[Mesa-dev] [PATCH 3/3] st/mesa: use PK2H/UP2H when gs5 is supported

[Marek Olšák]

On Thu, Oct 29, 2015 at 8:07 AM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> On Thu, Oct 29, 2015 at 2:52 AM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>> ARB_gpu_shader5 should be a decent proxy for whether those instructions
>> are supported.
>>
>> Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
>> ---
>>
>> Not actually ready to be committed, since r600/radeonsi need support
>> for these ops as well. Should be easy to implement, but want to get
>> the OK before I do so.
>
> Oh, and to pre-empt the question of "why not the other pack/unpack
> primitives", it's because nouveau codegen is able to optimize them
> into reasonable forms (it does better with unpack than with pack), esp
> after I adjusted the lowering passes to use BFI/BFE. Not ideal, but
> the manual f32 <-> f16 stuff was a bit much. I wouldn't be opposed to
> the other opcodes getting added too, just didn't seem too important.

Yeah, the integer packing opcodes are a lot easier to recognize in
driver backends.

Patches 1 & 3 are:
Reviewed-by: Marek Olšák <marek.olsak at amd.com>

Of course, r600 and radeonsi support needs to be done before pushing this patch.

radeonsi has 2 ways of converting float->half:

Using these LLVM intrinsics, which are translated to instructions that
obey round mode rules:
llvm.convert.to.fp16
llvm.convert.from.fp16

Using this SI LLVM intrinsic, which rounds towards zero and is used
for converting fragment color outputs:
llvm.SI.packf16

I think we should use the former for consistency, even though the GLSL
4.4 spec states that the rounding mode is undefined.

Marek