Preserve snapshot #0 PC for all traces (potential gcstep exit).

src/lj_snap.c

@@ -147,8 +147,7 @@ void lj_snap_add(jit_State *J)
   /* Merge if no ins. inbetween or if requested and no guard inbetween. */
   if (J->mergesnap ? !irt_isguard(J->guardemit) :
       (nsnap > 0 && J->cur.snap[nsnap-1].ref == J->cur.nins)) {
-    if (nsnap == 1 && J->parent == 0) {
-      /* But preserve snap #0 PC for root traces. */
+    if (nsnap == 1) {  /* But preserve snap #0 PC. */
       emitir_raw(IRT(IR_NOP, IRT_NIL), 0, 0);
       goto nomerge;
     }