From: Tom Lane <tgl@sss.pgh.pa.us>
To: Jacob Champion <jacob.champion@enterprisedb.com>
cc: Daniel Gustafsson <daniel@yesql.se>, pgsql-hackers@lists.postgresql.org
Subject: Re: jsonapi: scary new warnings with LTO enabled
In-reply-to: <CAOYmi+n+DHpaEV5hymhufutTgc+S=+pDQfXEUi4hMAV1eO8aTw@mail.gmail.com>
References: <2074634.1744839761@sss.pgh.pa.us> <0A3CF5C4-9947-42E3-89A9-34FCF7BA95BA@yesql.se> <2078511.1744841564@sss.pgh.pa.us> <DCD56158-A642-4954-87FF-9DAD5425F3FF@yesql.se> <2084687.1744844690@sss.pgh.pa.us> <CAOYmi+n+DHpaEV5hymhufutTgc+S=+pDQfXEUi4hMAV1eO8aTw@mail.gmail.com>
Comments: In-reply-to Jacob Champion <jacob.champion@enterprisedb.com>
	message dated "Wed, 16 Apr 2025 16:09:40 -0700"
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Date: Wed, 16 Apr 2025 19:28:44 -0400
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Jacob Champion <jacob.champion@enterprisedb.com> writes:
> On Wed, Apr 16, 2025 at 4:04 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Looking through all of the callers of freeJsonLexContext, quite
>> a lot of them use local JsonLexContext structs, and probably some
>> of them are more performance-critical than these.  So that raises
>> the question of why are we seeing warnings for only these call
>> sites?

> Yeah, I had the same question...

After making another pass through the callers of freeJsonLexContext,
I observe that the warnings appear in callers that use a local
variable *and* contain goto statements.  So I'm betting that the
presence of goto's causes the LTO optimizer to pull in its horns
quite a bit and thereby fail to detect the flag correlation.

>> Maybe there is a more elegant way to suppress them.

> Can we brute-force ignore this particular warning site with a #pragma
> (suggested in [1])?

That's surely not elegant :-(.  However, I don't especially want to
rewrite away the goto's in these callers ...

			regards, tom lane