[tialaramex]

As pointed out elsewhere in this comment tree, things living on the stack when they needn't can mean they don't fit and thus the program doesn't work, so the optimisation can matter for that reason, and this is a particular reason to worry about it for larger objects where the optimiser is more likely not to see what's going on.

[msbarnett]

And yet, real world production rust programs exist and measured performance is generally excellent.

People are acting like this graph they saw for the first time today means that Rust is running at sub-Ruby speeds, when even with these excess copies we already know, and have known for years how rust programs have been performing in real life.

That there is room for improvement here does not mean that the status quo was not already excellent.

[germandiago]

> People are acting like this graph they saw for the first time today means that Rust is running at sub-Ruby speeds

Well, this is no different of how Rust people talk about C++ as if it was as unsafe as if you were writing inline assembly :)