A big part of FCS analysis time is spent in GC

[auduchinok]

I'm looking at various perf snapshots and seeing that in many of them about 20-30% of the time that FCS takes to analyse a project graph is spent in GC. Here's the last example, GC takes 41 seconds:

Could we work on finding a systematic approach that would allow us to reduce allocations where possible? Possible things are:

• reuse some collection objects
• don't create intermediate lists and use state machine list builders instead
• use arrays and mutation
• don't recalculate things where possible

Some of these things aren't very idiomatic in a functional language, but when talking about compiler and editor analysis engine, I think a better performance should matter more than being completely idiomatic.

[dsyme]

I'd encourage a focus on performance, not allocations. Allocations happen, they are not necessarily bad. Often the gains come from avoiding running code at all more than from removing allocations

Historically the biggest gains by @TIHan have been from removing transient LOH allocations. Those are really important to find and nail down.