In ceval.c we find

		/* XXX Perhaps we should create a specialized
		   PyFrame_New() that doesn't take locals, but does
		   take builtins without sanity checking them.
		*/

This patch takes that idea rather further than you
might have expected... it creates a "light" subtype of
frame that assumes certain things about the frame,
gives this type its own free list (so it can assume
more about objects on the freelist) and converts light
frames into "heavy" frames when assumptions stop being
true.

Good for a ~5% improvement on "./python -s 'def f():
pass' 'f()'"; a bit less on pystone.  It also conflicts
slightly with my function reorg patch -- apply that
first, apply this, ignore the reject and edit
func_caller_nofrees in funcobject.c to call
PyFrame_NewLight.

All three patches I just submitted together get ~6% on
pystone.