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Block inlining of IntroSort#89310

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Merged
AndyAyersMS merged 2 commits into from
Jul 21, 2023
Merged

Block inlining of IntroSort #89310

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Block inlining of IntroSort
AndyAyersMS Jul 21, 2023
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AndyAyersMS Jul 21, 2023
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6 changes: 6 additions & 0 deletions src/libraries/System.Private.CoreLib/src/System/Array.cs
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Original file line numberDiff line numberDiff line change
Expand Up@@ -2207,6 +2207,9 @@ private void IntrospectiveSort(int left, int length)
}
}

// IntroSort is recursive; block it from being inlined into itself as
// this is currenly not profitable.
[MethodImpl(MethodImplOptions.NoInlining)]

@stephentoubstephentoubJul 21, 2023

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Can we include a comment as to why this is here? I imagine the calculus around whether this is valuable could change in the future.

@AndyAyersMSAndyAyersMSJul 21, 2023

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Added.

Note IntroSort is nominally doubly recursive but has already had the tail recursive call transformed into a loop manually. If we were ever tempted to undo that and rely on the JIT to do something similar, we might find the NoInline annotation would inhibit that transformation too.

@EgorBo we might consider special heuristics for recursion, generally if the method is large and doesn't have a frequent fast path that avoids recursion, then there's not much to be gained.

private void IntroSort(int lo, int hi, int depthLimit)
{
Debug.Assert(hi >= lo);
Expand DownExpand Up@@ -2421,6 +2424,9 @@ private void IntrospectiveSort(int left, int length)
}
}

// IntroSort is recursive; block it from being inlined into itself as
// this is currenly not profitable.
[MethodImpl(MethodImplOptions.NoInlining)]
private void IntroSort(int lo, int hi, int depthLimit)
{
Debug.Assert(hi >= lo);
Expand Down
6 changes: 6 additions & 0 deletions src/libraries/System.Private.CoreLib/src/System/Collections/Generic/ArraySortHelper.cs
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Original file line numberDiff line numberDiff line change
Expand Up@@ -128,6 +128,9 @@ internal static void IntrospectiveSort(Span<T> keys, Comparison<T> comparer)
}
}

// IntroSort is recursive; block it from being inlined into itself as
// this is currenly not profitable.
[MethodImpl(MethodImplOptions.NoInlining)]
private static void IntroSort(Span<T> keys, int depthLimit, Comparison<T> comparer)
{
Debug.Assert(!keys.IsEmpty);
Expand DownExpand Up@@ -402,6 +405,9 @@ private static void Swap(ref T i, ref T j)
j = t;
}

// IntroSort is recursive; block it from being inlined into itself as
// this is currenly not profitable.
[MethodImpl(MethodImplOptions.NoInlining)]
private static void IntroSort(Span<T> keys, int depthLimit)
{
Debug.Assert(!keys.IsEmpty);
Expand Down