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, 2 insertions, 1 deletions

diff --git a/pp_hot.c b/pp_hot.c
index d5c13fecd9..a8c06b85ae 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -820,7 +820,8 @@ PP(pp_rv2av)
     const bool is_pp_rv2av = PL_op->op_type == OP_RV2AV;
     const svtype type = is_pp_rv2av ? SVt_PVAV : SVt_PVHV;
 
-    SvGETMAGIC(sv);
+    if (!(PL_op->op_private & OPpDEREFed))
+	SvGETMAGIC(sv);
     if (SvROK(sv)) {
 	tryAMAGICunDEREF_var(is_pp_rv2av ? to_av_amg : to_hv_amg);