[Mesa-dev] [RFC] Solving the TGSI indirect addressing optimization problem

[Jose Fonseca]

----- Original Message -----
> On Tue, Mar 12, 2013 at 10:31 AM, Christian König
> <deathsimple at vodafone.de> wrote:
> > Am 12.03.2013 02:48, schrieb Marek Olšák:
> >
> >> On Mon, Mar 11, 2013 at 1:44 PM, Christian König
> >> <deathsimple at vodafone.de> wrote:
> >>>
> >>> Hi everybody,
> >>>
> >>> this problem has been open for quite some time now, with a bunch of
> >>> different
> >>> opinions and sometimes even patches floating on the list.
> >>>
> >>> The solutions proposed or implemented so far all more or less incomplete,
> >>> so
> >>> this approach was designed in mind with both completeness and
> >>> compatibility
> >>> with existing code.
> >>>
> >>> Over all it's just an implementation of what Tom Stellard named solution
> >>> #4 in
> >>> this eMail thread:
> >>> http://lists.freedesktop.org/archives/mesa-dev/2013-January/033264.html
> >>
> >> Hi Christian,
> >>
> >> this is definitely not the solution #4. According to the TGSI dump
> >> Christoph posted, it looks more like #3.
> >
> >
> > Well, for me the main difference between proposal #3 and #4 is that #3
> > tries
> > to identify the declaration to use with the supplied "offset", while #4
> > uses
> > a completely distinct identifier for that.
> >
> >
> >> The solution #4 completely changes the temporary file such that it
> >> becomes two-dimensional with the first index being a literal and the
> >> second index being either a literal or ADDR[literal], and it would
> >> always be like that regardless of whether drivers support that or not.
> >> One-dimensional indexing of TEMP is not allowed. For backward
> >> compatibility, the drivers that do not support it would only get a
> >> single array declaration TEMP[0][0..n] and TEMP[0][...] would be
> >> everywhere in the code.
> >
> >
> > Ok, then I misunderstood you a bit, but I don't think the difference is so
> > much.
> >
> > What I'm proposing is that we have an optional "ArrayID" attached to each
> > declaration and refer to this "ArrayID" in the indirect addressing operand.
> > To sum it up declarations should look something like this:
> >
> > DCL TEMP[0..3]        // normal registers
> > DCL TEMP[1][4..11]    // indirectly accessed array
> > DCL TEMP[2][12..15]    // another indirectly accessed array
> > DCL TEMP[16..17] LOCAL    // local registers
> >
> > While an indirect operand might look like this:
> >
> > MOV TEMP[16], TEMP[1][ADDR[0].x-13]
> >
> > On the pro side for this approach is that it is compatible with all the
> > existing state trackers and driver, and we don't need to generate different
> > code depending on weather or not the driver supports this.
> 
> In that case, it would be better to avoid using the operator [] and
> use something else, because it has nothing to do with indexing.

Note that [] operator is also used for const buffer selection.

Jose