Fix data-flow analysis for BC_ITERL.

src/lj_snap.c

@@ -192,7 +192,7 @@ static BCReg snap_usedef(jit_State *J, uint8_t *udf,
     handle_jump: {
       BCReg minslot = bc_a(ins);
       if (op >= BC_FORI && op <= BC_JFORL) minslot += FORL_EXT;
-      else if (op >= BC_ITERL && op <= BC_JITERL) minslot += bc_b(pc[-1])-1;
+      else if (op >= BC_ITERL && op <= BC_JITERL) minslot += bc_b(pc[-2])-1;
       else if (op == BC_UCLO) { pc += bc_j(ins); break; }
       for (s = minslot; s < maxslot; s++) DEF_SLOT(s);
       return minslot < maxslot ? minslot : maxslot;