util/hash_table: Assert that keys are not reserved pointers

If we insert a NULL key, it will appear to succeed but will mess up
entry counting.  Similar errors can occur if someone accidentally
inserts the deleted key.  The later is highly unlikely but technically
possible so we should guard against it too.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>

src/util/hash_table.c

@@ -98,6 +98,12 @@ static const struct {
    ENTRY(2147483648ul, 2362232233ul, 2362232231ul )
 };
 
+static inline bool
+key_pointer_is_reserved(const struct hash_table *ht, const void *key)
+{
+   return key == NULL || key == ht->deleted_key;
+}
+
 static int
 entry_is_free(const struct hash_entry *entry)
 {
@@ -250,6 +256,8 @@ _mesa_hash_table_set_deleted_key(struct hash_table *ht, const void *deleted_key)
 static struct hash_entry *
 hash_table_search(struct hash_table *ht, uint32_t hash, const void *key)
 {
+   assert(!key_pointer_is_reserved(ht, key));
+
    uint32_t size = ht->size;
    uint32_t start_hash_address = util_fast_urem32(hash, size, ht->size_magic);
    uint32_t double_hash = 1 + util_fast_urem32(hash, ht->rehash,
@@ -366,7 +374,7 @@ hash_table_insert(struct hash_table *ht, uint32_t hash,
 {
    struct hash_entry *available_entry = NULL;
 
-   assert(key != NULL);
+   assert(!key_pointer_is_reserved(ht, key));
 
    if (ht->entries >= ht->max_entries) {
       _mesa_hash_table_rehash(ht, ht->size_index + 1);