[PATCH 00/11] C++26 [simd]

[Matthias Kretz]

Tomasz Kaminski [Monday, 20 October 2025, 15:43:50 CEST]:
> On Mon, Oct 20, 2025 at 3:32 PM Matthias Kretz <m.kretz@gsi.de> wrote:
> > Let me start with your last point:
> > 
> > Tomasz Kaminski [Monday, 20 October 2025, 11:24:55 CEST]:
> > > I think I would prefer the direction of just using plain
> > > __glibcxx_assert
> > > for libstdc++, and not innovate a new error checking
> > > strategies.
> > 
> > Yes. I guess the simd PR should just use __glibcxx_assert and I should
> > open a
> > separate PR that would innovate new precondition checking consistently all
> > over libstdc++. That said, I don't want to miss these error messages in my
> > simd code. They have been helpful.
> 
> We have hardened preconditions in c++26, that will turn some of the checks
> into contract violations. I am a bit afraid of tying our hands there, and
> would
> prefer to not deviate until we see what will happen with that.

Sure. Contracts will certainly change the picture. And if we have a contracts 
implementation that warns on unconditional precondition violation in constant 
propagation then we don't need to do any of what I said in the library.

I guess, that's part of the point I'm trying to make, though. That this is a 
feature we want to have. Once we have contracts, that's where it belongs.

IIUC, hardened preconditions can be described as https://compiler-explorer.com/z/8sjf3x9rT. So as I see it there could be 3 macros (as long as 
we don't have contracts in the language)

__glibcxx_assert(expr)
__glibcxx_precondition(expr)
__glibcxx_hardened_precondition(expr)

- Matthias

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 Dr. Matthias Kretz                           https://mattkretz.github.io
 GSI Helmholtz Center for Heavy Ion Research               https://gsi.de
 std::simd
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