From: Tom Lane <tgl@sss.pgh.pa.us>
To: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>
cc: pgsql-hackers@lists.postgresql.org
Subject: Re: Optimze usage of immutable functions as relation
In-reply-to: <18924.1564165560@sss.pgh.pa.us>
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Comments: In-reply-to Tom Lane <tgl@sss.pgh.pa.us>
	message dated "Fri, 26 Jul 2019 14:26:00 -0400"
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Date: Fri, 26 Jul 2019 14:40:35 -0400
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I wrote:
> * It would be useful for the commentary to point out that in principle we
> could pull up any immutable (or, probably, even just stable) expression;
> but we don't, (a) for fear of multiple evaluations of the result costing
> us more than we can save, and (b) because a primary goal is to let the
> constant participate in further const-folding, and of course that won't
> happen for a non-Const.

BTW, so far as I can see, none of the test cases demonstrate that such
further const-folding can happen.  Since this is all pretty processing-
order-sensitive, I think an explicit test that that's possible would
be a good idea.

			regards, tom lane