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From: Tom Lane <[email protected]>
To: Heikki Linnakangas <[email protected]>
Cc: David Geier <[email protected]>
Cc: Matthias van de Meent <[email protected]>
Cc: pgsql-hackers <[email protected]>
Subject: Re: Reduce build times of pg_trgm GIN indexes
Date: Sun, 12 Apr 2026 14:05:02 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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Heikki Linnakangas <[email protected]> writes:
> Pushed 0001 as commit 6f5ad00ab7.

This commit has caused Coverity to start complaining that
most of ginExtractEntries() is unreachable:

*** CID 1691468:         Control flow issues  (DEADCODE)
/srv/coverity/git/pgsql-git/postgresql/src/backend/access/gin/ginutil.c: 495             in ginExtractEntries()
489     	/*
490     	 * Scan the items for any NULLs.  All NULLs are considered equal, so we
491     	 * just need to check and remember if there are any.  We remove them from
492     	 * the array here, and after deduplication, put back one NULL entry to
493     	 * represent them all.
494     	 */
>>>     CID 1691468:         Control flow issues  (DEADCODE)
>>>     Execution cannot reach this statement: "hasNull = false;".
495     	hasNull = false;
496     	if (nullFlags)
497     	{
498     		int32		numNonNulls = 0;
499     
500     		for (int32 i = 0; i < nentries; i++)

Evidently, it does not realize that the extractValueFn() can change
nentries from its initial value of zero.  I wouldn't be too surprised
if that's related to our casting of the pointer to uintptr_t --- that
may cause it to not see the passed pointer as a potential reference
mechanism.

I would just write that off as Coverity not being smart enough, except
that I'm worried that some compiler might make a similar deduction and
break the function completely.  Was the switch to a local variable
for nentries really a useful win performance-wise?

			regards, tom lane

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