https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102697

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[Diagnostics] overflow      |[12 Regression] overflow
                   |warning missing after O2    |warning missing after -O2
                   |vectorization.              |vectorization
   Last reconfirmed|                            |2021-10-12
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
Confirmed as a false negative and a GCC 12 regression.

The expected warning is based on the assumption that an unknown offset to a
subobject is non-negative.  This assumption is supported by the constraint that
pointer arithmetic must be confined to the [sub]object the pointer points to. 
I.e., it's not valid to form a pointer to one subobject by adding an offset to
a pointer to another [sub]object (even within the same object).  The same
constraint is enforced by -Warray-bounds.  The missing -Wstringop-overflow is
due to the hack mentioned in the following discussion:
  https://gcc.gnu.org/pipermail/gcc-patches/2021-September/580172.html

The warning is issued from the strlen pass which runs at -O2 and above.  It's
still issued when -fno-tree-vectorized is specified but should be issued even
with vectorization, and ideally at all optimization levels, including -O0.

Reply via email to