[Bug libstdc++/81395] [5/6/7/8 Regression] basic_filebuf::overflow recurses and overflows stack

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81395

--- Comment #6 from Paolo Carlini <paolo.carlini at oracle dot com> ---
The relevant xsgetn code essentially is an optimization, right? Shouldn't be
too difficult to figure out what would happen in the slow, correct case...
What's wrong with a normal uncommitted case, thus _M_reading = false?
Performance? Correctness?