The SB back-end optimizer for the mesa R600g driver corrupts the vertex shader for widget drawing. This will not be fixed upstream because SB is getting replaced as part of the new NIR path. This was thought to be an issue with instancing and an attempted fix was submitted in D8374, but it did not fix the issue. This patch reimplements the array look-up part of the code using switch case as a workaround and removes the old workaround implemented as part of D8374. Reviewed By: Clement Foucault Differential Revision: https://developer.blender.org/D10967