optimize iterator construction

Signed-off-by: Jason Volk <[email protected]>

Author: jevolk

src/db_iterator.rs

@@ -107,13 +107,13 @@ impl<'a, D: DBAccess> DBRawIteratorWithThreadMode<'a, D> {
     }
 
     fn from_inner(inner: *mut ffi::rocksdb_iterator_t, readopts: ReadOptions) -> Self {
-        // This unwrap will never fail since rocksdb_create_iterator and
+        // SAFETY: This unwrap will never fail since rocksdb_create_iterator and
         // rocksdb_create_iterator_cf functions always return non-null. They
         // use new and deference the result so any nulls would end up with SIGSEGV
         // there and we would have a bigger issue.
-        let inner = std::ptr::NonNull::new(inner).unwrap();
+        unsafe { std::hint::assert_unchecked(!inner.is_null()) };
         Self {
-            inner,
+            inner: std::ptr::NonNull::new(inner).unwrap(),
             _readopts: readopts,
             db: PhantomData,
         }