Peter Alexander:
> void foo(int x)
> {
> int[10] a;
> foreach (ref e; a)
> e = bar(x);
> }
>
> If bar is pure then you can safely transform this into:
>
> void foo(int x)
> {
> int[10] a;
> auto barx = bar(x);
> foreach (ref e; a)
> e = barx;
> }
If bar is pure, but it throws exceptions, the two versions of the code behave
differently, so it's a wrong optimization. You need bar to be pure nothrow.
Moving pure nothrow functions out of loops is an easy optimization, and even
simple D compilers are meant to do it. Aggressively optimizing D compilers are
also free to memoize some results of pure (and probably nothrow too) functions.
-------
Regarding the discussion about virtual functions, show me a D compiler able to
de-virtualize very well, as the Oracle JVM does :-)
Time ago I have asked LLVM devs to improve this situation for LDC, they have
now fixed most of my bug reports, so I think they will eventually fix this too
(maybe partially):
http://llvm.org/bugs/show_bug.cgi?id=3100
Bye,
bearophile
