| 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 00:22:08 |
| Message-ID: | 20190215002208.GA25042@alvherre.pgsql |
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| Lists: | pgsql-hackers |
On 2019-Feb-14, Tom Lane wrote:
> I think we need a clean test for __builtin_popcount(), and to be willing
> to use it if available, independently of -mpopcnt. Then separately we
> should test to see if -mpopcnt works, probably with the same
> infrastructure we use for checking for other compiler flags, viz
>
> # Optimization flags for specific files that benefit from vectorization
> PGAC_PROG_CC_VAR_OPT(CFLAGS_VECTOR, [-funroll-loops])
> PGAC_PROG_CC_VAR_OPT(CFLAGS_VECTOR, [-ftree-vectorize])
> + # Optimization flags for bit-twiddling
> + PGAC_PROG_CC_VAR_OPT(CFLAGS_POPCNT, [-mpopcnt])
> # We want to suppress clang's unhelpful unused-command-line-argument warnings
>
> 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.
Yeah, this works. I'll post the patch tomorrow.
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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