Re: Using POPCNT and other advanced bit manipulation instructions

From: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Using POPCNT and other advanced bit manipulation instructions
Date: 2019-02-15 14:54:25
Message-ID: 20190215145425.GA32071@alvherre.pgsql
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On 2019-Feb-14, Tom Lane wrote:

> Then the correct test to see if we want to build pg_popcount.c (BTW,
> please pick a less generic name for that) and the choose function
> is whether we have *both* HAVE__BUILTIN_POPCOUNT and nonempty
> CFLAGS_POPCNT.

I used pg_bitutils_sse42.c to host the specially-compiled functions.
The name is not entirely correct, but seems clear enough.

I noticed in Compiler Explorer that some (ancient?) Power cpus
implement instruction "popcntb", and GCC support for those uses
-mpopcntb switch enabling __builtin_popcount() to use it. I added the
switch to configure.in but I'm not sure how well that will work ... I
don't know if this is represented in buildfarm.

--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Attachment Content-Type Size
0001-Fix-compiler-builtin-usage-in-new-pg_bitutils.c.patch text/x-diff 29.8 KB

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