Allocations: Unroll AdditionalFile extension method

[sharwell]

Accounts for 5037MB allocations in https://developercommunity.visualstudio.com/t/Visual-Studio-2022:-High-CPU-usage-by-Se/10378039

sonar-dotnet/analyzers/src/SonarAnalyzer.Common/Extensions/AnalyzerOptionsExtensions.cs

Line 37 in ab9c515

options.AdditionalFiles.FirstOrDefault(x => x.Path is not null && Path.GetFileName(x.Path).Equals(fileName, StringComparison.OrdinalIgnoreCase));

[pavel-mikula-sonarsource]

This is a great catch! Thank you for reporting it.

Do you know from user logs how many additional files user had?
We could add case insensitive .EndsWith pre-check, but if he has 1 or 2 files, it will not fix the problem.
We could not use the API and do our own string-only based check too.

I have a feeling that we call that method way too often and fine-tuning the implementation could have no impact. What do you think of caching the value and using AnalyzerOptions as a key? In practice, the cache would never get purged (unless we purge it above a certain size). At the same time, the naive idea is that there shouldn't be too many different sets of AdditionalFiles during the memory lifetime of the analyzer. Or is there? As we would prevent GC from collecting the unique instances.

[sharwell]

It should be possible to slice the string after the final \ or / and compare the resulting ReadOnlySpan<char>, instead of allocating a substring.

[martin-strecker-sonarsource]

The measurement of a dotnet build of akka with dotnet sonarscanner begin of a SQ EE instance and "Sonar Way" profile revealed that Path.GetFileName (allocates strings) and AdditionalFiles.FirstOrDefault (allocates a delegate and a capture class) are the main source of allocations by far:

These two allocations contribute 1GB for the string + 700MB for the delegate + 260 MB for the capture class out of 11,3 GB total. We are also responsible for SymbolDisplay allocations shown above. The driver is here TypeHelper.IsMatch in Sonar-Security:
https://github.com/SonarSource/sonar-security/blob/b33150486bec9c1d61fd30b01a03c388a845b0c7/frontend/csharp/src/SonarAnalyzer.Security/Helpers/TypeHelper.cs#L31-L32

Note: I stopped capturing in the middle of the build after 30 minutes.

[martin-strecker-sonarsource]

We could add case insensitive .EndsWith pre-check, but if he has 1 or 2 files, it will not fix the problem.

There is an overload that takes a StringComparison so we should be fine. There are just two things to do:

• Unroll FirstOrDefault to a foreach to avoid the delegate and capture class allocations (1GB saving).
• Use EndsWith(StringComparison.OrdinalIgnoreCase) instead of Path.GetFileName. Another 1GB saving.