Why does GCC say “named return values no longer supported”?

See here – early NRVO implementation by explicit definition of the named return value in the function header.

Native support for NRVO without this extension was added here – GCC 3.1 Release Series.

Brief cut and paste for context:

G++ now supports the “named return
value optimization”: for code like

A f () {
  A a;
  ...
  return a;
}

G++ will allocate a in the return
value slot, so that the return becomes
a no-op. For this to work, all return
statements in the function must return
the same variable.