Ideally this would be hooked up by ir_print_visitor dumping into a
string that we could include as prog_instruction->Comment when in
debug mode, and not try keeping ir_instruction trees around after
conversion to Mesa. The ir_print_visitor isn't set up to do that for
us today.
There are major missing pieces here. Most operations aren't
supported. Matrices need to be broken down to vector ops before we
get here. Scalar operations (RSQ, RCP) are handled incorrectly.
Arrays and structures are not even considered.
