Re: Redundant if clause in xdisp.c?

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Date: Sat, 29 Aug 2009 17:21:42 -0400
> Cc: emacs-devel@gnu.org
> 
> >> These optimizations seem to be pointless nowadays: even when running
> >> Emacs-23 on my cell-phone (FreeRunner) displaying on my desktop, they
> >> don't make any noticeable difference.
> 
> > How did you turn them off to measure their influence,
> 
> I removed the corresponding code.

I think it's enough to set direction-reversed non-nil.

> > and with what kind of stuff in your buffer(s)?
> 
> I tried it in *scratch* and in a Python-mode buffer (visiting
> /usr/bin/zhone), doing random movement and typing (especially using the
> auto-repeat to see when the redisplay keeps up and when it doesn't).

GUI session or tty?  The price of disabling these optimizations might
be more visible on a tty via a relatively slow link.  I don't think we
should remove them before we try at least that.

> Sure, I just wanted to make sure you don't waste time in these parts of
> the code.

The first rule of optimization: don't do it.  The second rule of
optimization: don't do it yet.  I'm somewhere before the first and the
second one: I need to get the code work right before I make it faster
(if needed).