load_reg is something like load_payload except it has a single
source. It copies the entire source to the destination. Its purpose is
to convert a non-SSA VGRF into an SSA value. This copy is marked as
volatile so that it will act as a scheduling barrier.
v2: Fix some typos in the commit message. Eliminate the
brw_builder::LOAD_REG overload that returns a brw_inst*. This is
unlikely to ever be used. Add some checks to brw_validate. All
suggested by Caio.
v3: Force the source and destination types of the LOAD_REG to by
integer. This will (eventually) simplify the creating of unit tests for
the pass that adds LOAD_REG instructions.
Reviewed-by: Caio Oliveira <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31497>
