[Mesa-dev] [PATCH 4/9] gallium-tgsi: add TGSI_OPCODE_{FMA-POPCNT-MSB-LSB} description
Roland Scheidegger
sroland at vmware.com
Tue Jan 7 17:24:07 PST 2014
Yes, and I guess just about all GPUs can do that.
For llvmpipe we'd be vaguely interested in being able to do opencl-style
MAD with undefined rounding as FMA since (x86) cpus never have MAD but
may have FMA. I am not sure actually though this is ok for d3d10 -
interestingly d3d10 has only MAD for SP (saying it's just mul+add but
I'm unsure if that really means skipping the intermediate rounding is
prohibited), but only FMA for DP...
Roland
Am 07.01.2014 21:49, schrieb Marek Olšák:
> FYI, Evergreen has dedicated instructions for both MAD and FMA. FMA
> seems to be available on DX11 chips only.
>
> Marek
>
> On Tue, Jan 7, 2014 at 8:20 PM, Roland Scheidegger <sroland at vmware.com> wrote:
>> Yes that is certainly related. I'm actually not entirely sure what is
>> allowed in glsl by default as OpenGL seems to have some lax rules
>> regarding precision in any case (float calculations not required but
>> allowed to use denorms, at least earlier versions weren't required to
>> support Infs neither and so on).
>> It is quite possible the "MAD" we were always using would have been
>> allowed to really do fma (at least with OpenGL), unless the "precise"
>> qualifier was used (which isn't supported yet?).
>> TGSI also isn't really watertight about such issues neither (that is if
>> you use it with hw such as r300 then you certainly don't expect ieee754
>> rules to be followed but if you've got a d3d10-capable backend then you
>> are expected to follow rules specified there which are _mostly_
>> ieee754-2008).
>> So I'm not really sure if TGSI MAD should be allowed to do either
>> rounding or not, but someday it should be figured out and spelled out
>> explicitly in docs.
>>
>> Roland
>>
>>
>> Am 07.01.2014 19:24, schrieb Maxence Le Doré:
>>> I forgot the link :
>>>
>>> https://urldefense.proofpoint.com/v1/url?u=http://www.geeks3d.com/20120106/precise-qualifier-in-glsl-and-nvidia-geforce-cards/&k=oIvRg1%2BdGAgOoM1BIlLLqw%3D%3D%0A&r=F4msKE2WxRzA%2BwN%2B25muztFm5TSPwE8HKJfWfR2NgfY%3D%0A&m=%2FzSAl55KOH0z7T5qkRj6BX164wf6QpYOnJLIzojXBQc%3D%0A&s=0ac5e0fbd69867705f0c52090c9ddf84e7832be80e724a0983c5aa2f5dde72e0
>>>
>>> 2014/1/7 Maxence Le Doré <maxence.ledore at gmail.com>:
>>>> For this reason, GLSL 4.0 introduces the 'precise' qualifier. I invite
>>>> you to take a look at this article.
>>>>
>>>> 2014/1/6 Roland Scheidegger <sroland at vmware.com>:
>>>>> Am 05.01.2014 01:34, schrieb Maxence Le Doré:
>>>>>> FMA(a,b,c) keeps extra precision (usually 1 more bit of mantissa,
>>>>>> afaik) for the result a*b and add this to c, to finally produce a
>>>>>> IEEE754 32bit float result.
>>>>>>
>>>>>> MAD(a,b,c) product a IEEE754 32bit float product a*b and add it to C.
>>>>>>
>>>>>> So, fma can be slightly more accurate. An accuracy that is something
>>>>>> very appreciate.
>>>>>
>>>>> Actually in "newer" languages (such as opencl) "mad" is used to indicate
>>>>> intermediate rounding does not matter, so if your cpu can do fma but not
>>>>> mul+add in a single cycle it is allowed to use fma instead.
>>>>> FMA OTOH of course forces no intermediate rounding.
