Re: AC_C_RESTRICT

[Ralf Wildenhues]

Hi Albert,

* Albert Chin wrote on Fri, Mar 31, 2006 at 10:40:14PM CEST:
> On Fri, Mar 31, 2006 at 02:25:51PM -0600, Albert Chin wrote:
> > Autoconf 2.59 chooses __restrict on HP-UX 11.x.

> typedef int * int_ptr;
> 
> void
> foo (int_ptr __restrict rp) {
>   int i;
> }
>   $ cc -c a.c
> cc: "a.c", line 4: error 1671: Illegal use of restrict.
> 
> If I replace the parameter list with "int *" rather than "int_ptr",
> then it works. Compiler bug?

I think so.  Probably a good idea to check this in _AC_PROG_CC_C99 as
well.  While at it, let's remove the `unused variable' warnings so this
works with -Werror.

AC_C_RESTRICT also suffers from the cleanup buglet mentioned a couple of
days ago, as well as AC_C_INLINE.  I noticed furthermore that neither of
these macros is tested by the testsuite.

OK to apply this patch to address all of this?

Cheers,
Ralf

        * lib/autoconf/c.m4 (AC_C_INLINE): Do not skip cleanup code.
        (AC_C_RESTRICT): Likewise.  Furthermore, add a function with a
        typedef'ed restricted pointer, to catch a compiler bug on
        HP-UX 11.x, and fix warnings so it passes with -Werror.
        (_AC_PROG_CC_C99): Likewise.
        Reported by Albert Chin <address@hidden>.
        * tests/mktests.sh: Do not skip AC_C_INLINE, AC_C_RESTRICT.

Index: lib/autoconf/c.m4
===================================================================
RCS file: /cvsroot/autoconf/autoconf/lib/autoconf/c.m4,v
retrieving revision 1.217
diff -u -r1.217 c.m4
--- lib/autoconf/c.m4   3 Apr 2006 03:18:39 -0000       1.217
+++ lib/autoconf/c.m4   3 Apr 2006 16:51:26 -0000
@@ -1092,8 +1092,10 @@
   double average;
 };
 
+typedef const char *ccp;
+
 static inline int
-test_restrict(const char *restrict text)
+test_restrict(ccp restrict text)
 {
   // See if C++-style comments work.
   // Iterate through items via the restricted pointer.
@@ -1169,6 +1171,9 @@
 
   int dynamic_array[ni.number];
   dynamic_array[43] = 543;
+
+  // work around unused variable warnings
+  return  bignum == 0LL || ubignum == 0uLL || newvar[0] == 'x';
 ]],
 dnl Try
 dnl GCC                -std=gnu99 (unused restrictive modes: -std=c99 
-std=iso9899:1999)
@@ -1397,7 +1381,8 @@
 $ac_kw foo_t foo () {return 0; }
 #endif
 ])],
-                   [ac_cv_c_inline=$ac_kw; break])
+                   [ac_cv_c_inline=$ac_kw])
+  test "$ac_cv_c_inline" != no && break
 done
 ])
 AH_VERBATIM([inline],
@@ -1505,9 +1490,17 @@
    # Try the official restrict keyword, then gcc's __restrict, and
    # the less common variants.
    for ac_kw in restrict __restrict __restrict__ _Restrict; do
-     AC_COMPILE_IFELSE([AC_LANG_SOURCE(
-      [float * $ac_kw x;])],
-      [ac_cv_c_restrict=$ac_kw; break])
+     AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
+      [[typedef int * int_ptr;
+        int foo (int_ptr $ac_kw ip) {
+        return ip[0];
+       }]],
+      [[int s[1];
+        int * $ac_kw t = s;
+        t[0] = 0;
+        return foo(t)]])],
+      [ac_cv_c_restrict=$ac_kw])
+     test "$ac_cv_c_restrict" != no && break
    done
   ])
  case $ac_cv_c_restrict in
Index: tests/mktests.sh
===================================================================
RCS file: /cvsroot/autoconf/autoconf/tests/mktests.sh,v
retrieving revision 1.45
diff -u -r1.45 mktests.sh
--- tests/mktests.sh    1 Apr 2006 15:57:02 -0000       1.45
+++ tests/mktests.sh    3 Apr 2006 16:40:05 -0000
@@ -121,7 +121,7 @@
 # - AC_FD_CC
 #   Is a number.
 #
-# - AC_PROG_CC, AC_C_(CONST|INLINE|VOLATILE), AC_PATH_XTRA
+# - AC_PROG_CC, AC_C_(CONST|VOLATILE), AC_PATH_XTRA
 #   Checked in semantics.
 #
 # - AC_CYGWIN, AC_CYGWIN32, AC_EMXOS2, AC_MING32, AC_EXEEXT, AC_OBJEXT
@@ -155,7 +155,7 @@
 ^AC_SEARCH_LIBS$
 ^(AC_TRY.*|AC_RUN_LOG)$
 ^AC_.*_IFELSE$
-^(AC_(PROG_CC|C_CONST|C_INLINE|C_RESTRICT|C_VOLATILE))$
+^(AC_(PROG_CC|C_CONST|C_VOLATILE))$
 ^AC_(CYGWIN|CYGWIN32|EMXOS2|MING32|EXEEXT|OBJEXT)$
 ^AC_PATH_XTRA$
 ^AC_SYS_RESTARTABLE_SYSCALLS$