Halt is like a return for the entire shader or exit() if you prefer to
think of it that way. Once an invocation hits a halt, it's 100% dead.
Any writes to output variables which happened before the halt do,
however, still apply.
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7356>
Jason Ekstrand
630e54a08b