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From: "msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/97840] [11 regression] Bogus -Wmaybe-uninitialized
Date: Mon, 16 Nov 2020 01:22:40 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97840

--- Comment #5 from Martin Sebor <msebor at gcc dot gnu.org> ---
The warning code considers more that just TYPE_EMPTY_P():

  /* Avoid warning about empty types such as structs with no members.
     The first_field() test is important for C++ where the predicate
     alone isn't always sufficient.  */
  tree rhstype =3D TREE_TYPE (rhs);
  if (POINTER_TYPE_P (rhstype))
    rhstype =3D TREE_TYPE (rhstype);
  if (TYPE_EMPTY_P (rhstype)
      || (RECORD_OR_UNION_TYPE_P (rhstype)
          && (!first_field (rhstype)
              || default_is_empty_record (rhstype))))
    return NULL_TREE;

If the struct has no data members the warning shouldn't trigger even if
TYPE_EMPTY_P() is false.  I don't think std::allocator has data members so =
we
need to see why the check isn't good enough.  Ah, it looks like the whole
condition is false because default_is_empty_record (rhstype) is false, whic=
h is
because TREE_ADDRESSABLE (rhstype) is true.  Is that what has changed with =
your
patch?  Either way, I do agree that the warning shouldn't be sensitve to ABI
nuances so perhaps default_is_empty_type() (rhstype) would be a better API =
to
use here (except it's static).  Let me look into that.=