Re: Warning -Wclobbered in PG_TRY(...)

-Wclobbered would be really useful if it worked --- but sadly,
on practically all gcc and clang versions, those warnings have
nearly nothing to do with reality.  We typically ignore them.

Yes, in the vast majority of cases. But I believe this is not one of them. Actually, we do 

not adhere to the C language standard for a setjump/logjump. Notice how the 

non-volatile local variable "bool dorethrow##" utilized in the setjump/logjump block. 

This topic reminds me of [0].

In fact, we do not receive a warning for a C-lang build because the compiler does not 

appear to be "smart" enough to put this variable in a register. I ran a synthetic test 

equivalent to PG_TRY using godbolt.org, and the final code was the same whether 

the volatile qualifier was used or not. This is not the case with the C++ build. If the 

volatile qualifier is not used, the compiler optimizes this line and puts it in a register, 

and we get a warning. And to get rid of this warning, you need to either turn it off via 

the pragma directive, write your own version of PG_TRY with a volatile type qualifier, 

or patch Postgres. None of these solutions sound good to me. You may be wondering 

who will write Postgres extensions in C++. Having two different runtimes is absolute 

misery, and I completely agree. However, such extensions already exist; for example, 

pg_duckdb. AFAICS, it is quite popular in our area.

So, to be safe, we should follow the standard and include a volatile qualifier here. It 

really costs us nothing; the resulting code will be identical for C, and we'll avoid any 

future issues. In the case of C++, it will also resolve the warning.

Don't consider me as something of a formalist or someone who wants to make 

mountains out of molehills. I just want to make things better. PFA trivial patch.