[Beignet] Building beignet with OpenCL 2.0 support in distros

[Rebecca N. Palmer]

I have a first attempt at "enable/disable 2.0 at run time" written, but 
haven't yet tested it.

On 21/01/17 16:08, Bruno Pagani wrote:
> Le 21/01/2017 à 16:55, Rebecca N. Palmer a écrit :
>
>> On 21/01/17 15:40, Bruno Pagani wrote:
>>> Le 21/01/2017 à 16:20, Rebecca N. Palmer a écrit :
>>>
>>>>> is there any downside in compiling with
>>>>> OpenCL 2.0 support,
>>>> Yes - on older (Ivybridge/Haswell - no emitUntypedReadA64Instruction)
>>>> hardware, a 2.0-enabled beignet won't work, at all.
>>>
>>> That’s what I’ve feared but after trying it here I haven’t encountered
>>> more issues than with a non-2.0-enabled beignet.
>>
>> Trying it on what hardware?  There might be hardware (all of gen8 if
>> this assert(0) is the only failure point) where a 2.0 build doesn't
>> crash outright but also doesn't have working 2.0.
>
> Haswell (HD4600).

Weird - are you sure darktable loads OpenCL by default?  For me 
(Ivybridge M GT2), everything that does immediately crashes with

clinfo: 
/home/rnpalmer/Debian/builds/stackbuild/beignet/backend/src/backend/gen_context.cpp:2259: 
virtual void gbe::GenContext::emitUntypedReadA64Instruction(const 
gbe::SelectionInstruction&): Assertion `0' failed.
Aborted

and that assert(0) only gets replaced by a real implementation in gen8 
and above, not in Haswell (gen75).