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Use a simple temp instead of InlineArray1 #73086

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May 8, 2024
Merged

Use a simple temp instead of InlineArray1 #73086

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5ee9248
Use a simple temp instead of InlineArray1
RikkiGibson Apr 17, 2024
3e51b81
fix test failures
RikkiGibson Apr 18, 2024
60d90aa
fix tests
RikkiGibson Apr 18, 2024
9d69fa7
Pass isKnownToReferToTempIfReferenceType because the other place in t…
RikkiGibson Apr 19, 2024
754c7c4
Show that temps are not reused
RikkiGibson Apr 19, 2024
e9e7d2a
Undo unintentional change
RikkiGibson Apr 19, 2024
410ec68
Remove true argument for isKnownToReferToTempIfReferenceType
RikkiGibson Apr 26, 2024
35c2769
Address feedback
RikkiGibson Apr 26, 2024
8712cd2
Fix test
RikkiGibson Apr 26, 2024
1c459b3
fix test
RikkiGibson Apr 29, 2024
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17 changes: 17 additions & 0 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 @@ -439,6 +439,23 @@ private static bool ShouldUseInlineArray(BoundCollectionExpressionBase node, CSh
Debug.Assert(_compilation.Assembly.RuntimeSupportsInlineArrayTypes);

int arrayLength = elements.Length;
if (arrayLength == 1
&& _factory.WellKnownMember(asReadOnlySpan
? WellKnownMember.System_ReadOnlySpan_T__ctor_ref_readonly_T
: WellKnownMember.System_Span_T__ctor_ref_T, isOptional: true) is MethodSymbol spanRefConstructor)
{
// Special case: no need to create an InlineArray1 type. Just use a temp of the element type.
var spanType = _factory
.WellKnownType(asReadOnlySpan ? WellKnownType.System_ReadOnlySpan_T : WellKnownType.System_Span_T)
.Construct([elementType]);
var constructor = spanRefConstructor.AsMember(spanType);
var element = VisitExpression((BoundExpression)elements[0]);
var temp = _factory.StoreToTemp(element, out var assignment, isKnownToReferToTempIfReferenceType: true);
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@AlekseyTs AlekseyTs Apr 25, 2024 •
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isKnownToReferToTempIfReferenceType

  1. In general, when not sure, the safest value for this parameter is false. It enables some optimizations and you don't want to apply those when they are not appropriate because that can lead to an incorrect result, i.e. bugs.
  2. This value is meaningful only for ref locals. I would avoid setting it to true for non-ref locals.
  3. The meaning of this flag - this local refers to something (it is a ref), and if the type of that something is a reference type, there is a guarantee that that something is a temporary (not a user local, not a parameter, not a field, etc.) So, it is about what we are referring to with this local. Obviously the temp we are assigning to here is a temp, but this value is not about that.

So, I recommend, cleaning up this code and any other "collection expressions" code with respect to values used for this parameter. In order to avoid spreading questionable code through copy/paste and eventually hitting a scenario that can actually break because we haven't given much thought about the value. #Closed

locals.Add(temp.LocalSymbol);
var call = _factory.New(constructor, arguments: [temp], argumentRefKinds: [asReadOnlySpan ? RefKind.In : RefKind.Ref]);
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return _factory.Sequence([assignment], call);
}

var inlineArrayType = _factory.ModuleBuilderOpt.EnsureInlineArrayTypeExists(syntax, _factory, arrayLength, _diagnostics.DiagnosticBag).Construct(ImmutableArray.Create(elementType));
Debug.Assert(inlineArrayType.HasInlineArrayAttribute(out int inlineArrayLength) && inlineArrayLength == arrayLength);

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15 changes: 15 additions & 0 deletions src/Compilers/CSharp/Portable/Lowering/SyntheticBoundNodeFactory.cs
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Expand Up @@ -789,6 +789,21 @@ public BoundObjectCreationExpression New(NamedTypeSymbol type, ImmutableArray<Bo
public BoundObjectCreationExpression New(MethodSymbol ctor, ImmutableArray<BoundExpression> args)
=> new BoundObjectCreationExpression(Syntax, ctor, args) { WasCompilerGenerated = true };

public BoundObjectCreationExpression New(MethodSymbol constructor, ImmutableArray<BoundExpression> arguments, ImmutableArray<RefKind> argumentRefKinds)
=> new BoundObjectCreationExpression(
Syntax,
constructor,
arguments,
argumentNamesOpt: default,
argumentRefKinds,
expanded: false,
argsToParamsOpt: default,
defaultArguments: default,
constantValueOpt: null,
initializerExpressionOpt: null,
constructor.ContainingType)
{ WasCompilerGenerated = true };

