[Bug ipa/111773] Inconsistent optimization of replaced operator new()

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111773

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |UNCONFIRMED
     Ever confirmed|1                           |0
           Assignee|rguenth at gcc dot gnu.org         |unassigned at gcc dot gnu.org

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
So the second example is fixed, but it's quite a corner-case so probably not
worth backporting.  Given we have a single bugreport for two issues back to
UNCONFIRMED for the first issue.

I agree with Andrew _that_ issue behaves within the constraints of the
standard.
ISTR it says that 'operator new' has to return a pointer that nothing else
points to which means it acts as if it were restrict qualified.  That allows
GCC to conclude x != 0 because it rewrites x == 0 as a - p == 0 and
a == p.  The difference operation cannot be constant folded based on this
but during IPA optimization we inline 'new' which exposes p == a and thus
a - p == 0.