[Bug c++/35652] Location information incorrect on string bounds warning

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

------- Comment #1 from rguenth at gcc dot gnu dot org  2008-03-21 12:49 -------
The warning happens when for example constant propagation tries to optimize
the read from the constant string and calls builtins.c:c_strlen which
produces this warning.  As that warning doesn't specify any location the
current source location is used which is bogus for a warning from the
middle-end.

What we see in the IL that causes this is:

<bb 4>:
  D.12603_7 = append (&s, &"y"[120]);

which is because 'x' + "y" is the same as "y"['x'].

We should avoid re-constructing these out-of-bounds array accesses.

Note that the warning appears multiple times since &"y"[120] is a constant
that is replicated all over the IL and thus present multiple times.
If c_strlen would just return 0 in these cases after warning once that
would fix the issue as well (and it can validly do so, as the code invokes
undefined behavior).


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |diagnostic, wrong-code
      Known to fail|                            |4.3.0
   Last reconfirmed|0000-00-00 00:00:00         |2008-03-21 12:49:51
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35652