On Monday, May 7, 2018 8:53:34 AM PDT Jason Ekstrand wrote: > On Mon, May 7, 2018 at 8:02 AM, Alejandro Piñeiro <apinhe...@igalia.com> > wrote: > > > Hi Jason, > > > > as part of the ARB_gl_spirv work, we are doing the linking based on the > > nir shader that comes from spirv_to_nir. On some cases, > > nir_lower_wpos_ytransform introduces a new uniform, > > "gl_FbWposYTransform". So as the uniform is there when we start to do > > the linking, it is treated as any other uniform, being added to the > > UniformStorage, accessible through the OpenGL API and so on. Something > > that I understand that we don't want. On GLSL this is not a problem > > because the linking is done based on MESA/IR, then the IR is converted > > to NIR, and the lowering adds the uniform based on the NIR shader, > > really after the linking. > > > > The first solution I thought was just mark the uniform with a special > > location [1]. It would need to be a negative value, not -1 that is > > already reserved for not-assigned locations (we still have some cases > > for those, even if in general ARB_gl_spirv makes explicit location > > mandatory). So it would be a new negative value, like lets say -5. So > > then on the linking, if the uniform location has this value, the uniform > > is skipped. > > > > After checking that this solution worked (although I only tested with > > some tests), I started to search for an alternative, as this solution > > seemed too hacky. > > > It does seem a bit hacky, yes. > > > > But this lowering needs to be run before nir_lower_io, > > and nir_lower_io is part of the uniform lowering. So I didn't see really > > reasonable to do a nir_lower_io without nir_lower_wpos_ytransform, do > > the linking, and then execute again nir_lower_io/nir_lower_wpos_transform. > > > > This is all a bit sticky. One observation is that the newly added uniform > makes usage of the token system. Are tokens no longer used with SPIR-V? I > guess they are kind-of an old mechanism to handle the crufty ARB program > parameters. However, you could have -5 mean "It uses a token" > > Another option would be to use a system value instead of a uniform. We can > then convert it to a uniform in the back-end. We have a few places where > we do things like this for compute shaders. > > I don't have a lot of good ideas or strong opinions, I'm afraid. :-( Maybe > Ken has some? > > --Jason
In GLSL IR, we use var->how_declared == ir_var_hidden to hide internally created variables from API introspection. Why not just port something similar over to the newer NIR code? --Ken
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