http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55792
--- Comment #15 from Richard Biener <rguenth at gcc dot gnu.org> 2013-01-08
10:17:16 UTC ---
(In reply to comment #11)
> (In reply to comment #9)
> > Eh. Diego, how does GTY((user)) work here? It smells like a bug in vec.h
> > to me.
> >
> > /* Garbage collection support for vec<T, A, vl_embed>. */
> >
> > template<typename T>
> > void
> > gt_ggc_mx (vec<T, va_gc> *v)
> > {
> > extern void gt_ggc_mx (T &);
> > for (unsigned i = 0; i < v->length (); i++)
> > gt_ggc_mx ((*v)[i]);
> > }
> >
> > doesn't it need to mark the vec itself? Maybe automatic registration of
> > roots (this is a GC root) does not work with GTY((user))?
>
> No. The root is/should be marked by the code calling gt_ggc_mx. gengtype
> will
> generate code like:
>
> if (ggc_test_and_set_mark (x))
> {
> gt_ggc_mx (x);
> }
>
> ggc_test_and_set_mark() is the one that marks the root. Has gengtype
> generated
> a function for this global? It should be something like this
>
> void
> gt_ggc_mx_vec_<mangled_type_name> (void *x_p)
> {
> vec<type_name,va_gc> * const x = (vec<type_name,va_gc> *)x_p;
> if (ggc_test_and_set_mark (x))
> {
> gt_ggc_mx (x);
> }
> }
There is
EXPORTED_CONST struct ggc_root_tab gt_ggc_r_gtype_desc_c[] = {
...
{
<o_global_var_decls,
1,
sizeof (lto_global_var_decls),
>_ggc_mx_vec_tree_va_gc_,
>_pch_nx_vec_tree_va_gc_
},
in gtype-desc.c, which looks like
void
gt_ggc_mx_vec_tree_va_gc_ (void *x_p)
{
vec<tree,va_gc> * const x = (vec<tree,va_gc> *)x_p;
if (ggc_test_and_set_mark (x))
{
gt_ggc_mx (x);
}
}
with
/* If EXPR is not NULL and previously unmarked, mark it and evaluate
to true. Otherwise evaluate to false. */
#define ggc_test_and_set_mark(EXPR) \
((EXPR) != NULL && ((void *) (EXPR)) != (void *) 1 && ! ggc_set_mark (EXPR))
this indeed looks correct to me given vec.h's
template<typename T>
void
gt_ggc_mx (vec<T, va_gc> *v)
{
extern void gt_ggc_mx (T &);
for (unsigned i = 0; i < v->length (); i++)
gt_ggc_mx ((*v)[i]);
}
and the generated(?)
void
gt_ggc_mx (union tree_node *& x)
{
if (x)
gt_ggc_mx_lang_tree_node ((void *) x);
}
So I'm still not sure what HJ means with "it's collected". GC roots are
never collected. HJ, should your patch fix anything? What do you think
the bug is?