>>>>> Our tgsi definitions certainly initially were meaning intermediate
>>>>> rounding should take place, I don't know if we need to keep it that way
>>>>> or could repurpose that slightly (so if you require the intermediate
>>>>> rounding you'd just use mul+add).
>>>>>
>>>>> Roland
>>>>>
>>>>>
>>>>>
>>>>>>
>>>>>>
>>>>>> 2014/1/5 Marek Olšák <maraeo at gmail.com>:
>>>>>>> How is FMA different from MAD?
>>>>>>>
>>>>>>> Please document the new opcodes in src/gallium/docs/source/tgsi.rst.
>>>>>>>
>>>>>>> Marek
>>>>>>>
>>>>>>> On Sun, Jan 5, 2014 at 12:42 AM, Maxence Le Doré
>>>>>>> <maxence.ledore at gmail.com> wrote:
>>>>>>>> From: Maxence Le Doré <Maxence Le Doré>
>>>>>>>>
>>>>>>>> ---
>>>>>>>> src/gallium/auxiliary/tgsi/tgsi_info.c | 16 ++++++++++++++++
>>>>>>>> src/gallium/auxiliary/tgsi/tgsi_opcode_tmp.h | 6 ++++++
>>>>>>>> src/gallium/include/pipe/p_shader_tokens.h | 9 ++++++++-
>>>>>>>> 3 files changed, 30 insertions(+), 1 deletion(-)
>>>>>>>>
>>>>>>>> diff --git a/src/gallium/auxiliary/tgsi/tgsi_info.c b/src/gallium/auxiliary/tgsi/tgsi_info.c
>>>>>>>> index 0beef44..ed55940 100644
>>>>>>>> --- a/src/gallium/auxiliary/tgsi/tgsi_info.c
>>>>>>>> +++ b/src/gallium/auxiliary/tgsi/tgsi_info.c
>>>>>>>> @@ -221,6 +221,12 @@ static const struct tgsi_opcode_info opcode_info[TGSI_OPCODE_LAST] =
>>>>>>>> { 1, 3, 1, 0, 0, 0, OTHR, "TXL2", TGSI_OPCODE_TXL2 },
>>>>>>>> { 1, 2, 0, 0, 0, 0, COMP, "IMUL_HI", TGSI_OPCODE_IMUL_HI },
>>>>>>>> { 1, 2, 0, 0, 0, 0, COMP, "UMUL_HI", TGSI_OPCODE_UMUL_HI },
>>>>>>>> + { 1, 3, 0, 0, 0, 0, COMP, "FMA", TGSI_OPCODE_FMA },
>>>>>>>> + { 1, 1, 0, 0, 0, 0, COMP, "POPCNT", TGSI_OPCODE_POPCNT },
>>>>>>>> + { 1, 1, 0, 0, 0, 0, COMP, "IMSB", TGSI_OPCODE_IMSB },
>>>>>>>> + { 1, 1, 0, 0, 0, 0, COMP, "ILSB", TGSI_OPCODE_ILSB },
>>>>>>>> + { 1, 1, 0, 0, 0, 0, COMP, "UMSB", TGSI_OPCODE_UMSB },
>>>>>>>> + { 1, 1, 0, 0, 0, 0, COMP, "ULSB", TGSI_OPCODE_ULSB },
>>>>>>>> };
>>>>>>>>
>>>>>>>> const struct tgsi_opcode_info *
>>>>>>>> @@ -321,6 +327,11 @@ tgsi_opcode_infer_type( uint opcode )
>>>>>>>> case TGSI_OPCODE_IABS:
>>>>>>>> case TGSI_OPCODE_ISSG:
>>>>>>>> case TGSI_OPCODE_IMUL_HI:
>>>>>>>> + case TGSI_OPCODE_POPCNT:
>>>>>>>> + case TGSI_OPCODE_ILSB:
>>>>>>>> + case TGSI_OPCODE_IMSB:
