[Mesa-dev] TGSI declarations missing type info

[Christoph Bumiller]

On 13.11.2011 17:32, Christoph Bumiller wrote:
> On 13.11.2011 17:10, Marek Olšák wrote:
>> I am guessing there is no type info because TGSI shaders are allowed
>> to use uint, sint, and float instructions on the same register without
>> type conversions (it would be possible to generate such usage with
>> GL_ARB_shader_bit_enconding, also GL_NV_gpu_program4 has typeless
>> registers too). I think GLSL has types because it's a typed language,
>> not because it's needed for the underlying implementation. Do all
>> drivers need such info or is it just llvmpipe that would make use of
>> it?
> If you don't have typed values in your backend IR and the hardware
> doesn't have dedicated integer and float registers, you don't need type
> info.
>
> With llvm you have both typed values and, for x86, different registers
> for integers and floats, so it seems it would be very helpful not to
> destroy all that information (gallium's favourite thing to do) before
> passing shaders to the driver.

Actually never mind, I just realized TEMPs are all stored in memory in
llvmpipe, so you can just load into a value of the appropriate type, as
determined by the instruction.

For example, in lp_bld_tgsi_soa.c, emit_fetch, FILE_TEMPORARY case you have:

" cast temps_array pointer to float* " -- just do the same with int or
whatever type your require and you should be fine.

> For nv50 and nvc0 I don't need to know the type ... for ints and floats.
>
> *But* for doubles (any kind of value that occupies multiple TGSI
> register components) the driver's internal IR will give me the same
> headache that you will have for llvmpipe when you can't be sure whether
> you need 1 or 2 IR values for TEMP[i].xy.
>
> So, an issue with types will come up for other drivers, too, eventually.
>
> The SM4 IR does the same as TGSI though and also doesn't provide type
> information, so the problem should be solveable, but the solution might
> not be pretty.
>
>> It's like you said: Right now TGSI temporaries are like unions in C.
>> Only the instructions are typed (MAX vs IMAX vs UMAX).
>>
>> Marek
>>
>> On Sun, Nov 13, 2011 at 4:06 PM, Dave Airlie <airlied at gmail.com> wrote:
>>> Hi guys,
>>>
>>> Just been looking at llvmpipe integer support and it seems like we
>>> lose some information about the type of data stored into temporaries,
>>>
>>> after st_glsl_to_cpp we no longer know what type the temporaries are,
>>> and llvm would really like to know and I can't see any reason that
>>> TGSI doesn't contain the info. Having untyped temp decls means we'd
>>> have to allocate some sort of "union" via aliases I guess in llvmpipe
>>> for all temps so we can store int/float in them.
>>>
>>> I've attached a run of glsl-vs-loop from llvmpipe with integer opcodes
>>> forced on. (llvmpipe-int-test branch of my repo).
>>>
>>> Dave.
>>>
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>>>
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