util/set: don't compare against deleted entries

When we delete entries in the hash set, we mark them "deleted" by
setting their key to the deleted_key, which points to a dummy
deleted_key_value. When searching for an entry, we normally skip over
those, but set_add() had some code for searching for duplicate entries
which forgot to skip over deleted entries. This led to a segfault inside
the NIR vectorization pass, since its key comparison function
interpreted the memory where deleted_key_value resides as a pointer and
tried to dereference it.

v2:
- add better commit message (Timothy)
- use entry_is_deleted (Timothy)

Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>
Signed-off-by: Connor Abbott <cwabbott0@gmail.com>

src/util/set.c

@@ -282,7 +282,8 @@ set_add(struct set *ht, uint32_t hash, const void *key)
        * If freeing of old keys is required to avoid memory leaks,
        * perform a search before inserting.
        */
-      if (entry->hash == hash &&
+      if (!entry_is_deleted(entry) &&
+          entry->hash == hash &&
           ht->key_equals_function(key, entry->key)) {
          entry->key = key;
          return entry;