You shouldn't have to pay that much. Pipes give you almost nothing, so they should cost almost nothing.

Specifically, there aren't many reasons for your fastest IPC to be slower than a long function call.

If you don't think pipes offer much, don't use them.

Saying "long function call" doesn't mean much since a function can take infinitely long.

A long distance function call, that invalidates everything on your cache.

…which is quite expensive.

Yes, it is. But it's much cheaper than interacting by pipe.

Linux is optimizing sockets with a similar goal. And it's quite far on that direction. But there's still some margin to gain.

Pipes don’t exist for safety, they exist as an optimization to pass data between existing programs.

NOT writing and reading to and from a file stored on a drive is not, in this context, an optimization, but a significantly freeing conceptual shift that completely transforms how a class of users conducts themselves when using the computer.

The safety is memory protection. If you don't care about memory protection, you can reduce IPC to passing pointers around.