[Mesa-dev] [PATCH] ir_to_mesa: do not check the number of uniforms against hw limits

[José Fonseca]

On Mon, 2011-03-14 at 11:23 -0700, Brian Paul wrote:
> On 03/12/2011 07:44 PM, Marek Olšák wrote:
> > The r300 compiler can eliminate unused uniforms and remap uniform locations
> > if their number surpasses hardware limits, so the limit is actually
> > NumParameters + NumUnusedParameters. This is important for some apps
> > under Wine to run.
> >
> > Wine sometimes declares a uniform array of 256 vec4's and some Wine-specific
> > constants on top of that, so in total there is more uniforms than r300 can
> > handle. This was the main motivation for implementing the elimination
> > of unused constants.
> >
> > We should allow drivers to implement fail&  recovery paths where it makes
> > sense, so giving up too early especially when comes to uniforms is not
> > so good idea, though I agree there should be some hard limit for all drivers.
> 
> I added the check_resources() code to fix an issue with the SVGA 
> driver.  If we can't do resource checking against the 
> ctx->Const.Vertex/FragmentProgram limits we need something else.
> 
> In Gallium we have the PIPE_SHADER_CAP_MAX_x queries.  Are you saying 
> we shouldn't check shaders against those limits either?
>
> If we were to push all the shader resource checking down into the 
> Gallium drivers we'll need a new way to propagate error messages back 
> to the user (we can only return NULL from create_X_state() now). 
> Another other problem would be instituting consistant error reporting 
> across all the drivers.
> 
> We've kind of tiptoed around this issue in the past.  It's probably 
> time to come up with some real solutions.

Not only some drivers are able to optimize away declared-yet-unused
registers; but other drivers drivers may actually need to add extra
temps/const regs to implement certain opcodes/state. Both issues make it
difficult to make guarantees around PIPE_SHADER_CAP_MAX_x, as we can
easily end up advertising too little or too much.

It looks there's not much alternative to mimicking GLSL here, i.e.,
advertise these as limits but allow concrete shaders to pass/fail to
compile on a case-by-case basis.

I'm not sure what's the best what to convey errors from the drivers: to
return pipe_error and extend it to include things like  
    PIPE_ERROR_TOO_MANY_CONSTS
    PIPE_ERROR_TOO_MANY_TEMPS
    PIPE_ERROR_TOO_MANY_INSTRUCTIONS
    etc.
and translate them in the state tracker; or use message strings. At a
glance, it looks like an error enum would be expressive enough for most
stuff. 

Jose