It isn't. You'd need full lifetime analysis as part of the compiler to even decide whether you _could_ skip the allocation, and even then it's 100% up to the ci

It isn't. You'd need full lifetime analysis as part of the compiler to even decide whether you _could_ skip the allocation, and even then it's 100% up to the circumstance and actual lifetime of the data to say whether it can be, e.g. stack-allocated to avoid placing it somewhere less localized.