Subject: Re: bug#70246: 30.0.50; Update INSTALL for native compilation

From: Stephen Berman <[email-masked]>
Date: Sun, 07 Apr 2024 13:48:41 +0200

On Sun, 07 Apr 2024 09:08:05 +0300 Eli Zaretskii <[email-masked]> wrote:

>> Date: Sat, 06 Apr 2024 22:53:31 +0200
>> From:  Stephen Berman via "Bug reports for GNU Emacs,
>>  the Swiss army knife of text editors" <[email-masked]>
>>
>> The INSTALL file in the Emacs sources makes no reference to native
>> compilation.  The attached patch is an attempt to fill this gap (but I'm
>> not sure about the default locations of installed natively compiled Lisp
>> files, since I do not install Emacs when I build and do not have a
>> distribution installation of Emacs built with native compilation to
>> check).
>
> Thanks.  This LGTM, except the changes to item 6: there, I would only
> mention the possibility of building out of the source tree.  Whether
> running uninstalled is possible in this case depends where is the
> build tree relative to the source tree, so I'd rather not describe all
> the gory details there because they are too complex to explain (what
> you wrote is inaccurate);

There was a mistake at the end of 6b; what I meant to write is "but the
../lib-src and ../native-lisp directories in the build directory
(because the compiled files in these directories are
machine-dependent)."  If there were any other inaccuracies in what I
wrote, can you please point them out to me (for my own edification)?

>                           I'd just say that running uninstalled is
> fully supported only when Emacs is built in the source tree.

So instead of having 6{a,b,c} as in my patch, are the following
additions to the current version (at the end of the first paragraph of
6) ok?

=======================================================================
, ../native-lisp (if built with support for native compilation).

If you build Emacs in a directory separate from the source directory
("out-of-tree"), run 'make' in the build directory.  Then you can
execute the 'src/emacs' file under that directory "in place".  However,
running Emacs uninstalled is fully supported only when it is built in
the source tree.
=======================================================================

But, again for my own edification, can you elaborate what "fully
supported" means here?  I've been running Emacs uninstalled from a build
directory outside of the source tree for many years, and that statement
suggests my builds are deficient (though perhaps only in unobvious ways
that are not crucial for using Emacs), and if so, I'd like to know how
and why.

>> +'/usr/local/share/emacs/VERSION/native-lisp' holds the natively compiled
>> +		pre-loaded Emacs Lisp files.
>
> This is incorrect: native-lisp is installed under /usr/lib/emacs/VERSION,
> not under /usr/share/emacs/VERSION.

I guess you meant /usr/local/lib/emacs/VERSION for the default location?

The above changes are in the attached patch (which also corrects two
typos in my previous patch in the first paragraph under the heading
"Native compilation of Lisp files").

Steve Berman

diff --git a/INSTALL b/INSTALL
index 2aaa02f37d7..edc7f0699e2 100644
--- a/INSTALL
+++ b/INSTALL
@@ -264,6 +264,25 @@ to force GTK+ to run under Broadway, start Emacs like this:
 The GNUstep build also supports the Wayland window system.  If that is
 what you want, see nextstep/INSTALL.

+* Native compilation of Lisp files
+
+In addition to byte-compiling files of Lisp code, Emacs can also produce
+"native code", which usually runs several times faster than the
+corresponding byte-compiled code.  To build Emacs with this feature,
+your system must have not only GCC (the C compiler) and Binutils (the
+assembler and linker) but also the 'libgccjit' shared library, which is
+part of the GCC distribution.  If these components are available,
+building Emacs will automatically produce natively compiled Lisp code.
+
+By default, Emacs natively compiles only pre-loaded Lisp files during
+the build process; other Lisp files are natively compiled
+"just-in-time", i.e, when they are loaded in the running Emacs.  If you
+want Emacs to natively compile all Lisp files during the build ("ahead
+of time"), use the 'configure' option '--with-native-compilation=aot'.
+If you do not want natively compiled Lisp code even if your system
+satisfies the build requirements, use the 'configure' option
+'--with-native-compilation=no'.
+
 DETAILED BUILDING AND INSTALLATION:

 (This is for a Unix or Unix-like system.  For GNUstep and macOS,
@@ -553,10 +572,17 @@ need to create them if you have nothing to put in them.
 wish to add to various termcap entries.  (This is unlikely to be necessary.)

 6) Run 'make' in the top directory of the Emacs distribution to finish
-building Emacs in the standard way.  The final executable file is
-named 'src/emacs'.  You can execute this file "in place" without
-copying it, if you wish; then it automatically uses the sibling
-directories ../lisp, ../lib-src, ../info.
+building Emacs in the standard way.  The final executable file is named
+'src/emacs'.  You can execute this file "in place" without copying it,
+if you wish; then it automatically uses the sibling directories ../lisp,
+../lib-src, ../info, ../native-lisp (if built with support for native
+compilation).
+
+If you build Emacs in a directory separate from the source directory
+("out-of-tree"), run 'make' in the build directory.  Then you can
+execute the 'src/emacs' file under that directory "in place".  However,
+running Emacs uninstalled is fully supported only when it is built in
+the source tree.

 Or you can "install" the executable and the other files into their
 installed locations, with 'make install'.  By default, Emacs's files
@@ -574,6 +600,11 @@ are installed in the following directories:
 		at the same time; in particular, you don't have to
 		make Emacs unavailable while installing a new version.

+'/usr/local/lib/emacs/VERSION/native-lisp' holds the natively compiled
+		pre-loaded Emacs Lisp files.
+
+'~/.emacs.d/eln-cache/' holds the remaining natively compiled Lisp files.
+
 '/usr/local/share/emacs/VERSION/etc' holds the Emacs tutorial, the DOC
 		file, and other architecture-independent files Emacs
 		might need while running.