Hi
> > > You mean shared libraries without the opportunity to
> inline library code?
> > > This would result in a huge performance loss, I think.
> >
> > Usually _mild_ performance loss, in exchange for major code-size
> > savings, I would think. C obviously has worked quite fine under
> > exactly this restraint (though C implementations obviously aren't
> > built to take as great advantage of inlining library code
> as Haskell may be).
>
> I think that the performance loss is much higher in the case
> of Haskell because of Lazy Evaluation, massive use of higher
> order functions and possibly more.
Example 1:
foo x | "test" `isPrefixOf` xs = ...
| otherwise = ...
If you have cross-module inlining, you get the rather obvious if like
construct. If you don't, you have to evaluate otherwise and test its
value.
Example 2:
(a :: Int) + b
If you have cross-module specialisation you get a primitive integer
arithmetic instruction (possibly with a bit of unboxing, although often
not). If you don't, you get a dictionary lookup, followed by a higher
order application.
One reason cross-module inlining is essential is that many Haskell
functions don't do very much, think of (+), (||), (>>), not, otherwise
etc. In C these would be built-in's, so are always available to the
optimiser (and usually just one instruction), in Haskell you need to get
them from the Prelude.
Thanks
Neil
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