[Bug c++/19808] miss a warning about uninitialized members in constructor

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=19808

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |jason at gcc dot gnu.org

--- Comment #22 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Manuel LÃpez-IbÃÃez from comment #21)
> I just got hit by this bug. This can obviously be warned in the FE as clang
> does:
> 
> test.cc:4:11: warning: field 'j' is uninitialized when used here
> [-Wuninitialized]
>   S() : i(j), j(1) {} 
>           ^
> 
> simply by marking the members somehow as initialized or not, and when using
> them realizing that they are still uninitialized.
> 
> Marek, Paolo, Jason? Any idea how to do this?

It could be done specifically for uses in mem-initializers by walking the
initializer in perform_mem_init to look for any references to members that
haven't been marked yet.

A more general warning that would cover, say,

X x;
x.x = x.y;

would need support in the existing back end -Wuninitialized code.