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Re: Anyone built Emacs with gcc-3.3?

From: Paul Eggert
Subject: Re: Anyone built Emacs with gcc-3.3?
Date: Sun, 13 Jul 2003 22:52:44 -0700 (PDT)

> From: Simon Leinen <address@hidden>
> Date: Sun, 13 Jul 2003 16:56:09 +0200
> Do you think it would be useful for me to test your patches in other
> compilation modes as well?

I am testing 32-bit Solaris sparc (both Solaris 8 and 9) in everyday
use, so you needn't bother with those cases.  It'd be nice to test it
on older Solaris releases.

However, I discovered that the zero-initializer changes
are not needed on Solaris 8 or 9, since unexelf.c does not attempt to
make any of the initialized data read-only.

On further thought, those changes are not urgent: they are only an
optimization, and they help only on hosts where dumping the 'pure'
array into readonly text is a real performance win.  This used to be a
big deal (15 years ago, say), but I suspect it's not that important
these days.  Certainly small things like scalars are not worth
worrying about now, from a performance viewpoint; only arrays like
'pure' matter.

Since the zero-initializer changes don't fix any real bug that I know
of, I didn't install them into the RC branch.  And I omitted the
proposed changes to scalars, leaving only the following small change
that I just installed into the trunk.

2003-07-13  Paul Eggert  <address@hidden>

        GCC 3.3 (sparc) no longer puts "int foo = 0;" into data; it
        puts it into BSS instead, at least on Solaris 8 and 9.
        This is a valid optimization, and it may occur on other platforms,
        so Emacs should not assume that initializing a static variable to
        zero puts it into data.
        * alloc.c (pure, staticvec):
        Initialize these arrays to nonzero, so that they're not
        put into BSS by that optimization.

Index: alloc.c
RCS file: /cvsroot/emacs/emacs/src/alloc.c,v
retrieving revision 1.314
retrieving revision 1.315
diff -p -u -r1.314 -r1.315
--- alloc.c     14 Jul 2003 02:51:08 -0000      1.314
+++ alloc.c     14 Jul 2003 05:37:52 -0000      1.315
@@ -185,9 +185,10 @@ Lisp_Object Vmemory_full;
 #ifndef HAVE_SHM
-/* Force it into data space! */
+/* Force it into data space!  Initialize it to a nonzero value;
+   otherwise some compilers put it into BSS.  */
-EMACS_INT pure[PURESIZE / sizeof (EMACS_INT)] = {0,};
+EMACS_INT pure[PURESIZE / sizeof (EMACS_INT)] = {1,};
 #define PUREBEG (char *) pure
 #else /* HAVE_SHM */
@@ -404,10 +405,11 @@ static void check_gcpros P_ ((void));
 struct gcpro *gcprolist;
-/* Addresses of staticpro'd variables.  */
+/* Addresses of staticpro'd variables.  Initialize it to a nonzero
+   value; otherwise some compilers put it into BSS.  */
 #define NSTATICS 1280
-Lisp_Object *staticvec[NSTATICS] = {0};
+Lisp_Object *staticvec[NSTATICS] = {&Vpurify_flag};
 /* Index of next unused slot in staticvec.  */

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