[Bug rtl-optimization/37516] ~(-2 - a) is not being optimized into a + 1

["rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37516

--- Comment #3 from rguenther at suse dot de <rguenther at suse dot de> 2012-02-23 08:47:55 UTC ---
On Thu, 23 Feb 2012, pinskia at gcc dot gnu.org wrote:

> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37516
> 
> Andrew Pinski <pinskia at gcc dot gnu.org> changed:
> 
>            What    |Removed                     |Added
> ----------------------------------------------------------------------------
>              Status|UNCONFIRMED                 |ASSIGNED
>    Last reconfirmed|                            |2012-02-23
>          AssignedTo|unassigned at gcc dot       |pinskia at gcc dot gnu.org
>                    |gnu.org                     |
>      Ever Confirmed|0                           |1
> 
> --- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-02-23 08:42:01 UTC ---
> I have an idea on how to fix this.
> basically:
> ~(C - X)
> is the same as:
> ~ - (X - C)
> which then can be simplified to
> X - (C+1)
> 
> This should be done on both the tree level (on the pinskia/treecombine branch
> in tree-ssa-fold.c) and the rtl level in simplify-rtx.c.

Maybe get away with these old-stylish names ('tree' and 'fold') and
make it match reality, gimple-ssa-combine.c ;)

Still have to have a look at your branch - do you have a brief
overview documentation, for example on the wiki?  What I'd like
to do is have an interface that I can re-use for VN combining,
basically replace its simplify_*_expression functions.

Richard.