Re: define pg_structiszero(addr, s, r)

On Fri, Nov 08, 2024 at 11:18:09PM +1300, David Rowley wrote:
> I'm slightly worried due to the current rate we're receiving cleanup
> suggestions that someone might come along and think they'd be doing us
> a favour by submitting a patch to "fixup the inefficient bitwise-ORs
> and use boolean-OR". Maybe a comment like the following might prevent
> that from happening.

Not sure, but OK by me to tweak things more.

> Can you share your test case for this?  I tried with [1] and the
> latest gcc does not seem to be smart enough to figure this out.  I
> tried adding some additional len checks that the compiler can use as a
> cue and won't need to emit code for the checks providing the function
> does get inlined. That was enough to get the compiler to not emit the
> loops when they'll not be used. See the -DCHECK_LEN flag I'm passing
> in the 2nd compiler window. I just don't know if putting something
> like that into the code is a good idea as if the function wasn't
> inlined for some reason, the extra len checks would have to be
> compiled into the function.

Feel free to use that (I hope it works), and see the difference once
the aligned structure is 121 bytes or more:
https://godbolt.org/z/94393nPGG

At least, I can see that the SIMD loop is ignored.
--
Michael