optimization for map in scalar context

Message-id: <20040224110257.GA5510@ethan>

p4raw-id: //depot/perl@22369

diff --git a/pp_ctl.c b/pp_ctl.c
index e91ff54..26fb164 100644 (file)
--- 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 */