[llvm] [ADT] Add DenseSet(llvm::from_t, Range) (PR #131832)

[David Blaikie via llvm-commits]

dwblaikie wrote:

> > Other people feel strongly otherwise?
> 
> I'm fine with that too, but I'm not entirely convinced that this is a better convention than a helper function or a 'static constructor function' like `DenseSet<Foo>::fromRange(...)`. Or put it differently, is it work aligning with C++ stuff that we are unlikely to adopt in the future?

Even if we don't adopt ranges wholesale, it seems like these ctors (on standard types) would be pretty harmless/likely to get used in LLVM once it's available? (I haven't looked at ranges in detail so I'm not sure if there's a clear cut-line & whether this falls on one side or the other) Like I could imagine a rule like "don't use anything from the <ranges> header or std::ranges namespace" which this ctor wouldn't fall afoul of.

https://github.com/llvm/llvm-project/pull/131832