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Re: planner fails on HEAD

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Cc: PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: planner fails on HEAD
Date: 2011-12-04 22:55:41
Message-ID: 19320.1323039341@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
> it looks like gcc bug - gcc 4.5.1 20100924 (Red Hat 4.5.1) It was
> configured just with --enable-debug and --enable-cassert

Is this x86?  I can't reproduce it on x86_64.

It's fairly easy to get a set of values such that innerstartsel *should*
equal innerendsel; but if one value has been rounded to memory precision
and the other hasn't, the assert could certainly fail.

Some digging around yields the information that the gcc hackers do not
consider this a bug, or at least adamantly refuse to do anything about it:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=323
Comment 47 is particularly relevant to our situation:

	To summarize, this defect effectively states that:
	assert( (x/y) == (x/y) )
	may cause an assertion if compiled with optimization.

Also, http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45691#c4
indicates that an explicit cast to double should help.  Would
you check if the problem goes away if the Asserts are changed to

	Assert((double) outerstartsel <= (double) outerendsel);
	Assert((double) innerstartsel <= (double) innerendsel);

			regards, tom lane

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