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Empty slice fix #107316

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Merged
merged 5 commits into from
Sep 16, 2024
Merged

Empty slice fix #107316

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a175e2e
empty slice fix
michaelgsharp Sep 3, 2024
7c67f3f
PR comments and more testing
michaelgsharp Sep 5, 2024
a1a5318
fixing check
michaelgsharp Sep 5, 2024
4912e8f
fixing array rent init
michaelgsharp Sep 9, 2024
4e8fce0
fixes from PR comments
michaelgsharp Sep 16, 2024
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56 changes: 46 additions & 10 deletions ...braries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/ReadOnlyTensorSpan.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -655,34 +655,70 @@ public ReadOnlyTensorSpan<T> Slice(params scoped ReadOnlySpan<NRange> ranges)
if (ranges.Length != Lengths.Length)
throw new ArgumentOutOfRangeException(nameof(ranges), "Number of dimensions to slice does not equal the number of dimensions in the span");

ReadOnlyTensorSpan<T> toReturn;
scoped Span<nint> lengths;
scoped Span<nint> offsets;
nint[]? lengthsArray;
nint[]? offsetsArray;
if (Rank > TensorShape.MaxInlineRank)
{
lengths = stackalloc nint[Rank];
offsets = stackalloc nint[Rank];
lengthsArray = ArrayPool<nint>.Shared.Rent(Rank);
lengths = lengthsArray;
lengths = lengths.Slice(0, Rank);
lengthsArray = null;

offsetsArray = ArrayPool<nint>.Shared.Rent(Rank);
offsets = offsetsArray;
offsets = offsets.Slice(0, Rank);
offsetsArray = null;
}
else
{
lengths = new nint[Rank];
offsets = new nint[Rank];
lengths = stackalloc nint[Rank];
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not something to fix in this PR, but dynamically lengthed stackalloc is "bad"

Rather we should be using MaxInlineRank and slicing down to Rank

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Sounds good. Why is dynamically lengthed stackalloc bad?

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@tannergooding tannergooding Sep 16, 2024 •
edited
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Because it results in a lot of additional codegen to handle the fact the length is "unknown". Since we know the maximum is small, its better to do that and slice to avoid the pessimization.

Otherwise, it typically ends up cheaper to just use the array pool; rather than stackalloc at all.

offsets = stackalloc nint[Rank];

lengthsArray = null;
offsetsArray = null;
}

for (int i = 0; i < ranges.Length; i++)
{
(offsets[i], lengths[i]) = ranges[i].GetOffsetAndLength(Lengths[i]);
}

nint index = 0;
for (int i = 0; i < offsets.Length; i++)
// When we have an empty Tensor and someone wants to slice all of it, we should return an empty Tensor.
if (TensorSpanHelpers.CalculateTotalLength(Lengths) == 0)
{
index += Strides[i] * (offsets[i]);
for (int i = 0; i < offsets.Length; i++)
{
if (offsets[i] != 0 || lengths[i] != 0)
ThrowHelper.ThrowIndexOutOfRangeException();
}
toReturn = new ReadOnlyTensorSpan<T>(ref _reference, lengths, _shape.Strides, _shape._memoryLength);
}
else
{
nint index = 0;
for (int i = 0; i < offsets.Length; i++)
{
if (offsets[i] < 0 || offsets[i] >= Lengths[i])
ThrowHelper.ThrowIndexOutOfRangeException();

index += Strides[i] * (offsets[i]);
}

if (index >= _shape._memoryLength || index < 0)
ThrowHelper.ThrowIndexOutOfRangeException();

toReturn = new ReadOnlyTensorSpan<T>(ref Unsafe.Add(ref _reference, index), lengths, _shape.Strides, _shape._memoryLength - index);
}

if (index >= _shape._memoryLength || index < 0)
ThrowHelper.ThrowIndexOutOfRangeException();
if (offsetsArray != null)
ArrayPool<nint>.Shared.Return(offsetsArray);
if (lengthsArray != null)
ArrayPool<nint>.Shared.Return(lengthsArray);

return new ReadOnlyTensorSpan<T>(ref Unsafe.Add(ref _reference, index), lengths, _shape.Strides, _shape._memoryLength - index);
return toReturn;
}

