[PATCH macros] Cache the results of checking compiler flag support in XORG_TESTSET_CFLAG

[Jon TURNEY]

Since checking all those warning flags takes an amount of time I find irritating,
here is an attempt at caching the results of checking compiler warning flag support

A couple of aspects which need definitely need review or testing:

* I've tried to get things right when not the first flag in the list of alternates is
supported, but this really needs testing with a compiler other than gcc

* The cache variable naming policy is a bit opaque me, so the names used may need corecting

* I've tried to be careful, but who knows what portability sins I have committed :-)

This change reduces the time to run the ./configure script produced from a configure.ac
containing just

AC_INIT([test], 1.0)
XORG_COMPILER_FLAGS
XORG_CWARNFLAGS
XORG_STRICT_OPTION
AC_OUTPUT()

from ~60s to ~20s on my cygwin machine, and from ~15s to ~9s on a linux VM running on the
same hardware

v2: AS_TR_SH transforms characters which are invalid in shell variable names, so we don't
have to use sed to transform spaces ourself

Signed-off-by: Jon TURNEY <jon.turney at dronecode.org.uk>
---
 xorg-macros.m4.in |   34 +++++++++++++++++++++-------------
 1 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/xorg-macros.m4.in b/xorg-macros.m4.in
index 8197eb6..9e6acf5 100644
--- a/xorg-macros.m4.in
+++ b/xorg-macros.m4.in
@@ -1457,11 +1457,12 @@ xorg_testset_save_CFLAGS="$CFLAGS"
 
 if test "x$xorg_testset_unknown_warning_option" = "x" ; then
 	CFLAGS="$CFLAGS -Werror=unknown-warning-option"
-	AC_MSG_CHECKING([if $CC supports -Werror=unknown-warning-option])
-	AC_COMPILE_IFELSE([AC_LANG_SOURCE([int i;])],
-	                  [xorg_testset_unknown_warning_option=yes],
-	                  [xorg_testset_unknown_warning_option=no])
-	AC_MSG_RESULT([$xorg_testset_unknown_warning_option])
+	AC_CACHE_CHECK([if $CC supports -Werror=unknown-warning-option],
+			xorg_cv_cc_flag_unknown_warning_option,
+			AC_COMPILE_IFELSE([AC_LANG_SOURCE([int i;])],
+					  [xorg_cv_cc_flag_unknown_warning_option=yes],
+					  [xorg_cv_cc_flag_unknown_warning_option=no]))
+	xorg_testset_unknown_warning_option=$xorg_cv_cc_flag_unknown_warning_option
 	CFLAGS="$xorg_testset_save_CFLAGS"
 fi
 
@@ -1470,11 +1471,12 @@ if test "x$xorg_testset_unused_command_line_argument" = "x" ; then
 		CFLAGS="$CFLAGS -Werror=unknown-warning-option"
 	fi
 	CFLAGS="$CFLAGS -Werror=unused-command-line-argument"
-	AC_MSG_CHECKING([if $CC supports -Werror=unused-command-line-argument])
-	AC_COMPILE_IFELSE([AC_LANG_SOURCE([int i;])],
-	                  [xorg_testset_unused_command_line_argument=yes],
-	                  [xorg_testset_unused_command_line_argument=no])
-	AC_MSG_RESULT([$xorg_testset_unused_command_line_argument])
+	AC_CACHE_CHECK([if $CC supports -Werror=unused-command-line-argument],
+			xorg_cv_cc_flag_unused_command_line_argument,
+			AC_COMPILE_IFELSE([AC_LANG_SOURCE([int i;])],
+					  [xorg_cv_cc_flag_unused_command_line_argument=yes],
+					  [xorg_cv_cc_flag_unused_command_line_argument=no]))
+	xorg_testset_unused_command_line_argument=$xorg_cv_cc_flag_unused_command_line_argument
 	CFLAGS="$xorg_testset_save_CFLAGS"
 fi
 
@@ -1491,12 +1493,18 @@ m4_foreach([flag], m4_cdr($@), [
 
 		CFLAGS="$CFLAGS ]flag["
 
+dnl Some hackery here since AC_CACHE_VAL can't handle a non-literal varname
 		AC_MSG_CHECKING([if $CC supports ]flag[])
-		AC_LINK_IFELSE([AC_LANG_PROGRAM([int i;])],
-		                  [supported=yes], [supported=no])
-		AC_MSG_RESULT([$supported])
+		cacheid=`AS_ECHO_N([xorg_cv_cc_flag_]flag[])`
+		AC_CACHE_VAL(AS_TR_SH($cacheid),
+			     [AC_LINK_IFELSE([AC_LANG_PROGRAM([int i;])],
+					     [eval AS_TR_SH($cacheid)=yes],
+					     [eval AS_TR_SH($cacheid)=no])])
+
 		CFLAGS="$xorg_testset_save_CFLAGS"
 
+		eval supported=$AS_TR_SH($cacheid)
+		AC_MSG_RESULT([$supported])
 		if test "$supported" = "yes" ; then
 			$1="$$1 ]flag["
 			found="yes"
-- 
1.7.5.1


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