[Bug tree-optimization/54498] [4.7/4.8 Regression] incorrect code generation from g++ -O

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54498

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |rguenth at gcc dot gnu.org
                   |gnu.org                     |

--- Comment #2 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-09-06 09:58:26 UTC ---
Let me see.  We seem to pick up

<bb 2>:
  REALPART_EXPR <prev_ft._M_value> = 0.0;

when optimizing

 <bb 7>:
   D.25613_38 = ft._M_value;
   __r$_M_value = D.25613_38;
-  D.25615_39 = MEM[(const double &)&prev_ft];
+  D.25615_39 = 0.0;

possibly not realizing that

<bb 3>:
  prev_ft = ft;

clobbers it.