util/set: add macro for destructively iterating set entries

a common usage for sets is for tracking exactly one instance of a pointer
for a given period of time, after which the set's entries are purged and it
is reused

this macro enables the purge phase of such usage to reset the table to a
pristine state, avoiding future rehashing due to ballooning of deleted entries

Reviewed-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8498>

src/util/set.h

@@ -111,6 +111,8 @@ _mesa_set_remove_key(struct set *set, const void *key);
 
 struct set_entry *
 _mesa_set_next_entry(const struct set *set, struct set_entry *entry);
+struct set_entry *
+_mesa_set_next_entry_unsafe(const struct set *set, struct set_entry *entry);
 
 struct set_entry *
 _mesa_set_random_entry(struct set *set,
@@ -132,6 +134,15 @@ _mesa_set_intersects(struct set *a, struct set *b);
         entry != NULL;                                              \
         entry = _mesa_set_next_entry(set, entry))
 
+/**
+ * This foreach function destroys the table as it iterates.
+ * It is not safe to use when inserting or removing entries.
+ */
+#define set_foreach_remove(set, entry)                              \
+   for (struct set_entry *entry = _mesa_set_next_entry_unsafe(set, NULL);  \
+        (set)->entries;                                              \
+        entry->hash = 0, entry->key = (void*)NULL, (set)->entries--, entry = _mesa_set_next_entry_unsafe(set, entry))
+
 #ifdef __cplusplus
 } /* extern C */
 #endif