[Mesa-dev] [PATCH 4/9] gallium-tgsi: add TGSI_OPCODE_{FMA-POPCNT-MSB-LSB} description
Roland Scheidegger
sroland at vmware.com
Tue Jan 7 11:20:08 PST 2014
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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