[Bug c++/111090] New: Bogus -Wuninitialized for trivial copy of nested struct with partially initialized array

[Bug c++/111090] New: Bogus -Wuninitialized for trivial copy of nested struct with partially initialized array

[ed at catmur dot uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111090

            Bug ID: 111090
           Summary: Bogus -Wuninitialized for trivial copy of nested
                    struct with partially initialized array
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ed at catmur dot uk
  Target Milestone: ---

struct A {
    A() { buf[0] = 0; }
    int buf[2];
};
struct B { A a; };
struct C {
    C(B const& b) : b(b) {}
    B b;
};
struct D {
    D(C c) : c(c) {}
    C c;
};
D f() { return D(C(B())); }

In constructor 'C::C(const B&)',
    inlined from 'D f()' at <source>:14:16:
<source>:7:21: warning: '<unnamed>.B::a.A::a[1]' is used uninitialized
[-Wuninitialized]
    7 |     C(B const& b) : b(b) {}
      |                     ^~~~
<source>: In function 'D f()':
<source>:14:22: note: '<anonymous>' declared here
   14 | D f() { return D(C(B())); }
      |                      ^

This appears to have started in 7.1.

[Bug c++/111090] Bogus -Wuninitialized for trivial copy of nested struct with partially initialized array

[ed at catmur dot uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111090

--- Comment #1 from Ed Catmur <ed at catmur dot uk> ---
uh, -O -Wall is necessary, obviously. https://godbolt.org/z/eT9dY467P

[Bug tree-optimization/111090] Bogus -Wuninitialized for trivial copy of nested struct with partially initialized array

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111090

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I don't see how it is bogus as you admit it was only partially initialized
even.  The act of copying is still an use IIRC.

[Bug tree-optimization/111090] Bogus -Wuninitialized for trivial copy of nested struct with partially initialized array

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111090

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced to make it obvious what is going on:
```
struct A {
    A() { buf[0] = 0; }
    int buf[2];
};
A g()
{
        A a;
        A b = a;
        return b;
}
```

[Bug tree-optimization/111090] Bogus -Wuninitialized for trivial copy of nested struct with partially initialized array

[ed at catmur dot uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111090

Ed Catmur <ed at catmur dot uk> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #4 from Ed Catmur <ed at catmur dot uk> ---
(In reply to Andrew Pinski from comment #2)
> I don't see how it is bogus as you admit it was only partially initialized
> even.  The act of copying is still an use IIRC.

Sorry, my bad. I reduced it past the point of usefulness and got myself
confused. Thanks.