Bug 109573

I looked into this for a few hours today, it's unfortunately a bit more complicated than I'd hoped.  My patch is correct, it's just exposing a pre-existing issue.

That test has a single SPIR-V module containing multiple shader stages.  When compiling that module, we generate shader inputs and outputs for every stage...in a NIR shader targeting a particular shader stage.  So, we suddenly have VS output variables in a TCS.  The TCS expects outputs to be per-vertex arrays (or marked patch).  VS outputs are not.  So, they are illegal in a TCS.

In particular, there is a gl_PerVertex output variable for another stage in the TCS, which is being structure split, giving us top-level output for clipdist[x] and culldist[x].  But in a TCS, those would need an extra dimension - dist[x][y].  The validator tries to enforce that variables marked 'compact' must be arrays, and after unwrapping the per-vertex IO array dimension, it sees simply 'float', which is rightly illegal.

I'm testing a patch to remove dead input/output variables at the end of spirv_to_nir(), which should eliminate the invalid ones before the validator ever sees the shenanigans.  Jason recommended this, and we take a similar approach already in some cases.

MR 215 opened: https://gitlab.freedesktop.org/mesa/mesa/merge_requests/215

fixed by

origin/master 6775665e5eec7db3f291508a8b7ba2a792f62ec0
Author:     Kenneth Graunke <kenneth@whitecape.org>

spirv: Eliminate dead input/output variables after translation.

spirv_to_nir can generate input/output variables which are illegal
for the current shader stage, which would cause nir_validate_shader
to balk.  After my recent commit to start decorating arrays as compact,
dEQP-VK.spirv_assembly.instruction.graphics.module.same_module started
hitting validation errors due to outputs in a TCS (not intended for the
TCS at all) not being per-vertex arrays.

Thanks to Jason Ekstrand for suggesting this approach.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109573
Fixes: ef99f4c8d17 compiler: Mark clip/cull distance arrays as compact before lowering.