[Mesa-dev] [PATCH 1/2] i965: retype result of typed atomic operation to the same type as source

[Francisco Jerez]

Ilia Mirkin <imirkin at alum.mit.edu> writes:

> On Mon, Feb 22, 2016 at 5:21 PM, Francisco Jerez <currojerez at riseup.net> wrote:
>> Ilia Mirkin <imirkin at alum.mit.edu> writes:
>>
>>> On Mon, Feb 22, 2016 at 3:53 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>>>> On Mon, Feb 22, 2016 at 3:52 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>>>>> This fixes atomic exchange with a r32f image, as needed by
>>>>> GL_OES_shader_atomic_exchange.
>>>>
>>>> Sorry, that should be GL_OES_shader_image_atomic of course.
>>>>
>>>>>
>>>>> Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
>>>>> ---
>>>>>  src/mesa/drivers/dri/i965/brw_fs_surface_builder.cpp | 6 ++++--
>>>>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/src/mesa/drivers/dri/i965/brw_fs_surface_builder.cpp b/src/mesa/drivers/dri/i965/brw_fs_surface_builder.cpp
>>>>> index 081dbad..e775cc0 100644
>>>>> --- a/src/mesa/drivers/dri/i965/brw_fs_surface_builder.cpp
>>>>> +++ b/src/mesa/drivers/dri/i965/brw_fs_surface_builder.cpp
>>>>> @@ -156,8 +156,10 @@ namespace brw {
>>>>>           const fs_reg tmp = bld.vgrf(BRW_REGISTER_TYPE_UD, n);
>>>>>           bld.LOAD_PAYLOAD(tmp, srcs, n, 0);
>>>>>
>>>>> -         return emit_send(bld, SHADER_OPCODE_TYPED_ATOMIC_LOGICAL,
>>>>> -                          addr, tmp, surface, dims, op, rsize);
>>>>> +         return retype(
>>>>> +            emit_send(bld, SHADER_OPCODE_TYPED_ATOMIC_LOGICAL,
>>>>> +                      addr, tmp, surface, dims, op, rsize),
>>>>> +            src0.type);
>>>
>>> Actually I've been thinking a bit more about this... relying on
>>> src0.type won't fly. The surface's mesa_format needs to be passed
>>> through to emit_image_atomic, just like it is done for emit_image_load
>>> and emit_image_store. And I need to fix up the vec4 emitter. Curro,
>>> does that sound reasonable? Or should the retype be done at the
>>> emit_image_atomic callsites?
>>>
>> I doubt it's necessary to pass the surface format through.
>
> Well, you have to get the format from somewhere. You could easily have e.g.
>
> int foo, bar;
>
> foo = floatBitsAsInt(imageAtomicExchange(img, intBitsAsFloat(bar)));
>
> I believe in this scenario, src0.type is likely to be "int" instead of
> "float". Both of our fixes suffer from this problem.

No, the src type is only dependent on the image type.  If the image is
float you'll get a float.

>
>> Any reason
>> we shouldn't go with this series I sent half a year ago instead? (and you
>> actually commented to)
>>
>> https://lists.freedesktop.org/archives/mesa-dev/2015-August/091948.html
>> https://lists.freedesktop.org/archives/mesa-dev/2015-August/091949.html
>> https://lists.freedesktop.org/archives/mesa-dev/2015-August/091950.html
>> https://lists.freedesktop.org/archives/mesa-dev/2015-August/091951.html
>> https://lists.freedesktop.org/archives/mesa-dev/2015-August/091952.html
>
> Mainly that I forgot all about it :) Not sure if I commented on it
> back then, but I don't think we need a separate enable bit. Definitely
> not for TGSI (which is a lot more typeless), and it seems like not for
> i965 either. Also note that this behaviour is core in GLES 3.2 (and GL
> 4.5).
>
IIRC the series I sent already enabled the built-ins for GLES3.2 and
GL4.5 even though GLES3.2 had just been released.  I don't think any
additional work is required.

>   -ilia
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