>>>>>>>> + case TGSI_OPCODE_ULSB:
>>>>>>>> + case TGSI_OPCODE_UMSB:
>>>>>>>> return TGSI_TYPE_SIGNED;
>>>>>>>> default:
>>>>>>>> return TGSI_TYPE_FLOAT;
>>>>>>>> @@ -344,9 +355,14 @@ tgsi_opcode_infer_src_type( uint opcode )
>>>>>>>> case TGSI_OPCODE_SAMPLE_I:
>>>>>>>> case TGSI_OPCODE_SAMPLE_I_MS:
>>>>>>>> case TGSI_OPCODE_UMUL_HI:
>>>>>>>> + case TGSI_OPCODE_POPCNT:
>>>>>>>> + case TGSI_OPCODE_ULSB:
>>>>>>>> + case TGSI_OPCODE_UMSB:
>>>>>>>> return TGSI_TYPE_UNSIGNED;
>>>>>>>> case TGSI_OPCODE_IMUL_HI:
>>>>>>>> case TGSI_OPCODE_I2F:
>>>>>>>> + case TGSI_OPCODE_ILSB:
>>>>>>>> + case TGSI_OPCODE_IMSB:
>>>>>>>> return TGSI_TYPE_SIGNED;
>>>>>>>> case TGSI_OPCODE_ARL:
>>>>>>>> case TGSI_OPCODE_ARR:
>>>>>>>> diff --git a/src/gallium/auxiliary/tgsi/tgsi_opcode_tmp.h b/src/gallium/auxiliary/tgsi/tgsi_opcode_tmp.h
>>>>>>>> index 1ef78dd..cba0975 100644
>>>>>>>> --- a/src/gallium/auxiliary/tgsi/tgsi_opcode_tmp.h
>>>>>>>> +++ b/src/gallium/auxiliary/tgsi/tgsi_opcode_tmp.h
>>>>>>>> @@ -206,6 +206,12 @@ OP13(UCMP)
>>>>>>>>
>>>>>>>> OP12(IMUL_HI)
>>>>>>>> OP12(UMUL_HI)
>>>>>>>> +OP13(FMA)
>>>>>>>> +OP11(POPCNT)
>>>>>>>> +OP11(IMSB)
>>>>>>>> +OP11(ILSB)
>>>>>>>> +OP11(UMSB)
>>>>>>>> +OP11(ULSB)
>>>>>>>>
>>>>>>>> #undef OP00
>>>>>>>> #undef OP01
>>>>>>>> diff --git a/src/gallium/include/pipe/p_shader_tokens.h b/src/gallium/include/pipe/p_shader_tokens.h
>>>>>>>> index 8010902..5ed0c34 100644
>>>>>>>> --- a/src/gallium/include/pipe/p_shader_tokens.h
>>>>>>>> +++ b/src/gallium/include/pipe/p_shader_tokens.h
>>>>>>>> @@ -453,7 +453,14 @@ struct tgsi_property_data {
>>>>>>>> #define TGSI_OPCODE_IMUL_HI 180
>>>>>>>> #define TGSI_OPCODE_UMUL_HI 181
>>>>>>>>
>>>>>>>> -#define TGSI_OPCODE_LAST 182
>>>>>>>> +#define TGSI_OPCODE_FMA 182
>>>>>>>> +#define TGSI_OPCODE_POPCNT 183
>>>>>>>> +#define TGSI_OPCODE_IMSB 184
>>>>>>>> +#define TGSI_OPCODE_ILSB 185
>>>>>>>> +#define TGSI_OPCODE_UMSB 186
>>>>>>>> +#define TGSI_OPCODE_ULSB 187
>>>>>>>> +
>>>>>>>> +#define TGSI_OPCODE_LAST 188
>>>>>>>>
>>>>>>>> #define TGSI_SAT_NONE 0 /* do not saturate */
>>>>>>>> #define TGSI_SAT_ZERO_ONE 1 /* clamp to [0,1] */
>>>>>>>> --
>>>>>>>> 1.8.5.2
>>>>>>>>
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>>>>>>
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