[Bug tree-optimization/84051] [7/8/9 Regression] missing -Warray-bounds on an out-of-bounds access via an array pointer

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84051

--- Comment #4 from Martin Sebor <msebor at gcc dot gnu.org> ---
I see GCC warns for this case with -Warray-bounds=2 and it's being tested in
gcc.dg/Warray-bounds-11.c.

I think it would make sense to warn on the pointer to array case even at level
1.  It seems quite unlikely for a pointer to an array of a known bound to be
set to point to a larger array and used to access elements beyond that bound.

Separately, I also wonder if it would make sense to warn for out-of-bounds
accesses to trailing arrays with more than 1 element.  Those too seem unlikely,
and the recommendation is to use either flexible array members or zero-length
arrays for such things.

By warning on these cases GCC would help detect more bugs and encourage working
code to migrate to the recommended solutions.

Perhaps for GCC 10.