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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: Ants Aasma <ants.aasma@eesti.ee>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: WIP: Faster Expression Processing v4
Date: Mon, 27 Mar 2017 11:52:05 -0400
Message-ID: <31039.1490629925@sss.pgh.pa.us> (raw)
In-Reply-To: <20170327152914.m3firc6rkx5tqtgo@alap3.anarazel.de>
References: <5768.1490458935@sss.pgh.pa.us>
	<20170325222202.uz6evsjqrtwjnql6@alap3.anarazel.de>
	<CA+CSw_uq4OeY7i5u7=XeXXpJa0dMjfztP6FXrxQct-u=9vXJLA@mail.gmail.com>
	<3CC5B4C5-3ADB-4296-A04B-64F594A4CE4F@anarazel.de>
	<23529.1490500305@sss.pgh.pa.us>
	<20170326035927.5mubkfdtaqlrgm2d@alap3.anarazel.de>
	<20170327054314.qo6xsnlk7jcb7u2c@alap3.anarazel.de>
	<15684.1490621623@sss.pgh.pa.us>
	<20170327151750.dnpxtkjjade7kiv6@alap3.anarazel.de>
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	<20170327152914.m3firc6rkx5tqtgo@alap3.anarazel.de>
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As to the point of whether it actually helps or not ...

on gcc 6.3.1 (Fedora 25), yes it does.  Seems to be one "jmp *something"
per EEO_NEXT or EEO_JUMP.

on gcc 4.4.7 (RHEL 6), it makes things *WORSE*.  We go from about half of
the dispatches getting routed through a common location, to *all* of them
(except one; for some odd reason the first EEO_NEXT in EEOP_NULLIF
survives as a separate jump).  This seems like a bug, but there it is.

So this means we'd need some serious research to decide whether to apply
it.  And I'm suspecting we'd end up with a compiler version test.

			regards, tom lane


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