Trim analyzer: Implement intrinsics handling of object.GetType

[vitek-karas]

This fixes #86921.

Analyzer so far didn't handle correct data flow around object.GetType and DynamicallyAccessedMembersAttribute on types. This change implements that behavior.

Main changes:

• Move IValueWithStaticType to the shared code and refactor its existing usage in trimmer/AOT to use the shared code instead. Also implement it for the analyzer.
• Refactor method call handling in the analyzer to a single static method which is called both from the visitor and from the patterns.
• In order to get same behavior, start tracking values for all fields and method parameters.

Outside of the actual fix, the other main change is that analyzer now tracks values for all fields and method parameters, regardless if their type is interesting to analysis. This is necessary because the static type now matters, even if it's something else than System.Type.

The effect of that is that the analyzer now recognizes lot more invalid cases because it can determine if the value is something unrecognizable. Before the change such values where tracked as "empty", and thus analysis ignored them. Now they're track as "value of a field, without annotations" which can lead to producing more warnings.

That means this resolves lot of cases in dotnet/linker#2755. At least all the test cases which were added because of that bug, or which expected different behavior because of it now produce consistent behavior with trimmer/NativeAOT.

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Issue Details

---

This fixes #86921.

Analyzer so far didn't handle correct data flow around object.GetType and DynamicallyAccessedMembersAttribute on types. This change implements that behavior.

Main changes:

• Move IValueWithStaticType to the shared code and refactor its existing usage in trimmer/AOT to use the shared code instead. Also implement it for the analyzer.
• Refactor method call handling in the analyzer to a single static method which is called both from the visitor and from the patterns.
• In order to get same behavior, start tracking values for all fields and method parameters.

Outside of the actual fix, the other main change is that analyzer now tracks values for all fields and method parameters, regardless if their type is interesting to analysis. This is necessary because the static type now matters, even if it's something else than System.Type.

The effect of that is that the analyzer now recognizes lot more invalid cases because it can determine if the value is something unrecognizable. Before the change such values where tracked as "empty", and thus analysis ignored them. Now they're track as "value of a field, without annotations" which can lead to producing more warnings.

That means this effectively fixes dotnet/linker#2755. At least all the test cases which were added because of that bug, or which expected different behavior because of it now produce consistent behavior with trimmer/NativeAOT.

Author:	vitek-karas
Assignees:	vitek-karas
Labels:	area-Tools-ILLink
Milestone:	9.0.0

[vitek-karas]

Tracking more values means that the analyzer is potentially slower. I'll try to measure this somehow.

[agocke]

This looks good -- but I'm not sure why some things weren't being tracked before.

That is, my understanding of why typeof(Blah).MakeGenericType doesn't warn is that the receiver wasn't tracked for some reason. But typeof(Blah) is definitely an instance of System.Type. So why wasn't it tracked?

[sbomer]

One question about the treatment of "empty", otherwise LGTM, thanks!