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

From: Tom Tromey
Subject: Re: please review new branch feature/byte-unwind-protect
Date: Tue, 23 Jan 2018 08:50:33 -0700
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.0.91 (gnu/linux)

>>>>> "John" == John Wiegley <address@hidden> writes:

>>>>> "TT" == Tom Tromey <address@hidden> 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 
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

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.


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