Reduce allocations in SourceGeneratedDocumentIdentity.Generate #80292
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1) The ArrayBuilder that was being used commonly ends up exceeding the re-use size threshold, thus negating it's pooling benefit 2) The ArrayBuilder.ToArray call can be replaced by an upfront array allocation as the size of the array is easy to determine 3) The Encoding.GetBytes calls can be changed to a non-allocating version 4) In NET, can avoid creating the SHA256 object 5) In NET, can use the HashData call to avoid allocating a return array 6) In NET, can create a guid without needing to create a new array
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| + Encoding.Unicode.GetByteCount(hintName); | ||
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| var hashInput = new byte[hashInputLength]; |
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Is there no streaming version that can avoid this alloc in the first place?
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Not that I could find (at least on the Encoding class)
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What about IncrementalHash.Create(Sha256), and then just append the data, instead of needing the initial array to copy into?
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we also have the Checksum type. Which, TBH, feels pretty appropriate for this use case :)
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OK, reworked with using Checksums instead. It does seem easier this way.
| Array.Resize(ref hash, 16); | ||
| var guid = new Guid(hash); | ||
| #if NET | ||
| Span<byte> bytesToChecksum = stackalloc byte[16]; |
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Do we have a constant we can use for this?
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I don't think there is anything in the Guid class accessible to us. A regexp search for "guid.*16" in Roslyn has several hits, but nothing is sticking out as a good candidate to use.
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Found this while looking at a profile for the razor speedometer test. This isn't a huge allocator, but it's a couple MB of allocations that should be mostly removed.