[uyt]

> Kernel developers obsess about speed and performance. The Linux kernel is built using -mregparm=3, which is sometimes called fastcall.

I've never messed with calling convention for the sake of performance before so I found this bit interesting. I found more info about it at: https://en.wikipedia.org/wiki/X86_calling_conventions#Borlan...

Does anyone have benchmarks? Assuming I don't care about ABI stability, what's the fastest calling convention?

[krona]

> Assuming I don't care about ABI stability, what's the fastest calling convention?

I'd assume a modern optimizing compiler will, in situations where it's permitted, create completely novel calling conventions depending on the situation. Whole program optimization is one area you might see this.

[rocqua]

The compiler tends to be limited in how it can change calling conventions by external visibility of the functions. Generally if you compile a function down to an object file the compiler will want to make that object file linkable with any other object files importing that symbol properly.

Whole program optimization gives the compiler some ways around that. I am not sure how much freedom it gives the compiler.