Re: LLVM--Low Level Virtual Machine--and Ada

[Duncan Sands <baldrick@free.fr>]

> > PS: the only thing that needed new LLVM functionality,
> > i.e. functionality that didn't exist and wasn't being
> > worked on, was pointers to nested functions.
> 
> How did you implement those?
> 
> GNAT uses trampolines, which are less than ideal
> for several reasons.

Hi Bob, I used trampolines.  I really couldn't do it any other
way without a bunch of modifications to the GNAT front-end.
Also, this seems to be the only solution if you want to be able
to pass such pointers to foreign language routines, which seems
nice to have if not essential.  The major downside I see is that
they seem to be extremely expensive, presumably because you take
an icache hit every time you jump to the stack.  I plan to implement
a bunch of small optimizations which may help, such as converting
direct calls to trampolines into direct calls to the nested functions
(inlining hopefully will create such direct calls).  Any suggestions
for a better approach than trampolines?  I'm also curious to hear
what the other less than ideal properties of trampolines are!

Ciao,

Duncan.