See also L</"Extend PerlIO and PerlIO::Scalar">.
-=head2 Investigate PADTMP hash pessimisation
-
-The peephole optimiser converts constants used for hash key lookups to shared
-hash key scalars. Under ithreads, something is undoing this work.
-See
-L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-09/msg00793.html>
-
=head2 Store the current pad in the OP slab allocator
=for clarification