Use safe Span.Slice loop pattern in Enumerable.FillIncrementing

[EgorBo]

Note

This PR was authored with assistance from GitHub Copilot (AI-generated content).

Rewrites the vectorized fill in Enumerable.FillIncrementing<T> to use the safe while (span.Length >= CONST) { ...; span = span.Slice(CONST); } loop pattern, removing all Unsafe.* / MemoryMarshal.GetReference plumbing. JIT recognizes this shape and elides the bounds checks.

Codegen

Small diffs, no new checks. No perf impact.

[EgorBo]

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[Copilot]

Pull request overview

Refactors Enumerable.FillIncrementing<T> to use a safe Span<T>.Slice-driven loop shape for the vectorized fill, eliminating Unsafe/MemoryMarshal usage while keeping JIT-friendly bounds-check elimination.

Changes:

• Removed Unsafe.* / MemoryMarshal.GetReference pointer-walking in FillIncrementing<T>.
• Replaced vector stores with Vector<T>.CopyTo(destination) inside a while (destination.Length >= Vector<T>.Count) loop and advanced via destination = destination.Slice(...).
• Simplified the scalar tail fill to iterate directly over the remaining span.

[EgorBo]

@EgorBot -intel -arm

using System.Linq;
using BenchmarkDotNet.Attributes;

public class RangeToArrayBench
{
    [Params(0, 1, 4, 8, 16, 64, 256, 1024, 16384, 1_000_000)]
    public int Count;

    [Benchmark]
    public int[] RangeToArray() => Enumerable.Range(0, Count).ToArray();
}