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, 14 insertions, 0 deletions

diff --git a/op.c b/op.c
index 40ef4bcd3d..da0ad2c710 100644
--- a/op.c
+++ b/op.c
@@ -8877,6 +8877,20 @@ Perl_peep(pTHX_ register OP *o)
 	    }
 	    break;
 	}
+	case OP_RV2SV:
+	case OP_RV2AV:
+	case OP_RV2HV:
+	    if (oldop
+		 && (  oldop->op_type == OP_AELEM
+		    || oldop->op_type == OP_PADSV
+		    || oldop->op_type == OP_RV2SV
+		    || oldop->op_type == OP_RV2GV
+		    || oldop->op_type == OP_HELEM
+		    )
+	         && (oldop->op_private & OPpDEREF)
+	    ) {
+		o->op_private |= OPpDEREFed;
+	    }
 
 	case OP_SORT: {
 	    /* will point to RV2AV or PADAV op on LHS/RHS of assign */