Cranked bars / Bent up bars are provided on top of the reinforcement to resist negative bending moment/Hogging at the supports of the slab.
To resist the shear force at the supports.
Bottom Reinforcement resists the positive bending moment/sagging at the midspan of the slab.
Top Reinforcement resisits the negative bending moment at the supports of the slab.
(Here you can observe ,only alternate bars are cranked)
Unfortunately,IS 456:2000 does not give any clear cut guidance about the bar bending and cutoff details.
If it helped then upvote. This keeps me motivated to write even more.