| From: | Amit Khandekar <amitdkhan(dot)pg(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Auto-vectorization speeds up multiplication of large-precision numerics |
| Date: | 2020-09-07 07:10:49 |
| Message-ID: | CAJ3gD9ePT7NOSad=WymVvVwoNPLieT2ufddb7raaGMXyw5u89A@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, 7 Sep 2020 at 11:23, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> I wrote:
> > I made some cosmetic changes to this and committed it.
Thanks!
>
> BTW, poking at this further, it seems that the patch only really
> works for gcc. clang accepts the -ftree-vectorize switch, but
> looking at the generated asm shows that it does nothing useful.
> Which is odd, because clang does do loop vectorization.
>
> I tried adding -Rpass-analysis=loop-vectorize and got
>
> numeric.c:8341:3: remark: loop not vectorized: could not determine number of loop iterations [-Rpass-analysis=loop-vectorize]
> for (i2 = 0; i2 <= i; i2++)
Hmm, yeah that's unfortunate. My guess is that the compiler would do
vectorization only if 'i' is a constant, which is not true for our
case.
--
Thanks,
-Amit Khandekar
Huawei Technologies
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