Also if the data is being copied into userspace anyway, then it's quite fast to check that memory is zero. There's no C "primitive" for this, but all C compilers can turn a simple loop into relatively efficient assembler[1].
If you're using an API that never copies the data into userspace and you have to read from a pipe, then yes sparse detection will be much more expensive.
In either case it should save disk space for core files which are highly sparse.
