want to determine what ops I<really> are the most commonly used. And in turn
suggest evictions and promotions to achieve a better F<pp_hot.c>.
-=head2 Shrink struct context
-
-In F<cop.h>, we have
-
- struct context {
- U32 cx_type; /* what kind of context this is */
- union {
- struct block cx_blk;
- struct subst cx_subst;
- } cx_u;
- };
-
-There are less than 256 values for C<cx_type>, and the constituent parts
-C<struct block> and C<struct subst> both contain some C<U8> and C<U16> fields,
-so it should be possible to move them to the first word, and share space with
-a C<U8> C<cx_type>, saving 1 word.
-
=head2 Allocate OPs from arenas
Currently all new OP structures are individually malloc()ed and free()d.