*
* Mesa programs (gl_program, not gl_shader_program) have a set of
* flags indicating which varyings are read and written. Computing
* which are actually read from some sort of backend code can be
* tricky when variable array indexing involved. So this pass
*
* Mesa programs (gl_program, not gl_shader_program) have a set of
* flags indicating which varyings are read and written. Computing
* which are actually read from some sort of backend code can be
* tricky when variable array indexing involved. So this pass