[Bug tree-optimization/55060] False un-initialized variable warnings

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55060

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-10-25
                 CC|                            |jamborm at gcc dot gnu.org
     Ever Confirmed|0                           |1

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> 2012-10-25 11:22:40 UTC ---
At the point of the early uninit pass it sees:

main (int argc, char * * argv)
{
  int i;
  int D.1716;
  int i.0;

<bb 2>:
  a.isra.0 ();
  # VUSE <.MEM_3(D)>
  i.0_1 = i;
  b.isra.1 ();
  D.1716_2 = 0;
  # .MEM_4 = VDEF <.MEM_3(D)>
  i ={v} {CLOBBER};
  # VUSE <.MEM_4>
  return D.1716_2;

thus a read from the memory location 'i' which is uninitialized.  Dead code
elimination has not yet removed that read (i.0_1 is unused after all).

I'd say the literal presence of b (i) is considered a use of i in C-terms,
thus the warning is not really incorrect.

That IPA-SRA has this side-effect on the otherwise still unoptimized
body of main is bad - early uninit was put before early inlining for a reason
and now IPA-SRA defeats this ... can we make it more "IPA" like and
have an explicit local transform stage?