The pass should work for all bit sizes but it's less clear that the extra instructions are worth it on small integers. Also, the hardware doesn't do mul_high on anything other than 32-bit integers and, absent any decent mechanism for testing the pass on 8 and 16-bit types, it's probably best to just leave it disabled for now.
Shader-db results on Sky Lake:
total instructions in shared programs: 15105795 -> 15111403 (0.04%) instructions in affected programs: 72774 -> 78382 (7.71%) helped: 0 HURT: 265
Note that hurt here actually means helped because we're getting rid of integer quotient operations (which are a send on some platforms!) and replacing them with fairly cheap ALU ops.
9ebc00f32e i965: Enable nir_opt_idiv_const for 32 and 64-bit integers
src/intel/compiler/brw_nir.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)