[Compiler Bug]: Compiler incorrectly removes memoization of an expensive operation in useMemo about react

[poteto]

Yeah the compiler currently does type inference to determine if something should be memoized or not. In this case, we don't memoize primitives as you show in your first example as the + operator makes the compiler assume that expensive(a) produces a primitive, which is always going to be referentially equal. I think the challenge here is that the compiler doesn't know that expensive() is expensive so if we apply memoization to primitive producing call expressions as well this would probably greatly increase the number of memo slots we use in the cache.

[issacgerges]

Ah, I see @poteto, thanks

I guess the thought is that memoization should be in expensive instead of react? This example also erases memorization, and the return value is a primitive but not necessarily cheap to produce.

(sorry this is sorta convoluted)

  const isNotPrime = useMemo(() => {
    const isPrime = checkIfPrime(a);
    return !isPrime
  }, [a])

I wonder if the compiler could/should "respect" the memorization provided if decides none is necessary. I'm sure these problems are more complicated than I'm giving them credit! Feel free to close if this is an intentional design decision

[kaaboaye]

Same issue as #29172 and #29580