott wrote:
>> On Mon, Aug 18, 2014 at 8:52 PM, Michel Dänzer <michel at daenzer.net> wrote:
>>> On 19.08.2014 01:28, Connor Abbott wrote:
>>>> On Mon, Aug 18, 2014 at 4:32 AM, Michel Dänzer <michel at daenzer.net> wrote:
>>>>> On 16.08.2014 09:12, Connor Abbott wrote:
>>>>>> I know what you might be thinking right now. "Wait, *another* IR? Don't
>>>>>> we already have like 5 of those, not counting all the driver-specific
>>>>>> ones? Isn't this stuff complicated enough already?" Well, there are some
>>>>>> pretty good reasons to start afresh (again...). In the years we've been
>>>>>> using GLSL IR, we've come to realize that, in fact, it's not what we
>>>>>> want *at all* to do optimizations on.
>>>>>
>>>>> Did you evaluate using LLVM IR instead of inventing yet another one?
>>>>
>>>> Yes. See
>>>>
>>>> http://lists.freedesktop.org/archives/mesa-dev/2014-February/053502.html
>>>>
>>>> and
>>>>
>>>> http://lists.freedesktop.org/archives/mesa-dev/2014-February/053522.html
>>>
>>> I know Ian can't deal with LLVM for some reason. I was wondering if
>>> *you* evaluated it, and if so, why you rejected it.
>
> First of all, thank you for sharing more specific information than
> 'table-flipping rage'.
>
>
>> * LLVM is on a different release schedule (6 months vs. 3 months), has
>> a different review process, etc., which means that to add support for
>> new functionality that involves shaders, we now have to submit patches
>> to two separate projects, and then 2 months later when we ship Mesa it
>> turns out that nobody can actually use the new feature because it
>> depends upon an unreleased version of LLVM that won't be released for
>> another 3 months and then packaged by distros even later...
>
> This has indeed been frustrating at times, but it's better now for
> backend changes since Tom has been making LLVM point releases.
>
> As for the GLSL frontend, I agree with Tom that it shouldn't require
> that much direct interaction with the LLVM project.
>
>
>> 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.

Sorry, I heard about this from one of the other Intel folks (I believe
Ian) so they'll have to comment more on it.

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