[clang] [clang] Introduce __builtin_splatvector (PR #212758)

[Paul Osmialowski via cfe-commits]

pawosm-arm wrote:

> > > > > Is there even a platform-generic type for scalable vectors yet?
> > > > 
> > > > 
> > > > Sadly, no.
> > > 
> > > 
> > > That seems like the thing we should solve first. After that I wouldn't be surprised if we didn't need this builtin at all.
> > 
> > 
> > No, it's the other way round. When I tried to introduce a platform-generic vector type, one of the comments was we should first improve builtin coverage of the sizeless vector types...
> 
> This is basically adding `VectorOfT(T)` though

Does it cover the same applicability?

> (assuming we end up designing a scalable vector type in a similar way to `ext_vector_type`)

We can't assume that. There was a lot of opposition and practical obstacles when I'd attempted to extend `ext_vector_type` to cover sizeless vector types.

> We don't need another builtin for that.

If others agree, I'm closing it.

https://github.com/llvm/llvm-project/pull/212758