--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2008-11-20  Bruno Haible  <bruno@clisp.org>
+
+	Attempt to work around an AIX 5.3, 6.1 compiler bug with include_next.
+	* lib/math.in.h: Use INCLUDE_NEXT_AS_FIRST_DIRECTIVE instead of
+	INCLUDE_NEXT.
+	* m4/include_next.m4 (gl_INCLUDE_NEXT): Set also
+	INCLUDE_NEXT_AS_FIRST_DIRECTIVE.
+	* modules/math (Makefile.am): Substitute
+	INCLUDE_NEXT_AS_FIRST_DIRECTIVE instead of INCLUDE_NEXT.
+
 2008-11-18  Alexandre Duret-Lutz  <adl@lrde.epita.fr>
             Bruno Haible  <bruno@clisp.org>
 

--- a/lib/math.in.h
+++ b/lib/math.in.h
@@ -22,7 +22,7 @@
 #endif
 
 /* The include_next requires a split double-inclusion guard.  */
-#@INCLUDE_NEXT@ @NEXT_MATH_H@
+#@INCLUDE_NEXT_AS_FIRST_DIRECTIVE@ @NEXT_MATH_H@
 
 #ifndef _GL_MATH_H
 #define _GL_MATH_H

--- a/m4/include_next.m4
+++ b/m4/include_next.m4
@@ -1,4 +1,4 @@
-# include_next.m4 serial 9
+# include_next.m4 serial 10
 dnl Copyright (C) 2006-2008 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -11,6 +11,10 @@
 dnl INCLUDE_NEXT expands to 'include_next' if the compiler supports it, or to
 dnl 'include' otherwise.
 dnl
+dnl INCLUDE_NEXT_AS_FIRST_DIRECTIVE expands to 'include_next' if the compiler
+dnl supports it in the special case that it is the first include directive in
+dnl the given file, or to 'include' otherwise.
+dnl
 dnl PRAGMA_SYSTEM_HEADER can be used in files that contain #include_next,
 dnl so as to avoid GCC warnings when the gcc option -pedantic is used.
 dnl '#pragma GCC system_header' has the same effect as if the file was found
@@ -26,12 +30,26 @@
   AC_LANG_PREPROC_REQUIRE()
   AC_CACHE_CHECK([whether the preprocessor supports include_next],
     [gl_cv_have_include_next],
-    [rm -rf conftestd1 conftestd2
-     mkdir conftestd1 conftestd2
+    [rm -rf conftestd1a conftestd1b conftestd2
+     mkdir conftestd1a conftestd1b conftestd2
      dnl The include of <stdio.h> is because IBM C 9.0 on AIX 6.1 supports
      dnl include_next when used as first preprocessor directive in a file,
-     dnl but not when preceded by another include directive.
-     cat <<EOF > conftestd1/conftest.h
+     dnl but not when preceded by another include directive. Additionally,
+     dnl with this same compiler, include_next is a no-op when used in a
+     dnl header file that was included by specifying its absolute file name.
+     dnl Despite these two bugs, include_next is used in the compiler's
+     dnl <math.h>. By virtue of the second bug, we need to use include_next
+     dnl as well in this case.
+     cat <<EOF > conftestd1a/conftest.h
+#define DEFINED_IN_CONFTESTD1
+#include_next <conftest.h>
+#ifdef DEFINED_IN_CONFTESTD2
+int foo;
+#else
+#error "include_next doesn't work"
+#endif
+EOF
+     cat <<EOF > conftestd1b/conftest.h
 #define DEFINED_IN_CONFTESTD1
 #include <stdio.h>
 #include_next <conftest.h>
@@ -47,24 +65,36 @@
 #endif
 #define DEFINED_IN_CONFTESTD2
 EOF
-     save_CPPFLAGS="$CPPFLAGS"
-     CPPFLAGS="$CPPFLAGS -Iconftestd1 -Iconftestd2"
+     gl_save_CPPFLAGS="$CPPFLAGS"
+     CPPFLAGS="$gl_save_CPPFLAGS -Iconftestd1b -Iconftestd2"
      AC_COMPILE_IFELSE([#include <conftest.h>],
        [gl_cv_have_include_next=yes],
-       [gl_cv_have_include_next=no])
-     CPPFLAGS="$save_CPPFLAGS"
-     rm -rf conftestd1 conftestd2
+       [CPPFLAGS="$gl_save_CPPFLAGS -Iconftestd1a -Iconftestd2"
+        AC_COMPILE_IFELSE([#include <conftest.h>],
+          [gl_cv_have_include_next=buggy],
+          [gl_cv_have_include_next=no])
+       ])
+     CPPFLAGS="$gl_save_CPPFLAGS"
+     rm -rf conftestd1a conftestd1b conftestd2
     ])
   PRAGMA_SYSTEM_HEADER=
   if test $gl_cv_have_include_next = yes; then
     INCLUDE_NEXT=include_next
+    INCLUDE_NEXT_AS_FIRST_DIRECTIVE=include_next
     if test -n "$GCC"; then
       PRAGMA_SYSTEM_HEADER='#pragma GCC system_header'
     fi
   else
-    INCLUDE_NEXT=include
+    if test $gl_cv_have_include_next = buggy; then
+      INCLUDE_NEXT=include
+      INCLUDE_NEXT_AS_FIRST_DIRECTIVE=include_next
+    else
+      INCLUDE_NEXT=include
+      INCLUDE_NEXT_AS_FIRST_DIRECTIVE=include
+    fi
   fi
   AC_SUBST([INCLUDE_NEXT])
+  AC_SUBST([INCLUDE_NEXT_AS_FIRST_DIRECTIVE])
   AC_SUBST([PRAGMA_SYSTEM_HEADER])
 ])
 

--- a/modules/math
+++ b/modules/math
@@ -20,7 +20,7 @@
 math.h: math.in.h
 	rm -f $@-t $@
 	{ echo '/* DO NOT EDIT! GENERATED AUTOMATICALLY! */' && \
-	  sed -e 's|@''INCLUDE_NEXT''@|$(INCLUDE_NEXT)|g' \
+	  sed -e 's|@''INCLUDE_NEXT_AS_FIRST_DIRECTIVE''@|$(INCLUDE_NEXT_AS_FIRST_DIRECTIVE)|g' \
 	      -e 's|@''PRAGMA_SYSTEM_HEADER''@|@PRAGMA_SYSTEM_HEADER@|g' \
 	      -e 's|@''NEXT_MATH_H''@|$(NEXT_MATH_H)|g' \
 	      -e 's|@''GNULIB_CEILF''@|$(GNULIB_CEILF)|g' \