autoconf: prefer an unrolled loop for trivial AC_CHECK_HEADERS

An unrolled loop avoids the cost of spawning sed in AS_TR_SH and
AS_TR_CPP.  Prefer it if there is nothing in the second and third
argument of AC_CHECK_HEADERS and the first argument is a literal.

* lib/autoconf/headers.m4 (AC_CHECK_HEADERS): Unroll loop if safe.
(_AC_CHECK_HEADERS): Move basic implementation here.
(AC_CHECK_INCLUDES_DEFAULT): Remove unnecessary arguments after the first.

Signed-off-by: Paolo Bonzini <bonzini@gnu.org>
Message-Id: <1477933688-4884-3-git-send-email-bonzini@gnu.org>
[eblake: perform AC_CHECK_HEADERS_ONCE changes separately, use
dnl to reduce generated blank lines]
Signed-off-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

diff --git a/lib/autoconf/headers.m4 b/lib/autoconf/headers.m4
index 5f4ab4a858e57e6fd1121667ceaa6dc334d58cee..8e2dbb02eedc1fc0e2dfbfa691dc65b840e8169c 100644 (file)
--- a/lib/autoconf/headers.m4
+++ b/lib/autoconf/headers.m4
@@ -185,12 +185,17 @@ m4_define([AH_CHECK_HEADERS],
 # header.  Either ACTION may include `break' to stop the search.
 AC_DEFUN([AC_CHECK_HEADERS],
 [m4_map_args_w([$1], [_AH_CHECK_HEADER(], [)])]dnl
-[AS_FOR([AC_header], [ac_header], [$1],
-[AC_CHECK_HEADER(AC_header,
-                [AC_DEFINE_UNQUOTED(AS_TR_CPP([HAVE_]AC_header)) $2],
-                [$3], [$4])dnl])
+[m4_if([$2$3]AS_LITERAL_IF([$1], [[yes]], [[no]]), [yes],
+       [m4_map_args_w([$1], [_$0(], [, [], [], [$4])])],
+       [AS_FOR([AC_header], [ac_header], [$1], [_$0(AC_header, [$2], [$3], [$4])])])dnl
 ])# AC_CHECK_HEADERS
 
+m4_define([_AC_CHECK_HEADERS],
+[AC_CHECK_HEADER([$1],
+                [AC_DEFINE_UNQUOTED(AS_TR_CPP([HAVE_]$1)) $2],
+                [$3], [$4])dnl
+])
+
 
 # _AC_CHECK_HEADER_ONCE(HEADER-FILE)
 # ----------------------------------
@@ -285,8 +290,7 @@ ac_includes_default="\
 #endif"
 ])]dnl
 [_AC_CHECK_HEADERS_ONCE(
-  [sys/types.h sys/stat.h strings.h inttypes.h stdint.h unistd.h],
-  [], [], [$ac_includes_default])]dnl
+  [sys/types.h sys/stat.h strings.h inttypes.h stdint.h unistd.h])]dnl
 dnl For backward compatibility, provide unconditional AC_DEFINEs of
 dnl HAVE_STDLIB_H, HAVE_STRING_H, and STDC_HEADERS.
 [AC_DEFINE([HAVE_STDLIB_H], [1],