Re: please review new branch feature/byte-unwind-protect

[Tom Tromey <tom@tromey.com>]

>>>>> "John" == John Wiegley <johnw@gnu.org> writes:

>>>>> "TT" == Tom Tromey <tom@tromey.com> writes:
TT> I recently wrote a couple of patches to add two new bytecodes to Emacs.
TT> These make it possible to compile unwind-protect without the need to
TT> introduce a closure for the unwind forms.

John> Hi Tom,

John> Thanks for these changes. I just want to ask: what motivates them?  Is it
John> efficiency? Does it enable something you can't achieve otherwise? If the
John> former, has it been measured? What is the corresponding cost of having this
John> change?

It's partly for efficiency -- I didn't benchmark it though.  I suppose I
can.  It's pretty normal to see unwind-protect in the expansion of
macros, though; there are plenty in subr.el.  This enables better code
generation in the jit I've written (I plan to post about that when it's
ready but I can do it sooner if you want).

Also this seems like an un-finished to-do item from the lexical binding
conversion.

I don't think there's a cost to this change.  It uses two byte codes,
but there are still some to spare, so I think it isn't a big deal.

Tom