[Bug tree-optimization/36115] [4.2 Regression] wrong code generated with optimization on x86-64

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2008-05-03 09:32 -------
Confirmed.  On the tree level we get aliasing wrong again:

<bb 2>:
  #   VUSE <n_50>;
  D.30804_7 = n;
  #   VUSE <SMT.294_51>;
  D.30805_8 = s_3->x;
  if (D.30804_7 < D.30805_8) goto <L3>; else goto <L5>;

<L3>:;
  __b_9 = &s_3->x;

  # __b_2 = PHI <__b_9(3), &n(2)>;
<L5>:;
  #   VUSE <n_50>;
  #   VUSE <D.30570_14>;
  D.30813_12 = *__b_2;
  #   D.30570_15 = V_MUST_DEF <D.30570_14>;
  D.30570 = 2;
  if (D.30813_12 > 2) goto <L6>; else goto <L8>;

<L6>:;
  __b_20 = &s_3->x;

  # __b_1 = PHI <__b_20(5), &D.30570(4)>;
<L8>:;
  #   VUSE <n_50>;
  #   VUSE <D.30570_15>;
  D.30636_23 = *__b_1;

DSE deleted the intermediate store to s_3->x:

   #   VUSE <n_50>;
   #   VUSE <D.30570_14>;
   D.30813_12 = *__b_2;
-  #   SMT.294_52 = V_MAY_DEF <SMT.294_51>;
-  s_3->x = D.30813_12;
   #   D.30570_15 = V_MUST_DEF <D.30570_14>;
   D.30570 = 2;

thus, a workaround is -fno-tree-dse.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
          Component|target                      |tree-optimization
     Ever Confirmed|0                           |1
           Keywords|                            |alias, wrong-code
      Known to work|4.1.3                       |4.1.3 4.3.0
   Last reconfirmed|0000-00-00 00:00:00         |2008-05-03 09:32:16
               date|                            |
            Summary|wrong code generated with   |[4.2 Regression] wrong code
                   |optimization on x86-64      |generated with optimization
                   |                            |on x86-64
   Target Milestone|---                         |4.2.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36115