Reduce LOH allocations in MetadataWriter #78245
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In draft mode until test insertion perf numbers come back Will add justification if the perf numbers come back good
ghost
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Area-Compilers
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ToddGrun
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jaredpar
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Apr 22, 2025
This was referenced Apr 24, 2025
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MetadataWriter's use of Dictionary leads to LOH allocations in the Roslyn CA process. Instead, switch over to SegmentedDictionary to reduce that pressure.
From the Roslyn C# completion speedometer test, about 16% of all LOH allocations occur adding to MetadataWriter._signatureIndex. This type represents the 2nd highest entry on the LOH list.
After changing to a SegmentedDictionary these LOH are no longer present.