Why libphobos2.a?

[Walter Bright]

Graham Fawcett wrote:
> Newbie question: if the D compiler (a) is very fast and (b) can
> optimize application code when it has access to all library sources,
> then isn't libphobos2.a a premature optimization? Why have it at all,
> when the Phobos sources are available?

The global optimization at the moment is limited to inlining. Most functions are 
not inlinable.