[Bug rtl-optimization/49330] Integer arithmetic on addresses optimised with pointer arithmetic rules

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49330

--- Comment #7 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2011-06-10 09:50:28 UTC ---
The alias.c machinery is clearly based on the fundamental assumption of pointer
arithmetics, i.e. that you aren't allowed to compute a difference unless both
pointers point to the same enclosing object.  The testcase is a nice attempt at
smuggling the violation of this rule behind a uintptr_t based manipulation.

Not clear what to do IMO.  Richard is proposing to leverage the escape sites:

  px_1 = (uintptr_t) &x;
  py_2 = (uintptr_t) &y;

but this will pessimize.  Ideally we should leverage the one problematic line:

  p.2_6 = (int *) p_5;

which creates the pointer out of the integer, but it has already disappeared in
the very first RTL representation.