I have a few suggested performance improvements in DataFlowAnalysis:

1. .Any() call on PooledSortedSet<T> is Enumerable.Any extension method call, that type does not have its own Any method like some types do, e.g. ArrayBuilder<T>. As Enumerable.Any performs type checks, it should be better to check .Count.

   I believe there's a standard CA1860 rule for those kind of cases. As it's included in Minimum analysis mode, I also prepared PR Use AnalysisMode=minimum in Microsoft.CodeAnalysis.NetAnalyzers and fix errors (perf rules) #50367 to start catching these errors.

2. There are a few issues with the part of code in RunCore method:

   • It calls .Where allocating an enumerable
   • Delegate passed to .Where creates closure
   • Enumerable returned by .Where is enumerated multiple times.

   I'd suggest to re-write that part with a simple loop to avoid these issues.
   Regarding multiple enumeration, there's a standard CA1851 rule, I believe it was added in .NET 7.

3. The delegate passed to .Any call in HasUnprocessedPredecessorBlock also creates closure.