optimization for map in scalar context

Message-id: <20040224110257.GA5510@ethan>

p4raw-id: //depot/perl@22369

1 files changed, 13 insertions, 2 deletions

diff --git a/pp_ctl.c b/pp_ctl.c
index e91ff540e0..26fb164a6b 100644
--- a/pp_ctl.c
+++ b/pp_ctl.c
@@ -939,8 +939,19 @@ PP(pp_mapwhile)
 	}
 	/* copy the new items down to the destination list */
 	dst = PL_stack_base + (PL_markstack_ptr[-2] += items) - 1;
-	while (items-- > 0)
-	    *dst-- = SvTEMP(TOPs) ? POPs : sv_mortalcopy(POPs);
+	if (gimme == G_ARRAY) {
+	    while (items-- > 0)
+		*dst-- = SvTEMP(TOPs) ? POPs : sv_mortalcopy(POPs);
+	}
+	else { 
+	    /* scalar context: we don't care about which values map returns
+	     * (we use undef here). And so we certainly don't want to do mortal
+	     * copies of meaningless values. */
+	    while (items-- > 0) {
+		POPs;
+		*dst-- = &PL_sv_undef;
+	    }
+	}
     }
     LEAVE;					/* exit inner scope */