Don't try to store PL_sv_undef in pads. (For now)

p4raw-id: //depot/perl@26494

diff --git a/op.c b/op.c
index cb9b0e6..1e8e43a 100644 (file)
--- a/op.c
+++ b/op.c
@@ -6794,6 +6794,18 @@ Perl_peep(pTHX_ register OP *o)
                    SvREADONLY_on(PAD_SVl(ix));
                    SvREFCNT_dec(cSVOPo->op_sv);
                }
+               else if (o->op_type == OP_CONST
+                        && cSVOPo->op_sv == &PL_sv_undef) {
+                   /* PL_sv_undef is hack - it's unsafe to store it in the
+                      AV that is the pad, because av_fetch treats values of
+                      PL_sv_undef as a "free" AV entry and will merrily
+                      replace them with a new SV, causing pad_alloc to think
+                      that this pad slot is free. (When, clearly, it is not)
+                   */
+                   SvOK_off(PAD_SVl(ix));
+                   SvPADTMP_on(PAD_SVl(ix));
+                   SvREADONLY_on(PAD_SVl(ix));
+               }
                else {
                    SvREFCNT_dec(PAD_SVl(ix));
                    SvPADTMP_on(cSVOPo->op_sv);