I'm not aware of any widespread X86 chips with a line size bigger than 64 bytes. The ISA also practically does have a minimum line size implied by the memory mo

I'm not aware of any widespread X86 chips with a line size bigger than 64 bytes. The ISA also practically does have a minimum line size implied by the memory model, hands waving. My point is that it varies at runtime but the type in the standard is constexpr so you can't actually rely on it unless you actually control where it executes.