Optimization beyond the Module Border

[Malcolm Wallace]

> I'd be interested in any progress here -- we noticed issues with
> optimisations in the stream fusion package across module boundaries
> that we never tracked down. If there's some key things not firing,
> that would be good to know.

I suspect that if all modules are compiled -O0, then you recompile one
module with -O2, high up in the dependency graph (i.e. it depends on
many lower-level modules), plus all things that in turn depend on it
(--make), you will not get the good performance you expect.  None of the
lower-level functions will have exported inlinings or fusion rules into
the interface file.  _All_ modules must be recompiled with -O2,
especially the bottom of the dependency chain, to get the best benefit
from optimisation.

Regards,
    Malcolm