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Prefer converting to ReadOnlySpan for spread optimization when we do not need to write #71733

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merged 3 commits into from
Jan 25, 2024
Merged

Prefer converting to ReadOnlySpan for spread optimization when we do not need to write #71733

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Prefer converting to ReadOnlySpan for spread optimizatio when we do n…
RikkiGibson Jan 19, 2024
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Prefer Verifier.VerifyDiagnostics
RikkiGibson Jan 25, 2024
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34 changes: 18 additions & 16 deletions src/Compilers/CSharp/Portable/Lowering/LocalRewriter/LocalRewriter_CollectionExpression.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -538,11 +538,11 @@ private BoundExpression CreateAndPopulateArray(BoundCollectionExpression node, A
return _factory.Call(rewrittenSpreadExpression, listToArrayMethod.AsMember((NamedTypeSymbol)spreadExpression.Type!));
}

if (TryGetSpanConversion(spreadExpression.Type, out var asSpanMethod))
if (TryGetSpanConversion(spreadExpression.Type, writableOnly: false, out var asSpanMethod))
{
var spanType = CallAsSpanMethod(spreadExpression, asSpanMethod).Type!.OriginalDefinition;
if (tryGetToArrayMethod(spanType, WellKnownType.System_Span_T, WellKnownMember.System_Span_T__ToArray, out var toArrayMethod)
|| tryGetToArrayMethod(spanType, WellKnownType.System_ReadOnlySpan_T, WellKnownMember.System_ReadOnlySpan_T__ToArray, out toArrayMethod))
if (tryGetToArrayMethod(spanType, WellKnownType.System_ReadOnlySpan_T, WellKnownMember.System_ReadOnlySpan_T__ToArray, out var toArrayMethod)
|| tryGetToArrayMethod(spanType, WellKnownType.System_Span_T, WellKnownMember.System_Span_T__ToArray, out toArrayMethod))
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Reordered these as I think the ReadOnlySpan case will now be more common

{
var rewrittenSpreadExpression = CallAsSpanMethod(VisitExpression(spreadExpression), asSpanMethod);
return _factory.Call(rewrittenSpreadExpression, toArrayMethod.AsMember((NamedTypeSymbol)rewrittenSpreadExpression.Type!));
Expand Down Expand Up @@ -649,7 +649,7 @@ bool tryGetToArrayMethod(TypeSymbol spreadTypeOriginalDefinition, WellKnownType

// https://github.com/dotnet/roslyn/issues/71270
// Could save the targetSpan to temp in the enclosing scope, but need to make sure we are async-safe etc.
if (!TryConvertToSpanOrReadOnlySpan(arrayTemp, out var targetSpan))
if (!TryConvertToSpan(arrayTemp, writableOnly: true, out var targetSpan))
return false;

PerformCopyToOptimization(sideEffects, localsBuilder, indexTemp, targetSpan, rewrittenSpreadOperand, spanSliceMethod, spreadElementAsSpan, getLengthMethod, copyToMethod);
Expand All @@ -667,15 +667,16 @@ bool tryGetToArrayMethod(TypeSymbol spreadTypeOriginalDefinition, WellKnownType
arrayType);
}

