Alyssa Rosenzweig
4f7cae5e61
In https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35802 we will significantly rework geometry shaders & transform feedback. In the new approach, transform feedback is executed as part of the hardware vertex shader, meaning the vertex shader needs to write out all the "copies" of the same value into different parts of the XFB buffer. In the general case of a GS writing triangle strips, we get 0-3 copies. This is good and lets us parallelize XFB better with GS. In the case of a VS alone with XFB, we insert a passthrough GS. In that case special case, we can only get at most 1 copy, so if we can prove the length of the output strip is 3 we can delete 2/3 of the shader. Anyway, the only thing preventing NIR from doing that optimization is failing to see through some conditionals, fixed by optimizing with the law of trichotomy. We could add other variants of this pattern (signed vs unsigned, iand vs ior/ixor) if we expect anything else to hit this other than my boutique use case. Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io> Reviewed-by: Marek Olšák <maraeo@gmail.com> Reviewed-by: Mary Guillemard <mary.guillemard@collabora.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35802>
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