On 28/01/19 14:29 +0100, Jakub Jelinek wrote:
On Mon, Jan 28, 2019 at 01:55:38PM +0100, Richard Biener wrote:
So I guess in the end we're being lucky. Somehow. I've played with
__attribute__((noipa)) void
qux ()
{
S buf1;
foo ((char *)&buf1);
S *p = new (&buf1) (S);
bar (p);
p->~S ();
{
char buf2[128];
baz (buf2);
}
}
I'd think the above is already invalid, by doing a placement new into
a variable with non-trivial ctor and dtor while it is still constructed,
then destruct the placement new created var in there and after a while
destruct the original variable doesn't feel right to me, but I'm not a C++
Right. When the second object is constructed in that location, the
lifetime of the first one ends. When the destructor is automatically
run at the end of the scope you're destroying something that is no
longer alive, so undefined.
language lawyer. I'd expect that usually either the whole var has
char/std::byte etc. array type, or the placement new is into a field inside
of some class (again char/std::byte etc. array type).
Would could be valid is:
Yeah I think the one below is OK. I'm still looking at the original
testcase at the top of the thread.
__attribute__((noipa)) void
qux ()
{
S buf1;
foo (buf1.buf);
S *p = new (buf1.buf) (S);
bar (p);
p->~S ();
{
char buf2[128];
baz (buf2);
}
}
but we don't really fold that into VAR_DECL lhs either, the type in the
MEM_REF isn't really S even in this case, but CLASSTYPE_AS_BASE of the S
type.
Jakub