public BoundObjectCreationExpression New(WellKnownMember wm, ImmutableArray<BoundExpression> args)
{
var ctor = WellKnownMethod(wm);
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1,613 changes: 788 additions & 825 deletions src/Compilers/CSharp/Test/Emit2/Semantics/CollectionExpressionTests.cs
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8 changes: 2 additions & 6 deletions src/Compilers/CSharp/Test/Emit2/Semantics/ParamsCollectionTests.cs
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Expand Up @@ -4558,9 +4558,7 @@ static void Test(params System.Span<int> a)

CompileAndVerify(
comp,
verify: ExecutionConditionUtil.IsMonoOrCoreClr ?
Verification.FailsILVerify with { ILVerifyMessage = "[InlineArrayAsSpan]: Return type is ByRef, TypedReference, ArgHandle, or ArgIterator. { Offset = 0xc }" }
: Verification.Skipped,
verify: Verification.Skipped,
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Curious now. Lets say I have the following code:

M(1);
M(2);
void M(params Span<int> i) { }

After this change the compiler will optimize the calling code to roughly be:

int tmp = 1;
M(new Span<int>(ref temp));

But do we create 1 or 2 temps here? Guessing we only create one today but want to check. This could be a significant optimization opportunity for us in the future.

expectedOutput: ExpectedOutput(@"
int
int")).VerifyDiagnostics();
Expand Down Expand Up @@ -4598,9 +4596,7 @@ class C3 : C2 {}

CompileAndVerify(
comp,
verify: ExecutionConditionUtil.IsMonoOrCoreClr ?
Verification.FailsILVerify with { ILVerifyMessage = "[InlineArrayAsSpan]: Return type is ByRef, TypedReference, ArgHandle, or ArgIterator. { Offset = 0xc }" }
: Verification.Skipped,
verify: Verification.Skipped,
expectedOutput: ExpectedOutput(@"
C2
C2")).VerifyDiagnostics();
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2 changes: 2 additions & 0 deletions src/Compilers/CSharp/Test/Symbol/Symbols/MissingSpecialMember.cs
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Expand Up @@ -1071,6 +1071,8 @@ public void AllWellKnownTypeMembers()
case WellKnownMember.System_Span_T__CopyTo_Span_T:
case WellKnownMember.System_ReadOnlySpan_T__CopyTo_Span_T:
case WellKnownMember.System_Collections_Immutable_ImmutableArray_T__AsSpan:
case WellKnownMember.System_Span_T__ctor_ref_T:
case WellKnownMember.System_ReadOnlySpan_T__ctor_ref_readonly_T:
// Not always available.
continue;
}
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2 changes: 2 additions & 0 deletions src/Compilers/Core/Portable/WellKnownMember.cs
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Expand Up @@ -479,13 +479,15 @@ internal enum WellKnownMember

System_Span_T__ctor_Pointer,
System_Span_T__ctor_Array,
System_Span_T__ctor_ref_T,
System_Span_T__get_Item,
System_Span_T__get_Length,
System_Span_T__Slice_Int_Int,

System_ReadOnlySpan_T__ctor_Pointer,
System_ReadOnlySpan_T__ctor_Array,
System_ReadOnlySpan_T__ctor_Array_Start_Length,
System_ReadOnlySpan_T__ctor_ref_readonly_T,
System_ReadOnlySpan_T__get_Item,
System_ReadOnlySpan_T__get_Length,
System_ReadOnlySpan_T__Slice_Int_Int,
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18 changes: 18 additions & 0 deletions src/Compilers/Core/Portable/WellKnownMembers.cs
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Expand Up @@ -3333,6 +3333,14 @@ static WellKnownMembers()
1, // Method Signature
(byte)SignatureTypeCode.TypeHandle, (byte)SpecialType.System_Void, // Return Type
(byte)SignatureTypeCode.SZArray, (byte)SignatureTypeCode.GenericTypeParameter, 0,

// System_Span_T__ctor_ref_T
(byte)(MemberFlags.Constructor), // Flags
(byte)WellKnownType.ExtSentinel, (byte)(WellKnownType.System_Span_T - WellKnownType.ExtSentinel), // DeclaringTypeId
0, // Arity
1, // Method Signature
(byte)SignatureTypeCode.TypeHandle, (byte)SpecialType.System_Void, // Return Type
(byte)SignatureTypeCode.ByReference, (byte)SignatureTypeCode.GenericTypeParameter, 0,

