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Cache RetargetingParameterSymbol.TypeWithAnnotations to avoid ~8.3% allocations in a trace #69011

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merged 2 commits into from
Jul 15, 2023
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Cache RetargetingParameterSymbol.TypeWithAnnotations to avoid ~8.3% allocations in a trace #69011

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90ec1a6
Cache RetargetingParameterSymbol.TypeWithAnnotations to avoid ~3.5% a…
Youssef1313 Jul 12, 2023
ca72dde
Use Interlocked.CompareExchange along with TypeWithAnnotations.Boxed
Youssef1313 Jul 13, 2023
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9 changes: 8 additions & 1 deletion src/Compilers/CSharp/Portable/Symbols/Retargeting/RetargetingParameterSymbol.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,8 @@ internal abstract class RetargetingParameterSymbol : WrappedParameterSymbol
/// </summary>
private ImmutableArray<CSharpAttributeData> _lazyCustomAttributes;

private TypeWithAnnotations? _lazyTypeWithAnnotations;
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protected RetargetingParameterSymbol(ParameterSymbol underlyingParameter)
: base(underlyingParameter)
{
Expand All @@ -38,7 +40,12 @@ public sealed override TypeWithAnnotations TypeWithAnnotations
{
get
{
return this.RetargetingModule.RetargetingTranslator.Retarget(_underlyingParameter.TypeWithAnnotations, RetargetOptions.RetargetPrimitiveTypesByTypeCode);
if (!_lazyTypeWithAnnotations.HasValue)
{
_lazyTypeWithAnnotations = this.RetargetingModule.RetargetingTranslator.Retarget(_underlyingParameter.TypeWithAnnotations, RetargetOptions.RetargetPrimitiveTypesByTypeCode);
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Nullable<TypeWithAnnotations> is not thread-safe. Is this field accessed from multiple threads?

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@cston Yeah I was chatting with Sam about this. I didn't find an appropriate existing helper, so Sam is working on merging helpers that are not available in the compilers layer with those available in the compilers layer.

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No additional helpers are necessary, that's what https://sourceroslyn.io/#Microsoft.CodeAnalysis.CSharp/Symbols/TypeWithAnnotations.cs,e5078e3d5fd03b05,references is for.

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If the goal is to avoid recalculating the type, it may be sufficient to just cache the TypeSymbol.

private TypeSymbol? _lazyType;

public sealed override TypeWithAnnotations TypeWithAnnotations
{
    get
    {
        var underlyingType = _underlyingParameter.TypeWithAnnotations;
        var translator = RetargetingModule.RetargetingTranslator;
        if (_lazyType is null)
        {
            Interlocked.CompareExchange(ref _lazyType,
                translator.Retarget(underlyingType.Type,
                    RetargetOptions.RetargetPrimitiveTypesByTypeCode),
                null);
        }
        var newModifiers = translator.RetargetModifiers(underlyingType.CustomModifiers, out _);
        return underlyingType.WithTypeAndModifiers(_lazyType, newModifiers);
    }
}

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@cston In the trace I provided, this property is accessed 12,833,732 times during 3 minutes. So I think it's worth to just cache the whole thing.

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No additional helpers are necessary, that's what https://sourceroslyn.io/#Microsoft.CodeAnalysis.CSharp/Symbols/TypeWithAnnotations.cs,e5078e3d5fd03b05,references is for.

Does this suggest it like that?

if (_lazyTypeWithAnnotations is null)
{
    Interlocked.CompareExchange(ref _lazyTypeWithAnnotations, new TypeWithAnnotations.Boxed(......), null);
}

I think that would still risk calculating it twice if two threads concurrently accessed the property.

What Sam suggested was something to be like this:

return LazyInitialization.EnsureInitialized(
    ref _lazyTypeWithAnnotations,
    static self => self.RetargetingModule.RetargetingTranslator.Retarget(self._underlyingParameter.TypeWithAnnotations, RetargetOptions.RetargetPrimitiveTypesByTypeCode),
    this);

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@sharwell sharwell Jul 13, 2023 •
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@333fred The helpers are lazy initialization helpers for reference types, and are unrelated to the fact that this is a value type. Even after switching to TypeWithAnnotations.Boxed, we'd want to use the helper method for clarity. See #69017

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We should switch to TypeWithAnnotations.Boxed, which we use to cache this information in symbols. There should be many examples. No special helpers are necessary and the change shouldn't be blocked on that.

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I used TypeWithAnnotations.Boxed for now. After #69017 is merged, I can switch to another helper if that would be better.

}

return _lazyTypeWithAnnotations.Value;
}
}

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