[LLVMdev] PredicateSimplifier questions

[Chris Lattner]

On Feb 15, 2009, at 10:08 PM, John Regehr wrote:

>> Predsimplify is believed to have bugs (it results in miscompiled
>> programs) and certainly isn't efficient (it was written before much  
>> of
>> include/ADT). Finally, predsimplify is likely to go away once I or
>> someone else writes a proper VRP pass.
>
> Whoever does this, I strongly encourage looking into using (or at  
> least
> providing optional support for) the Apron library:
>
>   http://apron.cri.ensmp.fr/library/
>
> No sense reinventing these wheels.

In my experience, starting with a very simple and very cheap approach  
will get most of the benefit.  For those who really want to eliminate  
every check possible, a more expensive approach can be used on top of  
it.  If someone is interested in array bound check elimination, I'd  
suggest starting with the ABCD (array bounds check elimination on  
deman) paper.  I believe that vmkit would hugely benefit from this as  
well.

-Chris