/// <summary>
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55 changes: 44 additions & 11 deletions src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorSpan.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -690,37 +690,70 @@ public TensorSpan<T> Slice(params scoped ReadOnlySpan<NRange> ranges)
if (ranges.Length != Lengths.Length)
ThrowHelper.ThrowIndexOutOfRangeException();

TensorSpan<T> toReturn;
scoped Span<nint> lengths;
scoped Span<nint> offsets;
nint[]? lengthsArray;
nint[]? offsetsArray;
if (Rank > TensorShape.MaxInlineRank)
{
lengths = stackalloc nint[Rank];
offsets = stackalloc nint[Rank];
lengthsArray = ArrayPool<nint>.Shared.Rent(Rank);
lengths = lengthsArray;
lengths = lengths.Slice(0, Rank);
lengthsArray = null;

offsetsArray = ArrayPool<nint>.Shared.Rent(Rank);
offsets = offsetsArray;
offsets = offsets.Slice(0, Rank);
offsetsArray = null;
}
else
{
lengths = new nint[Rank];
offsets = new nint[Rank];
lengths = stackalloc nint[Rank];
offsets = stackalloc nint[Rank];

lengthsArray = null;
offsetsArray = null;
}

for (int i = 0; i < ranges.Length; i++)
{
(offsets[i], lengths[i]) = ranges[i].GetOffsetAndLength(Lengths[i]);
}

nint index = 0;
for (int i = 0; i < offsets.Length; i++)
// When we have an empty Tensor and someone wants to slice all of it, we should return an empty Tensor.
if (TensorSpanHelpers.CalculateTotalLength(Lengths) == 0)
{
if (offsets[i] < 0 || offsets[i] >= Lengths[i])
for (int i = 0; i < offsets.Length; i++)
{
if (offsets[i] != 0 || lengths[i] != 0)
ThrowHelper.ThrowIndexOutOfRangeException();
}
toReturn = new TensorSpan<T>(ref _reference, lengths, _shape.Strides, _shape._memoryLength);
}
else
{
nint index = 0;
for (int i = 0; i < offsets.Length; i++)
{
if (offsets[i] < 0 || offsets[i] >= Lengths[i])
ThrowHelper.ThrowIndexOutOfRangeException();

index += Strides[i] * (offsets[i]);
}

if (index >= _shape._memoryLength || index < 0)
ThrowHelper.ThrowIndexOutOfRangeException();

index += Strides[i] * (offsets[i]);
toReturn = new TensorSpan<T>(ref Unsafe.Add(ref _reference, index), lengths, _shape.Strides, _shape._memoryLength - index);
}

if (index >= _shape._memoryLength || index < 0)
ThrowHelper.ThrowIndexOutOfRangeException();
if (offsetsArray != null)
ArrayPool<nint>.Shared.Return(offsetsArray);
if (lengthsArray != null)
ArrayPool<nint>.Shared.Return(lengthsArray);

return new TensorSpan<T>(ref Unsafe.Add(ref _reference, index), lengths, _shape.Strides, _shape._memoryLength - index);
return toReturn;
}

/// <summary>
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3 changes: 3 additions & 0 deletions src/libraries/System.Numerics.Tensors/tests/ReadOnlyTensorSpanTests.cs
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Expand Up @@ -979,6 +979,9 @@ public static void ReadOnlyTensorSpanTryCopyTest()
[Fact]
public static void ReadOnlyTensorSpanSliceTest()
{
// Make sure slicing an empty TensorSpan works
new TensorSpan<double>(Array.Empty<double>()).Slice(new NRange[] { .. });

int[] a = [1, 2, 3, 4, 5, 6, 7, 8, 9];
int[] results = new int[9];
ReadOnlyTensorSpan<int> spanInt = a.AsTensorSpan(3, 3);
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3 changes: 3 additions & 0 deletions src/libraries/System.Numerics.Tensors/tests/TensorSpanTests.cs
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Expand Up @@ -1704,6 +1704,9 @@ public static void TensorSpanTryCopyTest()
[Fact]
public static void TensorSpanSliceTest()
{
// Make sure slicing an empty TensorSpan works
new TensorSpan<double>(Array.Empty<double>()).Slice(new NRange[] { .. });

int[] a = [1, 2, 3, 4, 5, 6, 7, 8, 9];
int[] results = new int[9];
TensorSpan<int> spanInt = a.AsTensorSpan(3, 3);
Expand Down
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