MAX_IMM_TYPE_BITS
BUILD_BUG_ON(MAX_IMM_PAYL_BITS + MAX_IMM_TYPE_BITS != 32);
BUILD_BUG_ON(RTRS_LAST_IMM > (1<<MAX_IMM_TYPE_BITS));
MAX_IMM_TYPE_MASK = ((1 << MAX_IMM_TYPE_BITS) - 1),