+/* An op sequencer. We visit the ops in the order they're to execute. */
+
+STATIC void
+sequence(pTHX_ register const OP *o)
+{
+ dVAR;
+ SV *op;
+ char *key;
+ STRLEN len;
+ const OP *oldop = 0;
+ OP *l;
+
+ if (!o)
+ return;
+
+ op = newSVuv(PTR2UV(o));
+ key = SvPV(op, len);
+ if (hv_exists(Sequence, key, len))
+ return;
+
+ for (; o; o = o->op_next) {
+ op = newSVuv(PTR2UV(o));
+ key = SvPV(op, len);
+ if (hv_exists(Sequence, key, len))
+ break;
+
+ switch (o->op_type) {
+ case OP_STUB:
+ if ((o->op_flags & OPf_WANT) != OPf_WANT_LIST) {
+ hv_store(Sequence, key, len, newSVuv(++PL_op_seq), 0);
+ break;
+ }
+ goto nothin;
+ case OP_NULL:
+ if (oldop && o->op_next)
+ continue;
+ break;
+ case OP_SCALAR:
+ case OP_LINESEQ:
+ case OP_SCOPE:
+ nothin:
+ if (oldop && o->op_next)
+ continue;
+ hv_store(Sequence, key, len, newSVuv(++PL_op_seq), 0);
+ break;
+
+ case OP_MAPWHILE:
+ case OP_GREPWHILE:
+ case OP_AND:
+ case OP_OR:
+ case OP_DOR:
+ case OP_ANDASSIGN:
+ case OP_ORASSIGN:
+ case OP_DORASSIGN:
+ case OP_COND_EXPR:
+ case OP_RANGE:
+ hv_store(Sequence, key, len, newSVuv(++PL_op_seq), 0);
+ for (l = cLOGOPo->op_other; l && l->op_type == OP_NULL; l = l->op_next)
+ ;
+ sequence(aTHX_ l);
+ break;
+
+ case OP_ENTERLOOP:
+ case OP_ENTERITER:
+ hv_store(Sequence, key, len, newSVuv(++PL_op_seq), 0);
+ for (l = cLOOPo->op_redoop; l && l->op_type == OP_NULL; l = l->op_next)
+ ;
+ sequence(aTHX_ l);
+ for (l = cLOOPo->op_nextop; l && l->op_type == OP_NULL; l = l->op_next)
+ ;
+ sequence(aTHX_ l);
+ for (l = cLOOPo->op_lastop; l && l->op_type == OP_NULL; l = l->op_next)
+ ;
+ sequence(aTHX_ l);
+ break;
+
+ case OP_QR:
+ case OP_MATCH:
+ case OP_SUBST:
+ hv_store(Sequence, key, len, newSVuv(++PL_op_seq), 0);
+ for (l = cPMOPo->op_pmreplstart; l && l->op_type == OP_NULL; l = l->op_next)
+ ;
+ sequence(aTHX_ l);
+ break;
+
+ case OP_HELEM:
+ break;
+
+ default:
+ hv_store(Sequence, key, len, newSVuv(++PL_op_seq), 0);
+ break;
+ }
+ oldop = o;
+ }
+}
+
+STATIC UV
+sequence_num(pTHX_ const OP *o)
+{
+ dVAR;
+ SV *op,
+ **seq;
+ char *key;
+ STRLEN len;
+ if (!o) return 0;
+ op = newSVuv(PTR2UV(o));
+ key = SvPV(op, len);
+ seq = hv_fetch(Sequence, key, len, 0);
+ return seq ? SvUV(*seq): 0;
+}
+