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Avoid allocations in CanWrap... methods #3711

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merged 4 commits into from
Oct 18, 2023
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Avoid allocations in CanWrap... methods #3711

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16c310e
Avoid allocations in CanWrap... methods
martin-strecker-sonarsource Oct 16, 2023
b5fd4b5
Remove local function
martin-strecker-sonarsource Oct 17, 2023
3386603
Revert changes for static delegate
martin-strecker-sonarsource Oct 17, 2023
12b6f93
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martin-strecker-sonarsource Oct 17, 2023
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36 changes: 15 additions & 21 deletions StyleCop.Analyzers/StyleCop.Analyzers/Lightup/LightupHelpers.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -65,15 +65,13 @@ internal static bool CanWrapObject(object obj, Type underlyingType)
return false;
}

ConcurrentDictionary<Type, bool> wrappedObject = SupportedObjectWrappers.GetOrAdd(underlyingType, _ => new ConcurrentDictionary<Type, bool>());
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Was there an actual problem with this first lookup (in each method)? I haven't dug into your IL comparison, but since no capture is needed, it seems the only possible overhead would be creating the func instance. I think I recall that lambdas are automatically detected to be static if possible, but in case that is not correct, wouldn't simply marking the lambda as static be the best change?

ConcurrentDictionary<Type, bool> wrappedObject = SupportedObjectWrappers.GetOrAdd(underlyingType, static _ => new ConcurrentDictionary<Type, bool>());

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The IL confirmed that the delegate instance is indeed cached between calls in a static field:

// Load the delegate instance from a static field  
    IL_0033: ldsfld       class System.Func`2<System.Type, ConcurrentDictionary`2<SyntaxKind, bool>> StyleCop.Analyzers.Lightup.LightupHelpers/'<>c'::'<>9__30_0'
    IL_0038: dup
// Branch if not null?
    IL_0039: brtrue.s     IL_0052
    IL_003b: pop
// ..
// Create the delegate
    IL_0047: newobj       instance void class System.Func`2<System.Type, ConcurrentDictionary`2<SyntaxKind, bool>>::.ctor(object, native int)
    IL_004c: dup
// Store it
    IL_004d: stsfld       class System.Func`2<System.Type, ConcurrentDictionary`2<SyntaxKind, bool>> StyleCop.Analyzers.Lightup.LightupHelpers/'<>c'::'<>9__30_0'
// Invoke the delegate
    IL_0052: callvirt     instance !1/*class [System.Collections.Concurrent]System.Collections.Concurrent.ConcurrentDictionary`2<valuetype [Microsoft.CodeAnalysis.CSharp]Microsoft.CodeAnalysis.CSharp.SyntaxKind, bool>*/ class [System.Collections.Concurrent]System.Collections.Concurrent.ConcurrentDictionary`2<class [System.Runtime]System.Type, class [System.Collections.Concurrent]System.Collections.Concurrent.ConcurrentDictionary`2<valuetype [Microsoft.CodeAnalysis.CSharp]Microsoft.CodeAnalysis.CSharp.SyntaxKind, bool>>::GetOrAdd(!0/*class [System.Runtime]System.Type*/, class [System.Runtime]System.Func`2<!0/*class [System.Runtime]System.Type*/, !1/*class [System.Collections.Concurrent]System.Collections.Concurrent.ConcurrentDictionary`2<valuetype [Microsoft.CodeAnalysis.CSharp]Microsoft.CodeAnalysis.CSharp.SyntaxKind, bool>*/>)

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📝 This line does not need to change.

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I just kept the static to emphasize the non-capturing semantic of the lambda.

ConcurrentDictionary<Type, bool> wrappedObject = SupportedObjectWrappers.GetOrAdd(underlyingType, static _ => new ConcurrentDictionary<Type, bool>());

// Avoid creating the delegate if the value already exists
bool canCast;
if (!wrappedObject.TryGetValue(obj.GetType(), out canCast))
// Avoid creating a delegate and capture class
if (!wrappedObject.TryGetValue(obj.GetType(), out var canCast))
{
canCast = wrappedObject.GetOrAdd(
obj.GetType(),
kind => underlyingType.GetTypeInfo().IsAssignableFrom(obj.GetType().GetTypeInfo()));
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📝 This line is the source of the capturing allocation (specifically, capturing a method parameter in a lambda forces the the capture to be allocated on all paths and not just the one that creates this delegate).

canCast = underlyingType.GetTypeInfo().IsAssignableFrom(obj.GetType().GetTypeInfo());
wrappedObject.TryAdd(obj.GetType(), canCast);
Comment on lines +73 to +74
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❗ Requesting that this pull request be reduced to just this two line change in each case.

}

return canCast;
Expand All @@ -93,15 +91,13 @@ internal static bool CanWrapNode(SyntaxNode node, Type underlyingType)
return false;
}

ConcurrentDictionary<SyntaxKind, bool> wrappedSyntax = SupportedSyntaxWrappers.GetOrAdd(underlyingType, _ => new ConcurrentDictionary<SyntaxKind, bool>());
ConcurrentDictionary<SyntaxKind, bool> wrappedSyntax = SupportedSyntaxWrappers.GetOrAdd(underlyingType, static _ => new ConcurrentDictionary<SyntaxKind, bool>());

// Avoid creating the delegate if the value already exists
bool canCast;
if (!wrappedSyntax.TryGetValue(node.Kind(), out canCast))
// Avoid creating a delegate and capture class
if (!wrappedSyntax.TryGetValue(node.Kind(), out var canCast))
{
canCast = wrappedSyntax.GetOrAdd(
node.Kind(),
kind => underlyingType.GetTypeInfo().IsAssignableFrom(node.GetType().GetTypeInfo()));
canCast = underlyingType.GetTypeInfo().IsAssignableFrom(node.GetType().GetTypeInfo());
wrappedSyntax.TryAdd(node.Kind(), canCast);
}

return canCast;
Expand All @@ -121,15 +117,13 @@ internal static bool CanWrapOperation(IOperation operation, Type underlyingType)
return false;
}

ConcurrentDictionary<OperationKind, bool> wrappedSyntax = SupportedOperationWrappers.GetOrAdd(underlyingType, _ => new ConcurrentDictionary<OperationKind, bool>());
ConcurrentDictionary<OperationKind, bool> wrappedSyntax = SupportedOperationWrappers.GetOrAdd(underlyingType, static _ => new ConcurrentDictionary<OperationKind, bool>());

// Avoid creating the delegate if the value already exists
bool canCast;
if (!wrappedSyntax.TryGetValue(operation.Kind, out canCast))
// Avoid creating a delegate and capture class
if (!wrappedSyntax.TryGetValue(operation.Kind, out var canCast))
{
canCast = wrappedSyntax.GetOrAdd(
operation.Kind,
kind => underlyingType.GetTypeInfo().IsAssignableFrom(operation.GetType().GetTypeInfo()));
canCast = underlyingType.GetTypeInfo().IsAssignableFrom(operation.GetType().GetTypeInfo());
wrappedSyntax.TryAdd(operation.Kind, canCast);
}

return canCast;
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