Missed compiler optimization issue in function select_rtable_names_for_explain

Hi everyone,

I'm a compiler developer working on detecting missed optimization in
real-world applications. Recently, we found that LLVM missed a dead
store elimination optimization in the PostgreSQL code
<https://github.com/postgres/postgres/blob/c37267162e889fe783786b9e28d1b65b82365a00/src/backend/utils/adt/ruleutils.c#L3794>
(https://github.com/postgres/postgres/blob/master/src/backend/utils/adt/ruleutils.c#L3794)
in the master branch.

For the example below:

```

int dst[128];

memset(dst, 0, 128);

*unrelated = some_value;

dst[1] = 0;

dst[2] = 0;

```

LLVM cannot eliminate the useless stores after memset since the store to
"unrelated" clobbers. But if we put the stores to "dst" ahead of the
store to "unrelated", we could prevent confusing the compiler. See also
the compiler explorer link: https://godbolt.org/z/P9jnKod3v and the
issue of LLVM: https://github.com/llvm/llvm-project/issues/88632

To improve the codegen quality, I think it's also possible to modify the
source code, changing the order of initialization of the member, to get
better optimization. But I don't know whether this can be considered as
a bug, thus post the issue here.

If anyone could confirm this problem or post a patch for it, let me know
please. Thanks!

Best regards. Hongyu.