'tmp' directory is too big in iOS

I made an app which is 40 MB (very big for me).

But the real surprise is that I found the tmp directory is 300 MB!

And I haven't saved any files in the document yet!

All the files' names in tmp are like:

stack-logs.80127.MyAppName.index
stack-logs.80163.MyAppName.vwnxgi.link
...

What are these things? They occupied an unbelievably 300 MB size!

Is there a way I can clear them periodically? Or is this because I'm debugging my app on my iPhone?