[Bug fortran/31119] -fbounds-check: Check for presence of optional arguments before bound checking

[Joost.VandeVondele at mat dot ethz.ch]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31119

--- Comment #8 from Joost VandeVondele <Joost.VandeVondele at mat dot ethz.ch> 2012-10-20 14:59:08 UTC ---
(In reply to comment #7)
> Hi,
> can someone fortran aware please double-check that the tests
> 
>     * gfortran.dg/bounds_check_9.f90: New test.
>     * gfortran.dg/bounds_check_fail_2.f90: New test.
> 
> do not contain out of bounds access?  I am working on path to bound number of
> loop iterations better based on array accesses and what I see is array A.9
> containing values {1,2} that is accessed in the loop header.
> We bound number of iterations of that loop to 1 (that is one loopback edge
> iteration to walk both parts of the array) and then the testcases start
> failing.
> 
> I do not understand the testcase.
> Perhaps the bounds-check instrumentation happens too late or we need to disable
> this logic with -fbounds-check?
> 
> Honza

According to me, the first testcase (bounds_check_9.f90) should contain no
out-of-bounds access (at least from the fortran point of view, and also
according to valgrind), while the second testcase (bounds_check_fail_2.f90)
does contain out-of-bounds access (by design). Of course, -fbounds-check is
designed to catch out-of-bounds at runtime (which the second testcase tests).
Of course, fortran programs with out-of-bounds access are not standard
conforming. 

Actually, the situation is a bit bizarre. There are no conforming programs for
which bounds-checking can trigger... all these bounds-checking statements can
be just optimized away :-). That's not quite what the users want... I run
-fbounds-check -O2 quite often. I don't think one should switch off
optimization in the presence of -fbounds-check. Maybe the docs should be
enhanced and mention that bounds checking is most effective at -O0 ?