Ballot intrinsics return a bitfield of subgroups. In GLSL and some
SPIR-V extensions, they return a uint64_t. In SPV_KHR_shader_ballot,
they return a uvec4. Also, some back-ends would rather pass around
32-bit values because it's easier than messing with 64-bit all the time.
To solve this mess, we make nir_lower_subgroups take a new parameter
called ballot_bit_size and it lowers whichever thing it gets in from the
source language (uint64_t or uvec4) to a scalar with the specified
number of bits. This replaces a chunk of the old lowering code.
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
This commit pulls nir_lower_read_invocations_to_scalar along with most
of the guts of nir_opt_intrinsics (which mostly does subgroup lowering)
into a new nir_lower_subgroups pass. There are various other bits of
subgroup lowering that we're going to want to do so it makes a bit more
sense to keep it all together in one pass. We also move it in i965 to
happen after nir_lower_system_values to ensure that because we want to
handle the subgroup mask system value intrinsics here.
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
