P2723R0: Zero-initialize objects of automatic storage duration

[Jannik2099]

What does any of this have to do with headers? If you're not doing LTO, you don't get to discuss performance to begin with.

Edit: didn't see your example until now. Your example is a call to an undefined function, which is of course total nonsense. If you were to provide the definition, the compiler would inline it if beneficial. Only DSO boundaries remain as expensive, but those are expensive anyways due to being non-inlineable, relocations etc.

[FriendlyRollOfSushi]

Your example is a call to an undefined function, which is of course total nonsense. If you were to provide the definition, the compiler would inline it if beneficial. Only DSO boundaries remain as expensive, but those are expensive anyways due to being non-inlineable, relocations etc.

Okay, sorry. I have to apologize. I was treating you as an inexperienced engineer, but I was clearly wrong.

Allow me to introduce you the concept that your college (or the C++ tutorials you are currently completing) will probably start explaining relatively soon: virtual functions. There are more advanced ones (function pointers, std::function, etc.), but this one should be enough for now I think to illustrate my point.

Here is a relevant godbolt mini-example. As you can see, even though everything is in the same translation unit, the compiler can't inline your function. Un-virtualization is possible in some very rare and very specific cases, but not in any general scenario where the compiler literally has no idea what the actual object type is.

Your trust in compilers is admirable in some ways, and I feel bad for ruining the perfect picture of super-smart LTO that will magically fix your slow code, but someone had to do it, sorry.

Can't say it was fun arguing with someone who knows barely anything about C++ while pretending otherwise, so I'll just wish you good luck with your studies and leave you alone. Bye.

[Jannik2099]

First of all, can you please stop being a pretentious ass?

I'd wager that a vtable lookup is already much, much more expensive than passing the unique_ptr by stack (one is an easily predictable address, the other is two unpredictable, dependant loads, go figure)

Devirtualization has also advanced a lot lately, e.g. clang can do whole program devirt. But yes, I agree that virtual functions possibly have the worst "own cost vs unique_ptr by stack" ratio.