    1. store_src_rg                   xy = src.rg
    2. init_lane_masks                CondMask = LoopMask = RetMask = true
    3. zero_slot_unmasked             $0 = 0
    4. copy_constant                  $1 = 0x3F800000 (1.0)
    5. zero_slot_unmasked             $2 = 0
    6. copy_constant                  $3 = 0x3F800000 (1.0)
    7. load_src                       src.rgba = $0..3