[Bug tree-optimization/49513] DOM inhibits if-conversion and vectorization

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49513

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |law at gcc dot gnu.org
            Summary|PRE inhibits if-conversion  |DOM inhibits if-conversion
                   |and vectorization           |and vectorization

--- Comment #3 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-06-23 12:58:44 UTC ---
(In reply to comment #2)
> thanks for the fast analysis.
> 
> the code in question was there also to test what the vectorized code would do
> for x=0 and y=0 (it is extracted from a simplified version of atan2f that gcc
> can vectorize).
> Being a test, I can workaround (I've to test extreme conditions explicitely
> anyhow).
> 
> In any case I think that any peeling will ruin alignmement.
> 
>  hoping gcc can find ways to avoid PRE and vectorization to clash.

I had a closer look and it is DOM jump-threading which creates this
rotated loop.  CCin Jeff who was working in this area - PRE avoids
this kind of transformation.  Jeff - can we avoid threading through
the loop header somehow?