Re: Speed up COPY FROM text/CSV parsing using SIMD

Hello,
On Wed, Nov 19, 2025 at 10:01 PM Nathan Bossart <nathandbossart(at)gmail(dot)com>
wrote:

> On Tue, Nov 18, 2025 at 05:20:05PM +0300, Nazir Bilal Yavuz wrote:
> > Thanks, done.
>
> I took a look at the v3 patches. Here are my high-level thoughts:
>
> + /*
> + * Parse data and transfer into line_buf. To get benefit from
> inlining,
> + * call CopyReadLineText() with the constant boolean variables.
> + */
> + if (cstate->simd_continue)
> + result = CopyReadLineText(cstate, is_csv, true);
> + else
> + result = CopyReadLineText(cstate, is_csv, false);
>
> I'm curious whether this actually generates different code, and if it does,
> if it's actually faster. We're already branching on cstate->simd_continue
> here.

I've compiled both versions with -O2 and confirmed they generate different
code. When simd_continue is passed as a constant to CopyReadLineText, the
compiler optimizes out the condition checks from the SIMD path.
A small benchmark on a 1GB+ file shows the expected benefit which is around
6% performance improvement.
I've attached the assembly outputs in case someone wants to check something
else.

Regards,
Ayoub Kazar