[Bug c++/61597] Unexpected behavior at runtime

["glisse at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61597

--- Comment #17 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #16)
> Marc:
> 
> struct Iter
> {
>   Iter& operator+=(int) { return *this; }
> 
>   int operator*() { return i; }
> 
>   int i;
> };
> 
> Iter& func(Iter iter, int n) {
>     return iter += n;
> }
> 
> int main()
> {
>     Iter iter = Iter();
>     Iter it = func(iter, 2);
>     return *it;
> }

Thanks, I only need to add to my patch:
 || TREE_CODE (valbase) == PARM_DECL
in find_explicit_erroneous_behaviour and it warns for this at -O2. I was only
handling local variables and not parameters. I'll have to check if returning
the address of a PARM_DECL is always wrong. And if func is inline, it will
require -fkeep-inline-functions.

e.cc: In function 'Iter& func(Iter, int)':
e.cc:11:20: warning: function returns address of local variable
[-Wreturn-local-addr]
     return iter += n;
                    ^
e.cc:10:17: note: declared here
 Iter& func(Iter iter, int n) {
                 ^