[PATCH] c++: implement C++17 hardware interference size

[Matthias Kretz]

On Saturday, 17 July 2021 15:32:42 CEST Jonathan Wakely wrote:
> On Sat, 17 Jul 2021, 09:15 Matthias Kretz, <m.kretz@gsi.de> wrote:
> > If somebody writes a library with `keep_apart` in the public API/ABI then
> > you're right.
> 
> Yes, it's fine if those constants don't affect anything across module
> boundaries.

I believe a significant fraction of hardware interference size usage will be 
internal.

> > The developer who wants his code to be included in a distro should care
> > about
> > binary distribution. If his code has an ABI issue, that's a bug he needs
> > to
> > fix. It's not the fault of the packager.
> 
> Yes but in practice it's the packagers who have to deal with the bug
> reports, analyze the problem, and often fix the bug too. It might not be
> the packager's fault but it's often their problem 

I can imagine. But I don't think requiring users to specify the value 
according to what -mtune suggests will improve things. Users will write a 
configure/cmake/... macro to parse the value -mtune prints and pass that on 
the command line (we'll soon find this solution on SO 😜). I.e. things are 
likely to be even more broken.

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 Dr. Matthias Kretz                           https://mattkretz.github.io
 GSI Helmholtz Centre for Heavy Ion Research               https://gsi.de
 std::experimental::simd              https://github.com/VcDevel/std-simd
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