From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
cc: Ants Aasma <ants.aasma@eesti.ee>, Heikki Linnakangas <hlinnaka@iki.fi>,
        Tomas Vondra <tomas.vondra@2ndquadrant.com>,
        PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: WIP: Faster Expression Processing v4
In-reply-to: <20170327152914.m3firc6rkx5tqtgo@alap3.anarazel.de>
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Comments: In-reply-to Andres Freund <andres@anarazel.de>
	message dated "Mon, 27 Mar 2017 08:29:14 -0700"
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Date: Mon, 27 Mar 2017 11:52:05 -0400
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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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