diff --git a/ChangeLog b/ChangeLog
index b686759bdd..22c41af9a2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+Thu Jan 12 13:51:00 2012  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* cont.c (cont_restore_0): prevent optimizing out `sp'. sp is used for
+	  reserving a memory space with ALLOCA_N for restoring machine stack
+	  stored in cont->machine_stack, but clang optimized out it (and
+	  maybe #5851 is also caused by this).
+	  This affected TestContinuation#test_check_localvars.
+
+	* cont.c (cont_restore_1): revert workaround introduced in r32201.
+
 Thu Jan 12 02:14:43 2012  Ayumu AIZAWA  <ayumu.aizawa@gmail.com>
 
 	* object.c: Added examples for Object#is_a? and
diff --git a/cont.c b/cont.c
index 69c32c7919..e2f01c49e6 100644
--- a/cont.c
+++ b/cont.c
@@ -676,10 +676,9 @@ cont_restore_1(rb_context_t *cont)
     }
 #endif
     if (cont->machine_stack_src) {
-	size_t i;
 	FLUSH_REGISTER_WINDOWS;
-	for (i = 0; i < cont->machine_stack_size; i++)
-	    cont->machine_stack_src[i] = cont->machine_stack[i];
+	MEMCPY(cont->machine_stack_src, cont->machine_stack,
+		VALUE, cont->machine_stack_size);
     }
 
 #ifdef __ia64
@@ -749,7 +748,7 @@ cont_restore_0(rb_context_t *cont, VALUE *addr_in_prev_frame)
 	    if (&space[0] > end) {
 # ifdef HAVE_ALLOCA
 		volatile VALUE *sp = ALLOCA_N(VALUE, &space[0] - end);
-		(void)sp;
+		space[0] = *sp;
 # else
 		cont_restore_0(cont, &space[0]);
 # endif
@@ -765,7 +764,7 @@ cont_restore_0(rb_context_t *cont, VALUE *addr_in_prev_frame)
 	    if (&space[STACK_PAD_SIZE] < end) {
 # ifdef HAVE_ALLOCA
 		volatile VALUE *sp = ALLOCA_N(VALUE, end - &space[STACK_PAD_SIZE]);
-		(void)sp;
+		space[0] = *sp;
 # else
 		cont_restore_0(cont, &space[STACK_PAD_SIZE-1]);
 # endif