[AnthonyMouse]

> when many C++ and Rust programs are about to end, they spend the last few cycles uselessly deallocating memory that would've immediately been freed via _exit(2)

This isn't useless because memory allocation can happen during destruction/exit, e.g. to write some data to the filesystem.

Suppose you have a container with a billion objects. The container's destructor iterates over each object, doing some housekeeping that requires making a copy and then deleting the original before moving on to the next object.

That requires memory equivalent to one additional object because an original is destroyed following each copy. Stop dellocating memory during destruction/exit and the total memory required doubles, because you have all the copies but still all the originals.

There are also some helpful things that happen during deallocation. For example, glibc has double free detection, which strongly implies potential UAF but it's only detected if the second free() actually gets called.