Index: ChangeLog
===================================================================
--- ChangeLog
+++ ChangeLog
@@ -1,5 +1,11 @@
+2011-06-30  Reinhard Max  <max@suse.de>
+
+	* unix/configure.in: Add a volatile declaration to the test for
+	TCL_STACK_GROWS_UP to prevent gcc 4.6 from producing invalid
+	results due to aggressive optimisation.
+
 2011-06-23  Don Porter  <dgp@users.sourceforge.net>
 
 	*** 8.5.10 TAGGED FOR RELEASE ***
 
 	* changes:	Update for 8.5.10 release.

Index: unix/configure
===================================================================
--- unix/configure
+++ unix/configure
@@ -18703,14 +18703,16 @@
 cat >>conftest.$ac_ext <<_ACEOF
 /* end confdefs.h.  */
 
 	int StackGrowsUp(int *parent) {
 	    int here;
+	    volatile int result;
 	    if (parent)
-		return (&here < parent);
+		result = (&here < parent);
 	    else
-		return StackGrowsUp(&here);
+		result = StackGrowsUp(&here);
+	    return result;
 	}
 	int main (int argc, char *argv[]) {
 	    return StackGrowsUp(0);
 	}
 

Index: unix/configure.in
===================================================================
--- unix/configure.in
+++ unix/configure.in
@@ -703,14 +703,16 @@
 
 AC_CACHE_CHECK([if the C stack grows upwards in memory], tcl_cv_stack_grows_up, [
     AC_TRY_RUN([
 	int StackGrowsUp(int *parent) {
 	    int here;
+	    volatile int result;
 	    if (parent)
-		return (&here < parent);
+		result = (&here < parent);
 	    else
-		return StackGrowsUp(&here);
+		result = StackGrowsUp(&here);
+	    return result;
 	}
 	int main (int argc, char *argv[]) {
 	    return StackGrowsUp(0);
 	}
     ], tcl_cv_stack_grows_up=yes, tcl_cv_stack_grows_up=no,