/* Ensure that p has a back_edges structure associated with it. */
static void ensure_struct(ptr_t p)
{
ptr_t old_back_ptr = GET_OH_BG_PTR(p);
if (!((word)old_back_ptr & FLAG_MANY)) {
back_edges *be = new_back_edges();
be -> flags = 0;
if (0 == old_back_ptr) {
be -> n_edges = 0;
} else {
be -> n_edges = 1;
be -> edges[0] = old_back_ptr;
}
be -> height = HEIGHT_UNKNOWN;
be -> height_gc_no = (unsigned short)(GC_gc_no - 1);
GC_ASSERT(be >= back_edge_space);
SET_OH_BG_PTR(p, (word)be | FLAG_MANY);
}
}
/* q are pointers to the object base, i.e. pointers to an oh. */
static void add_edge(ptr_t p, ptr_t q)
{
ptr_t pred = GET_OH_BG_PTR(q);
back_edges * be, *be_cont;
word i;
GC_ASSERT(p == GC_base(p) && q == GC_base(q));
if (!GC_HAS_DEBUG_INFO(q) || !GC_HAS_DEBUG_INFO(p)) {
/* This is really a misinterpreted free list link, since we saw */
/* a pointer to a free list. Don't overwrite it! */
return;
}
if (NULL == pred) {
static unsigned random_number = 13;
# define GOT_LUCKY_NUMBER (((++random_number) & 0x7f) == 0)
/* A not very random number we use to occasionally allocate a */
/* back_edges structure even for a single backward edge. This */
/* prevents us from repeatedly tracing back through very long */
/* chains, since we will have some place to store height and */
/* in_progress flags along the way. */
SET_OH_BG_PTR(q, p);
if (GOT_LUCKY_NUMBER) ensure_struct(q);
return;
}
/* Check whether it was already in the list of predecessors. */
{
back_edges *e = (back_edges *)((word)pred & ~FLAG_MANY);
word n_edges;
word total;
int local = 0;
if (((word)pred & FLAG_MANY) != 0) {
n_edges = e -> n_edges;
} else if (pred != NULL && ((word)pred & 1) == 0) {
/* A misinterpreted freelist link. */
n_edges = 1;
local = -1;
} else {
n_edges = 0;
}
for (total = 0; total < n_edges; ++total) {
if (local == MAX_IN) {
e = e -> cont;
local = 0;
}
if (local >= 0)
pred = e -> edges[local++];
if (pred == p)
return;
}
}
ensure_struct(q);
be = (back_edges *)((word)GET_OH_BG_PTR(q) & ~FLAG_MANY);
for (i = be -> n_edges, be_cont = be; i > MAX_IN; i -= MAX_IN)
be_cont = be_cont -> cont;
if (i == MAX_IN) {
be_cont -> cont = new_back_edges();
be_cont = be_cont -> cont;
i = 0;
}
be_cont -> edges[i] = p;
be -> n_edges++;
# ifdef DEBUG_PRINT_BIG_N_EDGES
if (GC_print_stats == VERBOSE && be -> n_edges == 100) {
GC_err_printf("The following object has big in-degree:\n");
GC_print_heap_obj(q);
}
# endif
}