/// <summary>
/// Returns true if type is convertible to Span or ReadOnlySpan.
/// If non-identity conversion, also returns a non-null asSpanMethod.
/// </summary>
/// <returns>
/// If <paramref name="writableOnly"/> is <see langword="true"/>, will only return true with a conversion to writable Span.
/// Otherwise, will return a conversion directly to ReadOnlySpan if one is known, and may return a conversion to Span if no direct conversion to ReadOnlySpan is known, or if the type is already a Span.
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/// If non-identity conversion, also returns a non-null <paramref name="asSpanMethod"/>.
/// </returns>
/// <remarks>We are assuming that the well-known types we are converting to/from do not have constraints on their type parameters.</remarks>
private bool TryGetSpanConversion(TypeSymbol type, out MethodSymbol? asSpanMethod)
private bool TryGetSpanConversion(TypeSymbol type, bool writableOnly, out MethodSymbol? asSpanMethod)
{
if (type is ArrayTypeSymbol { IsSZArray: true } arrayType
&& _factory.WellKnownMethod(WellKnownMember.System_Span_T__ctor_Array, isOptional: true) is { } spanCtorArray)
&& _factory.WellKnownMethod(writableOnly ? WellKnownMember.System_Span_T__ctor_Array : WellKnownMember.System_ReadOnlySpan_T__ctor_Array, isOptional: true) is { } spanCtorArray)
{
// conversion to 'object' will fail if, for example, 'arrayType.ElementType' is a pointer.
var useSiteInfo = CompoundUseSiteInfo<AssemblySymbol>.Discarded;
Expand All @@ -692,14 +693,15 @@ private bool TryGetSpanConversion(TypeSymbol type, out MethodSymbol? asSpanMetho
return false;
}

if (namedType.OriginalDefinition.Equals(_compilation.GetWellKnownType(WellKnownType.System_Span_T), TypeCompareKind.ConsiderEverything)
|| namedType.OriginalDefinition.Equals(_compilation.GetWellKnownType(WellKnownType.System_ReadOnlySpan_T), TypeCompareKind.ConsiderEverything))
if ((!writableOnly && namedType.OriginalDefinition.Equals(_compilation.GetWellKnownType(WellKnownType.System_ReadOnlySpan_T), TypeCompareKind.ConsiderEverything))
|| namedType.OriginalDefinition.Equals(_compilation.GetWellKnownType(WellKnownType.System_Span_T), TypeCompareKind.ConsiderEverything))
{
asSpanMethod = null;
return true;
}

if (namedType.OriginalDefinition.Equals(_compilation.GetWellKnownType(WellKnownType.System_Collections_Immutable_ImmutableArray_T), TypeCompareKind.ConsiderEverything)
if (!writableOnly
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&& namedType.OriginalDefinition.Equals(_compilation.GetWellKnownType(WellKnownType.System_Collections_Immutable_ImmutableArray_T), TypeCompareKind.ConsiderEverything)
&& _factory.WellKnownMethod(WellKnownMember.System_Collections_Immutable_ImmutableArray_T__AsSpan, isOptional: true) is { } immutableArrayAsSpanMethod)
{
asSpanMethod = immutableArrayAsSpanMethod.AsMember(namedType);
Expand All @@ -717,12 +719,12 @@ private bool TryGetSpanConversion(TypeSymbol type, out MethodSymbol? asSpanMetho
return false;
}

private bool TryConvertToSpanOrReadOnlySpan(BoundExpression expression, [NotNullWhen(true)] out BoundExpression? span)
private bool TryConvertToSpan(BoundExpression expression, bool writableOnly, [NotNullWhen(true)] out BoundExpression? span)
{
var type = expression.Type;
Debug.Assert(type is not null);

if (!TryGetSpanConversion(type, out var asSpanMethod))
if (!TryGetSpanConversion(type, writableOnly, out var asSpanMethod))
{
span = null;
return false;
Expand Down Expand Up @@ -768,7 +770,7 @@ private BoundExpression CallAsSpanMethod(BoundExpression spreadExpression, Metho
if (_factory.WellKnownMethod(WellKnownMember.System_Span_T__Slice_Int_Int, isOptional: true) is not { } spanSliceMethod)
return null;

if (!TryConvertToSpanOrReadOnlySpan(rewrittenSpreadOperand, out var spreadOperandAsSpan))
if (!TryConvertToSpan(rewrittenSpreadOperand, writableOnly: false, out var spreadOperandAsSpan))
return null;

if ((getSpanMethodsForSpread(WellKnownType.System_ReadOnlySpan_T, WellKnownMember.System_ReadOnlySpan_T__get_Length, WellKnownMember.System_ReadOnlySpan_T__CopyTo_Span_T)
Expand Down
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