On Mon, 4 Feb 2019, Steven Bosscher wrote:
> On Mon, Feb 4, 2019 at 2:16 PM Richard Biener <rguent...@suse.de> wrote:
> > When I introduced tree-form bitmaps I forgot to think about GC.
> > The following drops the chain_prev annotation to make the marker
> > work for trees.
>
> I don't understand this patch. How are the nodes in a bitmap tree now
> to be found for marking?
>
> This patch should cause an ICE on test cases with bitmaps as trees
> with ENABLE_GC_ALWAYS_COLLECT.
After the patch the marker routines look like
void
gt_ggc_mx_bitmap_head (void *x_p)
{
struct bitmap_head * const x = (struct bitmap_head *)x_p;
if (ggc_test_and_set_mark (x))
{
gt_ggc_m_14bitmap_element ((*x).first);
}
}
void
gt_ggc_mx_bitmap_element (void *x_p)
{
struct bitmap_element * x = (struct bitmap_element *)x_p;
struct bitmap_element * xlimit = x;
while (ggc_test_and_set_mark (xlimit))
xlimit = ((*xlimit).next);
while (x != xlimit)
{
gt_ggc_m_14bitmap_element ((*x).next);
gt_ggc_m_14bitmap_element ((*x).prev);
x = ((*x).next);
}
}
gt_ggc_m_14bitmap_element just is a NULL protected call to
gt_ggc_mx_bitmap_element. So bitmap elements are marked
by marking the ->next chain until we hit an already marked
node and then recurse on all prev and next members
(where the recursion will not chain ->next because we've
already marked it).
Previously it was
void
gt_ggc_mx_bitmap_element (void *x_p)
{
struct bitmap_element * x = (struct bitmap_element *)x_p;
struct bitmap_element * xlimit = x;
while (ggc_test_and_set_mark (xlimit))
xlimit = ((*xlimit).next);
if (x != xlimit)
for (;;)
{
struct bitmap_element * const xprev = ((*x).prev);
if (xprev == NULL) break;
x = xprev;
(void) ggc_test_and_set_mark (xprev);
}
while (x != xlimit)
{
gt_ggc_m_14bitmap_element ((*x).next);
gt_ggc_m_14bitmap_element ((*x).prev);
x = ((*x).next);
}
}
where the prev_chain handling "wrecked" things for trees
and didn't help for the list implementation (since we've
only come here via the bitmap_head->first link).
Richard.
