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Re: emacs and guile (Re: ehelp woes, or why I hate a module that I love

From: Ken Raeburn
Subject: Re: emacs and guile (Re: ehelp woes, or why I hate a module that I love so much)
Date: Thu, 18 Jul 2002 16:13:58 -0400
User-agent: Gnus/5.090005 (Oort Gnus v0.05) Emacs/21.1.50 (i686-pc-linux-gnu)

>     (BTW, I've got a patch that adds configures option to turn on
>     ENABLE_CHECKING, or just the use of a union for Lisp_Object.  Should I
>     check it in?
> Could you show us what it looks like?

A patch file is appended with my current configure.in changes.  The
ENABLE_CHECKING and USE_LISP_UNION_TYPE macros are already tested in

The CONFIG_NO_DUMP stuff probably isn't of interest, but when I start
playing with Guile again I don't want to have to assume from the start
that libguile is unexec-safe.  Those changes (and a related one in
src/Makefile.in) are just there so I can test the no-unexec case
separately from the Guile work.

> Use of the union type caused the code to be much slower, with typical
> Unix compilers in the 80s.  GCC might do a better job with it, but I think
> it is an interesting question whether the compiled code for Emacs is as good
> when using the union type as it is when using an integer type.  What have
> you observed?

It is still going to be slightly slower than using integer types
anywhere a word-sized union is passed or returned by reference.  I
wouldn't recommend it as a default, because we want all the speed we
can reasonably get, but it's not that painful to use.

I haven't tried any timing tests, but it would be an interesting
experiment to do with modern compilers on various platforms.

I'm also not using it in the Emacs binary I use daily, but I did have
to check to figure that out.  I'll try switching (it's about time I
update to current-CVS again anyways) and see if it's a problem.

Index: configure.in
RCS file: /cvsroot/emacs/emacs/configure.in,v
retrieving revision 1.300
diff -p -u -r1.300 configure.in
--- configure.in        21 Jun 2002 20:57:54 -0000      1.300
+++ configure.in        18 Jul 2002 19:01:15 -0000
@@ -132,6 +132,24 @@ AC_ARG_WITH(xim,
 [  --without-carbon        don't use Carbon GUI on Mac OS X])
+[  --enable-checking       turn on expensive internal run-time consistency
+                             checks (not recommended unless debugging Emacs)])
+if test "${enable_checking}" = yes ; then
+[  --with-union-type       use union type for lisp object representation
+                             (slows performance, better compile-time checks)])
+if test "${with_union_type}" = yes ; then
+[  --disable-unexec        don't generate "dumped" Emacs with pre-loaded lisp])
+if test "${enable_unexec}" = no ; then
 #### Make srcdir absolute, if it isn't already.  It's important to
 #### avoid running the path through pwd unnecessarily, since pwd can
 #### give you automounter prefixes, which can go away.  We do all this
Index: src/config.in
RCS file: /cvsroot/emacs/emacs/src/config.in,v
retrieving revision 1.174
diff -p -u -r1.174 config.in
--- src/config.in       1 May 2002 04:30:59 -0000       1.174
+++ src/config.in       18 Jul 2002 19:01:17 -0000
@@ -916,6 +916,12 @@ extern char *getenv ();
 #define HAVE_X11R6_XIM
+/* Force use of union type for Lisp_Object?  */
+/* Disable unexec code?  */
 /* Should we enable expensive run-time checking of data types?  */

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