[Bug middle-end/67662] -fsanitize=undefined cries wolf for X - 1 + X when X is 2**30

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67662

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-09-21
          Component|sanitizer                   |middle-end
     Ever confirmed|0                           |1

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This is a reassociation issue inside fold-const.  Basically we change x - 1 + x
to x + x - 1 which is invalid as it introduces an overflow which was not there
before.  (This is why we need an addition tree where overflow is defined).