Why are globals set to tls by default? and why is fast code ugly by default?

[ryuukk_]

On Sunday, 26 March 2023 at 19:08:32 UTC, Steven Schveighoffer 
wrote:
> On 3/26/23 2:07 PM, ryuukk_ wrote:
>> Hi,
>> 
>> It's common knowledge that accessing tls global is slow 
>> http://david-grs.github.io/tls_performance_overhead_cost_linux/
>> 
>> What i do not understand is the reasoning behind choosing tls 
>> global by default in D
>
> If you know a variable is not `shared`, then you know it can 
> only be accessed from the current thread. This has huge 
> implications for thread access.
>
> However, one problem that D has no good solution is passing 
> thread-local data to another thread (to be owned by the new 
> thread, and no access in the current thread). That's typically 
> the most common use case for "shared data".
>
> -Steve

I haven't explored this use case, that must explain why i find it 
surprising, however, i read about other languages too, and they 
seem to be explicit whenever they make use of TLS

C, C++, Rust, Zig, Go doesn't do TLS by default for example