Add assert

Author: corona10

Python/flowgraph.c

@@ -1314,8 +1314,8 @@ remove_redundant_deadstore(basicblock *bb)
         if (inst->i_opcode == STORE_FAST) {
             for (int j = i - 1; j >= 0; j--) {
                 cfg_instr *prev = &bb->b_instr[j];
+                assert(prev->i_loc.lineno <= inst->i_loc.lineno);
                 if (prev->i_loc.lineno != inst->i_loc.lineno) {
-                    // Invariant condition: lineno is always monotonically increasing.
                     break;
                 }
                 if (prev->i_opcode == STORE_FAST && prev->i_oparg == inst->i_oparg) {