On Thu, 29 May 2025 at 14:14, Tom Lane <t...@sss.pgh.pa.us> wrote: > -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. [0] https://www.postgresql.org/message-id/flat/2eda015b-7dff-47fd-d5e2-f1a9899b90a6%40postgrespro.ru -- Best regards, Maxim Orlov.
v1-0001-Use-volatile-to-avoid-unspecified-behavior-in-PG_.patch
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