Kagamin:
Calling convention optimizations can probably be done during whole program optimization, which 1) usable for computation-intensive applications anyway, 2) guarantees invisibility of those fastcall functions to external code so there's no incompatibility.
In D you can tag a free function as "private", to make them module-private. Maybe in this case the D compiler is free to use any kind of calling convention for them.
Bye, bearophile
