IDE0057: Slice can be simplified

[msedi]

Some C# analyzer tells me that this line can be optimized:

new Vector<T>(B.Slice(Idx))

IDE0057: Slice can be simplified to this

new Vector<T>(B[Idx..])

What is the benefit only less text. I would think a range is created here that slows down performance?

[YairHalberstadt]

What is the benefit only less text.

Correct, although I would argue it's more that's it's more declarative than less text. I don't know what the parameters to slice are. Length? Start? Finish? But ranges are a well known construct.

I would think a range is created here that slows down performance?

The runtime team works very hard to make sure that isn't the case. They definitely will treat it as a bug if the Jit output is worse.

[svick]

@YairHalberstadt The output is a bit worse, at least based on what I see on SharpLab.

[msedi]

@svick: Should I file it as an issue?

[YairHalberstadt]

@msedi yes

[YairHalberstadt]

@svick make sure you're checking .Net 5, not X64 which is .net core 3.1

[BreyerW]

Also non-span based range should be considerably worse than span. But thats unfixable, net 5 even introduced an analyzer to warn on non-span based range which is annoying but c'est la vie (normally non-span based range should behave like span-based but due to limits that isnt the case)

[CyrusNajmabadi]

There's no issue here with the analyzer fwiw. The analyzer is just telling you can simplify things in this manner if you so choose.

If the jitted code is suboptimal, you can certainly open an issue on that.

[msedi]

See dotnet/roslyn#47626