Re: [PATCH] audo-detect and use -moutline-atomics compilation flag for aarch64

On 10/09/2020 09:37, Zidenberg, Tsahi wrote:
> On 08/09/2020, 1:01, "Tom Lane" <tgl@sss.pgh.pa.us> wrote:
> 
>      > I wonder what version of gcc you intend this for.  AFAICS, older
>      > gcc versions lack this flag at all, while newer ones have it on
>      > by default.
> 
> 
> (previously sent private reply, sorry)
> 
> The moutline-atomics flag showed substantial enough improvements
> that it has been backported to GCC 9, 8 and there is a gcc-7 branch in
> the works.
> Ubuntu has integrated this in 20.04, Amazon Linux 2 supports it,
> with other distributions including Ubuntu 18.04 and Debian on the way.
> all distributions, including the upcoming Ubuntu with GCC-10, have
> moutline-atomics turned off by default.

If it's a good idea to use -moutline-atomics, I would expect the 
compiler or distribution to enable it by default. And as you pointed 
out, many have. For the others, there are probably reasons they haven't, 
like begin conservative in general. Whatever the reasons, IMHO we should 
not second-guess them.

I'm marking this as Rejected in the commitfest. But thanks for the 
benchmarking, that is valuable information nevertheless.

- Heikki