Like with casts, we need to subtract the cost of `lshr` instruction

from budget, and recurse into LHS operand.

Seems "pretty obviously correct" to me?

To be noted, there is a number of other shortcuts we *could* cost-model:

`... + (-1 * ...)`->`... - ...`<- likely very frequent case`x - (rem x, power-of-2)`, which is currently`(x udiv power-of-2) * power-of-2`->`x & -log2(power-of-2)``rem x, power-of-2`, which is currently`x - ((x udiv power-of-2) * power-of-2)`->`x & log2(power-of-2)-1``... * power-of-2`->`... << log2(power-of-2)`<- likely not very beneficial