add OPpDEREFed flag to avoid double mg_get()

    The previous commit made various ops such as rv2av unconditionally do
    an SvGETMAGIC(). Under some circumstances this could cause a double
    mg_get() (and hence double FETCH etc). In particular, when the
    proceeding op was something like aelem with OPpDEREF, the aelem would
    call vivify_ref(), which would call magic. So in peep(), mark
    OP_RV2[SAH]V ops with the new OPpDEREFed flag if the preceding op was
    OPpDEREF. Then use this flag to avoid a second dose of magic.

    Note that RV2GV probably needs this flag too, but there weren't any
    spare private flag bits left for that op (I think).

1 files changed, 5 insertions, 0 deletions

diff --git a/dump.c b/dump.c
index 631f37cbb2..46af01a8db 100644
--- a/dump.c
+++ b/dump.c
@@ -928,6 +928,11 @@ Perl_do_op_dump(pTHX_ I32 level, PerlIO *file, const OP *o)
 		if (o->op_private & OPpMAYBE_LVSUB)
 		    sv_catpv(tmpsv, ",MAYBE_LVSUB");
 	    }
+
+	    if ((optype==OP_RV2SV || optype==OP_RV2AV || optype==OP_RV2HV)
+		    && (o->op_private & OPpDEREFed))
+		sv_catpv(tmpsv, ",DEREFed");
+
 	    if (optype == OP_AELEM || optype == OP_HELEM) {
 		if (o->op_private & OPpLVAL_DEFER)
 		    sv_catpv(tmpsv, ",LVAL_DEFER");