[Bug c++/66099] _Pragma diagnostic 'ignored' in macro with strict-overflow not suppressing warning fully with -Werror

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66099

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-06-03
                 CC|                            |manu at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #2 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
This is because the location of the warning is given at 21:19, which is not
within the range affected by the #pragmas. Whether the warning should be given
at the macro definition point or at the expansion point is a matter of debate
(there are at least two PRs open about this, but I don't remember the numbers).

Differences between C and C++ are spurious and may lead to the pragmas applying
or not:

cc1:
/home/manuel/test2/pr66099.cc:21:3: error: assuming signed overflow does not
occur when assuming that (X + c) < X is always false [-Werror=strict-overflow]
   TESTING(i + 4 < i);
   ^

cc1plus:

/home/manuel/test2/pr66099.cc:21:19: error: assuming signed overflow does not
occur when assuming that (X + c) < X is always false [-Werror=strict-overflow]
   TESTING(i + 4 < i);
                   ^

Someone would need to track the locations in GDB and understand why they
diverge. Unfortunately, this is not something that usual devs will spend time
on given the amount of other things waiting to be fixed. If this is important
to you, I would recommend to try to figure out the reason yourself. Once the
problem is clear, it is far more likely that a GCC dev will produce a patch and
fix it.