// System_Span_T__get_Item
(byte)(MemberFlags.PropertyGet), // Flags
Expand Down Expand Up @@ -3388,6 +3396,14 @@ static WellKnownMembers()
(byte)SignatureTypeCode.TypeHandle, (byte)SpecialType.System_Int32,
(byte)SignatureTypeCode.TypeHandle, (byte)SpecialType.System_Int32,

// System_ReadOnlySpan_T__ctor_ref_readonly_T
(byte)(MemberFlags.Constructor), // Flags
(byte)WellKnownType.ExtSentinel, (byte)(WellKnownType.System_ReadOnlySpan_T - WellKnownType.ExtSentinel), // DeclaringTypeId
0, // Arity
1, // Method Signature
(byte)SignatureTypeCode.TypeHandle, (byte)SpecialType.System_Void, // Return Type
(byte)SignatureTypeCode.ByReference, (byte)SignatureTypeCode.GenericTypeParameter, 0,
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The signature of the ReadOnlySpan consructor changed between net7.0 and net8.0 from in to ref readonly. Will this match both versions?

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In practice I expect it will. This is because the comparison here is just checking that it is a managed reference according to the runtime. It doesn't check anything about the readability or writability of the reference (C#-level concepts).

However for the particular way this optimization is implemented, I think won't even enter the path for using the 'Span referencing a temp' optimization for net7, because the containing code path is gated on InlineArray runtime feature availability, IIRC. This is shown in the codegen for the tests which use target framework net7.

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Yep. I'm less interested in the optimization being applied and more interested in making sure that this well known member can see both variations of the signature. Otherwise it could create confusion for later changes.


// System_ReadOnlySpan_T__get_Item
(byte)(MemberFlags.PropertyGet), // Flags
(byte)WellKnownType.ExtSentinel, (byte)(WellKnownType.System_ReadOnlySpan_T - WellKnownType.ExtSentinel), // DeclaringTypeId
Expand Down Expand Up @@ -4722,12 +4738,14 @@ static WellKnownMembers()
".ctor", // System_Runtime_CompilerServices_ObsoleteAttribute__ctor
".ctor", // System_Span_T__ctor_Pointer
".ctor", // System_Span_T__ctor_Array
".ctor", // System_Span_T__ctor_ref_T
"get_Item", // System_Span_T__get_Item
"get_Length", // System_Span_T__get_Length
"Slice", // System_Span_T__Slice_Int_Int
".ctor", // System_ReadOnlySpan_T__ctor_Pointer
".ctor", // System_ReadOnlySpan_T__ctor_Array
".ctor", // System_ReadOnlySpan_T__ctor_Array_Start_Length
".ctor", // System_ReadOnlySpan_T__ctor_ref_readonly_T
"get_Item", // System_ReadOnlySpan_T__get_Item
"get_Length", // System_ReadOnlySpan_T__get_Length
"Slice", // System_ReadOnlySpan_T__Slice_Int_Int
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8 changes: 6 additions & 2 deletions src/Compilers/VisualBasic/Test/Symbol/SymbolsTests/WellKnownTypeValidationTests.vb
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Expand Up @@ -821,7 +821,9 @@ End Namespace
WellKnownMember.System_ReadOnlySpan_T__ToArray,
WellKnownMember.System_Span_T__CopyTo_Span_T,
WellKnownMember.System_ReadOnlySpan_T__CopyTo_Span_T,
WellKnownMember.System_Collections_Immutable_ImmutableArray_T__AsSpan
WellKnownMember.System_Collections_Immutable_ImmutableArray_T__AsSpan,
WellKnownMember.System_Span_T__ctor_ref_T,
WellKnownMember.System_ReadOnlySpan_T__ctor_ref_readonly_T
' Not always available.
Continue For
End Select
Expand Down Expand Up @@ -1026,7 +1028,9 @@ End Namespace
WellKnownMember.System_ReadOnlySpan_T__ToArray,
WellKnownMember.System_Span_T__CopyTo_Span_T,
WellKnownMember.System_ReadOnlySpan_T__CopyTo_Span_T,
WellKnownMember.System_Collections_Immutable_ImmutableArray_T__AsSpan
WellKnownMember.System_Collections_Immutable_ImmutableArray_T__AsSpan,
WellKnownMember.System_Span_T__ctor_ref_T,
WellKnownMember.System_ReadOnlySpan_T__ctor_ref_readonly_T
' Not always available.
Continue For
End Select
Expand Down