[Mesa-dev] [PATCH] Add (un)packHalf tests which don't fail on GCN

[Marek Olšák]

On Fri, Feb 5, 2016 at 10:57 AM, Marek Olšák <maraeo at gmail.com> wrote:
> On Fri, Feb 5, 2016 at 1:55 AM, Matt Turner <mattst88 at gmail.com> wrote:
>> On Thu, Feb 4, 2016 at 10:50 AM, Marek Olšák <maraeo at gmail.com> wrote:
>>> From: Marek Olšák <marek.olsak at amd.com>
>>>
>>> This is a subset of the generated tests which are known to fail
>>> on everything except CPU emulation (AFAIK).
>>> ---
>>
>> This is really awful. Committing a generated test, but with unknown
>> bits chopped out is gross.
>>
>> If it were me, I'd want to understand why my hardware behaved
>> differently -- not just hack up *different* tests and claim victory.
>>
>> FWIW, the generated tests pass on all Intel hardware exposing
>> ARB_shading_language_packing. Gen7+ has native half-float support, and
>> Gen6 uses the lowering code in lower_packing_builtins.cpp to turn the
>> built-ins into a pile of instructions.
>>
>> If you can identify how AMD hardware behaves differently and can prove
>> that the generator needs to be relaxed or something, that's cool. But
>> as is, I hate this patch.
>>
>> I can't find anything in the AMD docs (I looked at GCN3) about
>> half-precision support, so I can't check my theory that AMD hardware
>> rounds towards zero instead of to-nearest/even like Intel.
>
> Since the tests only fail with very small numbers, I think the problem
> is that denorms are disabled by radeonsi. I can try to confirm that.
>
> The hardware rounds to nearest even. The hw precision is:
> - unpack functions - 0 ULP
> - pack functions = 0.5 ULP
> - input and output denorms are flushed to 0

Hey Matt,

I have just confirmed that I was right. After I enable denormals in
hw, the original tests pass. This means that this patch tests the
packing functions but skips denormals.

Not so awful now, is it? :)

Sadly, I can't enable denormals on all chips, because they are slow.

So if I add "-no-denormals" suffix into the test names, I can push this, right?

Marek