Mark bytes undefined in uninit intrinsic.

src/interpreter.rs

@@ -439,8 +439,9 @@ impl<'a, 'tcx: 'a, 'arena> Interpreter<'a, 'tcx, 'arena> {
                 try!(self.memory.copy(src, dest, dest_size));
             }
 
-            // TODO(tsion): Mark bytes as undef.
-            "uninit" => {}
+            "uninit" => {
+                try!(self.memory.mark_definedness(dest, dest_size, false));
+            }
 
             name => panic!("can't handle intrinsic: {}", name),
         }

src/memory.rs

@@ -348,7 +348,9 @@ impl Memory {
         Ok(())
     }
 
-    fn mark_definedness(&mut self, ptr: Pointer, size: usize, new_state: bool) -> EvalResult<()> {
+    pub fn mark_definedness(&mut self, ptr: Pointer, size: usize, new_state: bool)
+        -> EvalResult<()>
+    {
         let mut alloc = try!(self.get_mut(ptr.alloc_id));
         alloc.mark_definedness(ptr.offset, ptr.offset + size, new_state);
         Ok(())