On Tue, May 29, 2018 at 10:16:49AM -0400, Jason Merrill wrote:
> On Tue, May 29, 2018, 4:31 AM Jakub Jelinek <ja...@redhat.com> wrote:
> > Initializing the decomposition temporary from an expression with array type
> > is a special aggregate initialization path in which we wouldn't mark the
> > expression as read for the purposes of -Wunused-but-set*.
> >
> > Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok for
> > trunk?
> >
> > 2018-05-29 Jakub Jelinek <ja...@redhat.com>
> >
> > PR c++/85952
> > * init.c (build_aggr_init): For structured binding initialized from
> > array call mark_rvalue_use on the initializer.
> >
> > * g++.dg/warn/Wunused-var-33.C: New test.
> >
> > --- gcc/cp/init.c.jj 2018-05-25 14:34:41.000000000 +0200
> > +++ gcc/cp/init.c 2018-05-28 19:04:10.504063972 +0200
> > @@ -1678,6 +1678,7 @@ build_aggr_init (tree exp, tree init, in
> > if (VAR_P (exp) && DECL_DECOMPOSITION_P (exp))
> > {
> > from_array = 1;
> > + init = mark_rvalue_use (init);
>
> This should be mark_lvalue_use, since the structured bindings refer to
> the elements of the array rather than copying them. OK with that
> change.
I think they refer to the elements of the decomposition variable (i.e. exp).
"If the assignment-expression in the initializer has array type A and no
ref-qualifier is present, e has type cv A and each element is copy-initialized
or direct-initialized from the
corresponding element of the assignment-expression as specified by the form of
the
initializer."
is what applies in this case, and
int a[2] = {1, 2};
int D.2131[2] = a;
int x [value-expr: D.2131[0]];
int y [value-expr: D.2131[1]];
<<cleanup_point int a[2] = {1, 2};>>;
int D.2131[2] = a;
return <retval> = x + y;
is what original dump shows as implemented, so I don't see a being used here
as an lvalue, we copy the elements into the temporary and that is all where
it is referenced.
Jakub
