Re: Missed compiler optimization issue in function select_rtable_names_for_explain

> How is the memset in select_rtable_names_for_explain a dead-store?
> Even memset
> calls could be optimized away from the EXPLAIN codepath I have a feeling it
> would have to be many in a tight loop for it to be measurable even?
>
> --
> Daniel Gustafsson

For the first question, I don't mean that the memset is the dead store.
I mean that the stores with value "0" after the memset are dead:

```

    dpns.subplans = NIL;
    dpns.ctes = NIL;
    dpns.appendrels = NULL;
```
since the memset has written zeroes to the object "dpns", and these
members are known to be zero.

For the second question, you are right, I don't really profile it or
measure the performance impact for it. I just think it's worthwhile to
improve codegen quality without affecting readability, as adopting
performance tips from some static analyzer.

Best regards, Hongyu.