USE_LSB_TAG and Solaris 10

USE_LSB_TAG and Solaris 10

[Paul Eggert]

Stefan suggested that I look into why USE_LSB_TAG wasn't used
with Sun cc, or on Solaris 10.

It turns out that Sun cc now supports __attribute__ ((__aligned__ (E)))
a la GCC.  Also, Solaris 10 malloc (which GCC uses) aligns to 8.
So I installed this performance improvement into the trunk.

=== modified file 'ChangeLog'
--- ChangeLog	2011-01-17 19:20:37 +0000
+++ ChangeLog	2011-01-18 04:54:43 +0000
@@ -1,3 +1,10 @@
+2011-01-18  Paul Eggert  <eggert@cs.ucla.edu>
+
+	* configure.in (HAVE_ATTRIBUTE_ALIGNED): Arrange for this to be
+	defined if the compiler supports GCC-style __attribute__
+	((__aligned__ ...)).  IBM AIX and Oracle Solaris Studio support
+	this syntax.
+
 2011-01-17  Paul Eggert  <eggert@cs.ucla.edu>
 
 	Makefile.in: tidy up the building of lib

=== modified file 'configure.in'
--- configure.in	2011-01-17 19:01:01 +0000
+++ configure.in	2011-01-18 04:54:43 +0000
@@ -1323,6 +1323,19 @@
 dnl Check for endianess
 AC_C_BIGENDIAN
 
+AC_CACHE_CHECK([for  __attribute__ ((__aligned__ (expr)))],
+  [emacs_cv_attribute_aligned],
+  [AC_COMPILE_IFELSE(
+     [AC_LANG_PROGRAM(
+	[[char __attribute__ ((__aligned__ (1 << 3))) c;]],
+	[[]])],
+     [emacs_cv_attribute_aligned=yes],
+     [emacs_cv_attribute_aligned=no])])
+if test $emacs_cv_attribute_aligned = yes; then
+  AC_DEFINE([HAVE_ATTRIBUTE_ALIGNED], 1,
+    [Define to 1 if GCC-style __attribute__ ((__aligned__ (expr))) works.])
+fi
+
 dnl check for Make feature
 AC_PROG_MAKE_SET
 
@@ -3734,4 +3747,3 @@
 fi
 
 ], [GCC="$GCC" NON_GNU_CPP="$NON_GNU_CPP" CPP="$CPP" CPPFLAGS="$CPPFLAGS"])
-

=== modified file 'src/ChangeLog'
--- src/ChangeLog	2011-01-18 02:49:59 +0000
+++ src/ChangeLog	2011-01-18 04:54:43 +0000
@@ -1,3 +1,11 @@
+2011-01-18  Paul Eggert  <eggert@cs.ucla.edu>
+
+	* lisp.h (DECL_ALIGN): Define if HAVE_ATTRIBUTE_ALIGNED, not if
+	defined __GNUC__.  ../configure now checks for this GCC feature,
+	which is now also supported by IBM and Oracle compilers.
+	(USE_LSB_TAG) [defined DECL_ALIGN]: Also define if defined __sun,
+	since Solaris malloc returns mult-of-8.
+
 2011-01-18  Stefan Monnier  <monnier@iro.umontreal.ca>
 
 	* image.c (syms_of_image): Don't access XSYMBOL's internals directly.

=== modified file 'src/lisp.h'
--- src/lisp.h	2011-01-17 19:24:36 +0000
+++ src/lisp.h	2011-01-18 04:54:43 +0000
@@ -122,16 +122,18 @@
    TYPEBITS-aligned. */
 #ifndef NO_DECL_ALIGN
 # ifndef DECL_ALIGN
-/* What compiler directive should we use for non-gcc compilers?  -stef  */
-#  if defined (__GNUC__)
+#  if HAVE_ATTRIBUTE_ALIGNED
 #   define DECL_ALIGN(type, var) \
      type __attribute__ ((__aligned__ (1 << GCTYPEBITS))) var
+#  else
+     /* What directives do other compilers use?  */
 #  endif
 # endif
 #endif
 
 /* Let's USE_LSB_TAG on systems where we know malloc returns mult-of-8.  */
-#if defined GNU_MALLOC || defined DOUG_LEA_MALLOC || defined __GLIBC__ || defined DARWIN_OS
+#if (defined GNU_MALLOC || defined DOUG_LEA_MALLOC || defined __GLIBC__ \
+     || defined DARWIN_OS || defined __sun)
 /* We also need to be able to specify mult-of-8 alignment on static vars.  */
 # if defined DECL_ALIGN
 #  define USE_LSB_TAG

Re: USE_LSB_TAG and Solaris 10

[Eli Zaretskii]

> Date: Mon, 17 Jan 2011 21:04:27 -0800
> From: Paul Eggert <eggert@cs.ucla.edu>
> Cc: Stefan Monnier <monnier@iro.umontreal.ca>
> 
> It turns out that Sun cc now supports __attribute__ ((__aligned__ (E)))
> a la GCC.  Also, Solaris 10 malloc (which GCC uses) aligns to 8.
> So I installed this performance improvement into the trunk.
> 
> === modified file 'ChangeLog'
> --- ChangeLog	2011-01-17 19:20:37 +0000
> +++ ChangeLog	2011-01-18 04:54:43 +0000
> @@ -1,3 +1,10 @@
> +2011-01-18  Paul Eggert  <eggert@cs.ucla.edu>
> +
> +	* configure.in (HAVE_ATTRIBUTE_ALIGNED): Arrange for this to be
> +	defined if the compiler supports GCC-style __attribute__
> +	((__aligned__ ...)).  IBM AIX and Oracle Solaris Studio support
> +	this syntax.

And what do you think this change will do to platforms that don't run
the configure script, but do use GCC?

Re: USE_LSB_TAG and Solaris 10

[Paul Eggert]

On 01/18/11 07:04, Eli Zaretskii wrote:
> And what do you think this change will do to platforms that don't run
> the configure script, but do use GCC?

These platforms should still work; they just won't use the
USE_LSB_TAG optimization.  At some point the maintainers
for these non-Posix platforms should arrange for their
configuration procedure to set HAVE_ATTRIBUTE_ALIGNED
if that is appropriate for optimization on their platforms.

Re: USE_LSB_TAG and Solaris 10

[Eli Zaretskii]

> Date: Tue, 18 Jan 2011 10:25:21 -0800
> From: Paul Eggert <eggert@cs.ucla.edu>
> CC: emacs-devel@gnu.org, monnier@iro.umontreal.ca
> 
> On 01/18/11 07:04, Eli Zaretskii wrote:
> > And what do you think this change will do to platforms that don't run
> > the configure script, but do use GCC?
> 
> These platforms should still work; they just won't use the
> USE_LSB_TAG optimization.  At some point the maintainers
> for these non-Posix platforms should arrange for their
> configuration procedure to set HAVE_ATTRIBUTE_ALIGNED
> if that is appropriate for optimization on their platforms.

Avoiding that needs a simple change in exactly 2 files: nt/config.nt
for the Windows build and msdos/sed2v2.inp for the MS-DOS build.

Re: USE_LSB_TAG and Solaris 10

[Stefan Monnier]

> they just won't use the USE_LSB_TAG optimization.

Just a clarification: USE_LSB_TAG is not an really optimization, or at
least I don't think anyone has tried to measure its performance.  It is
meant to let Emacs use all the available virtual memory rather than be
limited to 128MB (IIRC) of memory on 32bit systems (not to be confused
with the limit on maximum buffer size, which is determined by the
largest fixnum, i.e. 512MB on 32bit systems on the trunk).


        Stefan