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From: Tom Lane <[email protected]>
To: Jacob Champion <[email protected]>
Cc: Daniel Gustafsson <[email protected]>
Cc: [email protected]
Subject: Re: jsonapi: scary new warnings with LTO enabled
Date: Wed, 16 Apr 2025 19:28:44 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAOYmi+n+DHpaEV5hymhufutTgc+S=+pDQfXEUi4hMAV1eO8aTw@mail.gmail.com>
References: <[email protected]>
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Jacob Champion <[email protected]> writes:
> On Wed, Apr 16, 2025 at 4:04 PM Tom Lane <[email protected]> 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

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