add sv_set_undef() API function

This function is equivalent to sv_setsv(sv, &PL_sv_undef), but more
efficient.

Also change the obvious places in the core to use the new idiom.

1 files changed, 1 insertions, 1 deletions

diff --git a/pp.c b/pp.c
index ce589a0858..d406ee11fe 100644
--- a/pp.c
+++ b/pp.c
@@ -3249,7 +3249,7 @@ PP(pp_length)
 	}
     } else {
 	if (!SvPADTMP(TARG)) {
-	    sv_setsv_nomg(TARG, &PL_sv_undef);
+            sv_set_undef(TARG);
 	} else { /* TARG is on stack at this point and is overwriten by SETs.
                    This branch is the odd one out, so put TARG by default on
                    stack earlier to let local SP go out of liveness sooner */