Hello Peter, On Fri, 19 Apr 2019 10:11:43 +0100 Peter Sewell <peter.sew...@cl.cam.ac.uk> wrote:
> On 19/04/2019, Jakub Jelinek <ja...@redhat.com> wrote: > > On Fri, Apr 19, 2019 at 10:19:28AM +0200, Jens Gustedt wrote: > [...] > > That penalizes quite a few optimizations though. > > If you have > > ptr != ptr2 > > and points-to analysis finds a set of variables ptr as well as ptr2 > > points to and the sets would be disjoint, it would be nice to be > > able to optimize that comparison away (gcc does); similarly, if one > > of the pointers is &object or &object + sizeof (object). > > By requiring what you request above, it can be pretty much never > > optimized, unless the points-to analysis is able to also record if > > the pointer points to the start, middle or end of object and only > > if it is known to be in the middle it can safely optimize, for > > start or end it would need to prove the other pointer is to end or > > start and only non-zero sized objects are involved. > > A possible compromise position might be to make it > implementation-defined whether round-trip casts of a one-past pointer > into integer and back preserve provenance. I don't know whether > that corner case crops up in real code... Wouldn't that impose to keep track of some provenance information in integers? Jens -- :: INRIA Nancy Grand Est ::: Camus ::::::: ICube/ICPS ::: :: ::::::::::::::: office Strasbourg : +33 368854536 :: :: :::::::::::::::::::::: gsm France : +33 651400183 :: :: ::::::::::::::: gsm international : +49 15737185122 :: :: http://icube-icps.unistra.fr/index.php/Jens_Gustedt ::
pgpchhr4r7S_a.pgp
Description: Digitale Signatur von OpenPGP
