[Bug tree-optimization/104017] unexpeted -Warray-bounds popping a fixed number of std::deque elements

[larsbj at gullik dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104017

Lars Gullik Bjønnes <larsbj at gullik dot net> changed:

           What    |Removed                     |Added
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                 CC|                            |larsbj at gullik dot net

--- Comment #2 from Lars Gullik Bjønnes <larsbj at gullik dot net> ---
(In reply to Martin Sebor from comment #1)

...
> #include <deque>
> 
> struct Node { Node const * parent = nullptr; };
> 
> void func(Node const * n)
> {
>     std::deque<Node const *> p;
> 
>     Node const * e = n;
> 
>     while (e != nullptr) {
>         p.push_front(e);
>         e = e->parent;
>     }
> 
>     if (p.size ())
>       p.pop_front();
>     if (p.size ())
>       p.pop_front();
>     if (p.size ())
>       p.pop_back();
> }
> 
> 
> This test case also triggers a warning, for the same reason: GCC can't
> determine the relationship between a deque's internal node pointers and the
> result of std::deque::size() (which is a function of the node pointers).

This is also the case amended with a check that the std::deque::size is large
enough (for the same reason). In that case the crash can never happen, still
GCC12 warns/errors.

I agree that the first test case, and the warning from it, is helpful. However
this second one not so much.