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Use safe Span.Slice loop pattern in Enumerable.MinMaxInteger #127428

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Use safe Span.Slice loop pattern in Enumerable.MinMaxInteger #127428

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39c54e1
Use safe Span.Slice loop pattern in Enumerable.MinMaxInteger
EgorBo Apr 25, 2026
c1847b0
Fix tail-load bounds bug for spans of exactly one vector
EgorBo Apr 25, 2026
209c58a
Merge branch 'main' into copilot/safe-loop-maxmin
EgorBo Apr 26, 2026
7d105bd
Merge branch 'main' of https://github.com/dotnet/runtime into copilot…
EgorBo Apr 26, 2026
1b56dc8
mark types as intrinsic
EgorBo Apr 26, 2026
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49 changes: 23 additions & 26 deletions src/libraries/System.Linq/src/System/Linq/MaxMin.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,8 +3,6 @@

using System.Collections.Generic;
using System.Numerics;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Runtime.Intrinsics;

namespace System.Linq
Expand Down Expand Up @@ -50,18 +48,19 @@ private static T MinMaxInteger<T, TMinMax>(this IEnumerable<T> source)
}
else if (!Vector256.IsHardwareAccelerated || !Vector256<T>.IsSupported || span.Length < Vector256<T>.Count)
{
ref T current = ref MemoryMarshal.GetReference(span);
ref T lastVectorStart = ref Unsafe.Add(ref current, span.Length - Vector128<T>.Count);
// Capture the trailing overlapping vector before slicing, so it remains valid
// even when span.Length == Vector128<T>.Count (in which case it equals the first vector).
ReadOnlySpan<T> lastVec = span.Slice(span.Length - Vector128<T>.Count);

Vector128<T> best = Vector128.LoadUnsafe(ref current);
current = ref Unsafe.Add(ref current, Vector128<T>.Count);
Vector128<T> best = Vector128.Create(span);
span = span.Slice(Vector128<T>.Count);

while (Unsafe.IsAddressLessThan(ref current, ref lastVectorStart))
while (span.Length >= Vector128<T>.Count)
{
best = TMinMax.Compare(best, Vector128.LoadUnsafe(ref current));
current = ref Unsafe.Add(ref current, Vector128<T>.Count);
best = TMinMax.Compare(best, Vector128.Create(span));
span = span.Slice(Vector128<T>.Count);
}
best = TMinMax.Compare(best, Vector128.LoadUnsafe(ref lastVectorStart));
best = TMinMax.Compare(best, Vector128.Create(lastVec));
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value = best[0];
for (int i = 1; i < Vector128<T>.Count; i++)
Expand All @@ -74,18 +73,17 @@ private static T MinMaxInteger<T, TMinMax>(this IEnumerable<T> source)
}
else if (!Vector512.IsHardwareAccelerated || !Vector512<T>.IsSupported || span.Length < Vector512<T>.Count)
{
ref T current = ref MemoryMarshal.GetReference(span);
ref T lastVectorStart = ref Unsafe.Add(ref current, span.Length - Vector256<T>.Count);
ReadOnlySpan<T> lastVec = span.Slice(span.Length - Vector256<T>.Count);

Vector256<T> best = Vector256.LoadUnsafe(ref current);
current = ref Unsafe.Add(ref current, Vector256<T>.Count);
Vector256<T> best = Vector256.Create(span);
span = span.Slice(Vector256<T>.Count);

while (Unsafe.IsAddressLessThan(ref current, ref lastVectorStart))
while (span.Length >= Vector256<T>.Count)
{
best = TMinMax.Compare(best, Vector256.LoadUnsafe(ref current));
current = ref Unsafe.Add(ref current, Vector256<T>.Count);
best = TMinMax.Compare(best, Vector256.Create(span));
span = span.Slice(Vector256<T>.Count);
}
best = TMinMax.Compare(best, Vector256.LoadUnsafe(ref lastVectorStart));
best = TMinMax.Compare(best, Vector256.Create(lastVec));
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value = best[0];
for (int i = 1; i < Vector256<T>.Count; i++)
Expand All @@ -98,18 +96,17 @@ private static T MinMaxInteger<T, TMinMax>(this IEnumerable<T> source)
}
else
{
ref T current = ref MemoryMarshal.GetReference(span);
ref T lastVectorStart = ref Unsafe.Add(ref current, span.Length - Vector512<T>.Count);
ReadOnlySpan<T> lastVec = span.Slice(span.Length - Vector512<T>.Count);

Vector512<T> best = Vector512.LoadUnsafe(ref current);
current = ref Unsafe.Add(ref current, Vector512<T>.Count);
Vector512<T> best = Vector512.Create(span);
span = span.Slice(Vector512<T>.Count);

while (Unsafe.IsAddressLessThan(ref current, ref lastVectorStart))
while (span.Length >= Vector512<T>.Count)
{
best = TMinMax.Compare(best, Vector512.LoadUnsafe(ref current));
current = ref Unsafe.Add(ref current, Vector512<T>.Count);
best = TMinMax.Compare(best, Vector512.Create(span));
span = span.Slice(Vector512<T>.Count);
}
best = TMinMax.Compare(best, Vector512.LoadUnsafe(ref lastVectorStart));
best = TMinMax.Compare(best, Vector512.Create(lastVec));
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value = best[0];
for (int i = 1; i < Vector512<T>.Count; i++)
Expand Down
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