longlong: tune, particularly for common case of c99

* m4/longlong.m4 (AC_TYPE_LONG_LONG_INT): Don't bother compiling
or running anything if c99, or if unsigned long long int does not
work.  In either case, we know the answer without further tests.
Do not compile _AC_TYPE_LONG_LONG_SNIPPET twice.  Instead, compile
it at most once, and use its results for both long long int and
unsigned long long int.  This is more likely to be efficient in
the common case where the program wants to check for both long
long int and unsigned long long int.
(AC_TYPE_UNSIGNED_LONG_LONG_INT): Don't bother compiling if c99,
since the answer is already known.

1 files changed, 43 insertions, 37 deletions

diff --git a/m4/longlong.m4 b/m4/longlong.m4
index a4d95aa1ab..04c8303bca 100644
--- a/m4/longlong.m4
+++ b/m4/longlong.m4
@@ -1,4 +1,4 @@
-# longlong.m4 serial 14
+# longlong.m4 serial 15
 dnl Copyright (C) 1999-2007, 2009-2011 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -7,8 +7,8 @@ dnl with or without modifications, as long as this notice is preserved.
 dnl From Paul Eggert.
 
 # Define HAVE_LONG_LONG_INT if 'long long int' works.
-# This fixes a bug in Autoconf 2.61, but can be removed once we
-# assume 2.62 everywhere.
+# This fixes a bug in Autoconf 2.61, and can be faster
+# than what's in Autoconf 2.62 through 2.68.
 
 # Note: If the type 'long long int' exists but is only 32 bits large
 # (as on some very old compilers), HAVE_LONG_LONG_INT will not be
@@ -16,35 +16,38 @@ dnl From Paul Eggert.
 
 AC_DEFUN([AC_TYPE_LONG_LONG_INT],
 [
+  AC_REQUIRE([AC_TYPE_UNSIGNED_LONG_LONG_INT])
   AC_CACHE_CHECK([for long long int], [ac_cv_type_long_long_int],
-    [AC_LINK_IFELSE(
-       [_AC_TYPE_LONG_LONG_SNIPPET],
-       [dnl This catches a bug in Tandem NonStop Kernel (OSS) cc -O circa 2004.
-        dnl If cross compiling, assume the bug isn't important, since
-        dnl nobody cross compiles for this platform as far as we know.
-        AC_RUN_IFELSE(
-          [AC_LANG_PROGRAM(
-             [[@%:@include <limits.h>
-               @%:@ifndef LLONG_MAX
-               @%:@ define HALF \
-                        (1LL << (sizeof (long long int) * CHAR_BIT - 2))
-               @%:@ define LLONG_MAX (HALF - 1 + HALF)
-               @%:@endif]],
-             [[long long int n = 1;
-               int i;
-               for (i = 0; ; i++)
-                 {
-                   long long int m = n << i;
-                   if (m >> i != n)
-                     return 1;
-                   if (LLONG_MAX / 2 < m)
-                     break;
-                 }
-               return 0;]])],
-          [ac_cv_type_long_long_int=yes],
-          [ac_cv_type_long_long_int=no],
-          [ac_cv_type_long_long_int=yes])],
-       [ac_cv_type_long_long_int=no])])
+     [ac_cv_type_long_long_int=yes
+      if test "x${ac_cv_prog_cc_c99-no}" = xno; then
+        ac_cv_type_long_long_int=$ac_cv_type_unsigned_long_long_int
+        if test $ac_cv_type_long_long_int = yes; then
+          dnl Catch a bug in Tandem NonStop Kernel (OSS) cc -O circa 2004.
+          dnl If cross compiling, assume the bug is not important, since
+          dnl nobody cross compiles for this platform as far as we know.
+          AC_RUN_IFELSE(
+            [AC_LANG_PROGRAM(
+               [[@%:@include <limits.h>
+                 @%:@ifndef LLONG_MAX
+                 @%:@ define HALF \
+                          (1LL << (sizeof (long long int) * CHAR_BIT - 2))
+                 @%:@ define LLONG_MAX (HALF - 1 + HALF)
+                 @%:@endif]],
+               [[long long int n = 1;
+                 int i;
+                 for (i = 0; ; i++)
+                   {
+                     long long int m = n << i;
+                     if (m >> i != n)
+                       return 1;
+                     if (LLONG_MAX / 2 < m)
+                       break;
+                   }
+                 return 0;]])],
+            [],
+            [ac_cv_type_long_long_int=no])
+        fi
+      fi])
   if test $ac_cv_type_long_long_int = yes; then
     AC_DEFINE([HAVE_LONG_LONG_INT], [1],
       [Define to 1 if the system has the type `long long int'.])
@@ -52,8 +55,8 @@ AC_DEFUN([AC_TYPE_LONG_LONG_INT],
 ])
 
 # Define HAVE_UNSIGNED_LONG_LONG_INT if 'unsigned long long int' works.
-# This fixes a bug in Autoconf 2.61, but can be removed once we
-# assume 2.62 everywhere.
+# This fixes a bug in Autoconf 2.61, and can be faster
+# than what's in Autoconf 2.62 through 2.68.
 
 # Note: If the type 'unsigned long long int' exists but is only 32 bits
 # large (as on some very old compilers), AC_TYPE_UNSIGNED_LONG_LONG_INT
@@ -64,10 +67,13 @@ AC_DEFUN([AC_TYPE_UNSIGNED_LONG_LONG_INT],
 [
   AC_CACHE_CHECK([for unsigned long long int],
     [ac_cv_type_unsigned_long_long_int],
-    [AC_LINK_IFELSE(
-       [_AC_TYPE_LONG_LONG_SNIPPET],
-       [ac_cv_type_unsigned_long_long_int=yes],
-       [ac_cv_type_unsigned_long_long_int=no])])
+    [ac_cv_type_unsigned_long_long_int=yes
+     if test "x${ac_cv_prog_cc_c99-no}" = xno; then
+       AC_LINK_IFELSE(
+         [_AC_TYPE_LONG_LONG_SNIPPET],
+         [],
+         [ac_cv_type_unsigned_long_long_int=no])
+     fi])
   if test $ac_cv_type_unsigned_long_long_int = yes; then
     AC_DEFINE([HAVE_UNSIGNED_LONG_LONG_INT], [1],
       [Define to 1 if the system has the type `unsigned long long int'.])