On 23.08.2017 16:03, Roland Scheidegger wrote:
Am 23.08.2017 um 15:49 schrieb Ilia Mirkin:
On Wed, Aug 23, 2017 at 9:20 AM, Nicolai Hähnle <nhaeh...@gmail.com> wrote:
On 22.08.2017 16:56, Ilia Mirkin wrote:
On Tue, Aug 22, 2017 at 10:51 AM, Roland Scheidegger <srol...@vmware.com>
wrote:
I am probably missing something here, but why do you need a new register
file? Since you couldn't use LOAD with TGSI_FILE_CONSTANT before, can't
you just allow LOAD with TGSI_FILE_CONSTANT and achieve the same thing?
Or do you need to know how it's going to be accessed in advance?
With bindless, LOAD can take a CONST I believe [which contains the
value of the bindless id]. I think it's nice to keep those concepts
separate... having CONST sometimes mean the value and other times mean
the address is a bit weird. This way CONSTBUF[0] is the address of the
0th constbuf.
I'm still not quite convinced. The levels of indirection should clarify the
meaning, shouldn't they?
You get
LOAD dst, CONST[0][0], IMM[0]
when loading from offset IMM[0] of a bindless buffer whose handle is at the
beginning of the buffer CONST[0].
You get
LOAD dst, CONST[0], IMM[0]
when loading from offset IMM[0] of non-bindless buffer 0.
Is there ever really a situation where the two could be confused?
I always considered CONST[0] == CONST[0][0]. Technically they're not,
since once has the second dimension in the TGSI encoding while the
other doesn't. But practically,
MOV TEMP[0], CONST[0]
and
MOV TEMP[0], CONST[0][0]
are in every way identical. Currently st/mesa will just use CONST[0]
everywhere, never adding the 2nd dimension.
Maybe it would be worth the effort to fix this?
Would be nice. One thing that makes this a bit awkward is that older
drivers just don't support two-dimensional CONST at all -- see
PIPE_SHADER_CAP_MAX_CONST_BUFFERS. Giving them a shader that loads
CONST[0][n] is going to fail.
Basically, changing this is a backward-compatible change to state
trackers, which would have to promise not to produce one-dimensional
CONST for the usual, vec4-based constant fetching.
On the other hand, maybe we're over-complicating this. The only
instruction that is really affected is LOAD. And for LOAD, there
shouldn't be a compatibility problem. Hmm...
Cheers,
Nicolai
Roland
As such, I don't think we
should start having behavioural differences for those on some
instructions.
--
Lerne, wie die Welt wirklich ist,
Aber vergiss niemals, wie sie sein sollte.
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