alloca: port to compilers that can optimize like GCC 4.6.0

* lib/alloca.c (find_stack_direction): New signature, taken from
Autoconf git.  This works with GCC 4.6.0.  This code should never
be used with GCC 4.6.0 itself, as GCC has alloca, but it might
be used with other compilers that optimize as well as GCC 4.6.0 does.
(alloca): Adjust to new signature.
* m4/alloca.m4 (__AC_LIBOBJ_ALLOCA) [Autoconf version < 2.69]:
New macro, which patches Autoconf in a similar way.

1 files changed, 78 insertions, 1 deletions

diff --git a/m4/alloca.m4 b/m4/alloca.m4
index 689da75a2a..891fc8bc36 100644
--- a/m4/alloca.m4
+++ b/m4/alloca.m4
@@ -1,4 +1,4 @@
-# alloca.m4 serial 11
+# alloca.m4 serial 12
 dnl Copyright (C) 2002-2004, 2006-2007, 2009-2011 Free Software Foundation,
 dnl Inc.
 dnl This file is free software; the Free Software Foundation
@@ -42,3 +42,80 @@ AC_DEFUN([gl_FUNC_ALLOCA],
 # Prerequisites of lib/alloca.c.
 # STACK_DIRECTION is already handled by AC_FUNC_ALLOCA.
 AC_DEFUN([gl_PREREQ_ALLOCA], [:])
+
+# This works around a bug in autoconf <= 2.68.
+# See <http://lists.gnu.org/archive/html/bug-gnulib/2011-06/msg00277.html>.
+
+m4_version_prereq([2.69], [] ,[
+
+# This is taken from the following Autoconf patch:
+# http://git.savannah.gnu.org/cgit/autoconf.git/commit/?id=6cd9f12520b0d6f76d3230d7565feba1ecf29497
+
+# _AC_LIBOBJ_ALLOCA
+# -----------------
+# Set up the LIBOBJ replacement of `alloca'.  Well, not exactly
+# AC_LIBOBJ since we actually set the output variable `ALLOCA'.
+# Nevertheless, for Automake, AC_LIBSOURCES it.
+m4_define([_AC_LIBOBJ_ALLOCA],
+[# The SVR3 libPW and SVR4 libucb both contain incompatible functions
+# that cause trouble.  Some versions do not even contain alloca or
+# contain a buggy version.  If you still want to use their alloca,
+# use ar to extract alloca.o from them instead of compiling alloca.c.
+AC_LIBSOURCES(alloca.c)
+AC_SUBST([ALLOCA], [\${LIBOBJDIR}alloca.$ac_objext])dnl
+AC_DEFINE(C_ALLOCA, 1, [Define to 1 if using `alloca.c'.])
+
+AC_CACHE_CHECK(whether `alloca.c' needs Cray hooks, ac_cv_os_cray,
+[AC_EGREP_CPP(webecray,
+[#if defined CRAY && ! defined CRAY2
+webecray
+#else
+wenotbecray
+#endif
+], ac_cv_os_cray=yes, ac_cv_os_cray=no)])
+if test $ac_cv_os_cray = yes; then
+  for ac_func in _getb67 GETB67 getb67; do
+    AC_CHECK_FUNC($ac_func,
+		  [AC_DEFINE_UNQUOTED(CRAY_STACKSEG_END, $ac_func,
+				      [Define to one of `_getb67', `GETB67',
+				       `getb67' for Cray-2 and Cray-YMP
+				       systems. This function is required for
+				       `alloca.c' support on those systems.])
+    break])
+  done
+fi
+
+AC_CACHE_CHECK([stack direction for C alloca],
+	       [ac_cv_c_stack_direction],
+[AC_RUN_IFELSE([AC_LANG_SOURCE(
+[AC_INCLUDES_DEFAULT
+int
+find_stack_direction (int *addr, int depth)
+{
+  int dir, dummy = 0;
+  if (! addr)
+    addr = &dummy;
+  *addr = addr < &dummy ? 1 : addr == &dummy ? 0 : -1;
+  dir = depth ? find_stack_direction (addr, depth - 1) : 0;
+  return dir + dummy;
+}
+
+int
+main (int argc, char **argv)
+{
+  return find_stack_direction (0, argc + !argv + 20) < 0;
+}])],
+	       [ac_cv_c_stack_direction=1],
+	       [ac_cv_c_stack_direction=-1],
+	       [ac_cv_c_stack_direction=0])])
+AH_VERBATIM([STACK_DIRECTION],
+[/* If using the C implementation of alloca, define if you know the
+   direction of stack growth for your system; otherwise it will be
+   automatically deduced at runtime.
+	STACK_DIRECTION > 0 => grows toward higher addresses
+	STACK_DIRECTION < 0 => grows toward lower addresses
+	STACK_DIRECTION = 0 => direction of growth unknown */
+@%:@undef STACK_DIRECTION])dnl
+AC_DEFINE_UNQUOTED(STACK_DIRECTION, $ac_cv_c_stack_direction)
+])# _AC_LIBOBJ_ALLOCA
+])