C#: Restrict dataflow node creation to source and source-referenced entities

[smowton]

This addresses a problem observed when libraries define a very large number of types with large class hierarchies, for example as part of generated code. Since user code is very unlikely to refer to all or even most of them, by excluding such code from dataflow node generation and therefore from the C# dataflow hooks' idea of a "relevant" type, we can make many of the type predicates defined in DataFlowPrivate.qll very much cheaper.

See discarded variant #17482 for some discussion.

[smowton]

DCA results are very positive -- no alert changes; considerably reduced cost for some projects. Started QA at https://github.com/github/codeql-qa-ops/issues/198

[smowton]

QA results are also very positive: positive time changes (a small number of large repositories exhibiting fairly large improvements, similar to DCA), and no alert differences (a small number of repos showing some changes in quality queries, but none reproducible locally, indicating these are cases of nondeterministic database creation).

[hvitved]

Really great work, nice to see how this significantly improves performance on some projects. I only have two minor comments.

[smowton]

@hvitved changes applied; change note added.

[smowton]

Confirmed that for the original problem database that sparked this, the predicates taking >=1s are:

Most expensive predicates for completed query XSS.ql:
        time  | evals |   max @ iter | predicate
        ------|-------|--------------|----------
        42.6s |       |              | Implements::getAnImplementedInterfaceMemberForSubType/2#8542025f_120#join_rhs@b020baas
        23.1s |    39 |  6.2s @ 3    | Implements::getAnImplementedInterfaceMemberForSubType/2#8542025f@6c8e02no
        18.1s |    21 |  9.9s @ 9    | Conversion::convRefTypeRefType/2#3840d258#reorder_1_0@627975wt
        15.9s |       |              | Member::Overridable.getAnUltimateImplementee/0#58db54c4@874a91rj
          14s |       |              | OverridableCallable::OverridableCallable.getInherited/1#dispred#78b84fce@ef4e925t
        12.6s |       |              | Member::Overridable.getAnUltimateImplementee/0#58db54c4@62ab75cc
         7.3s |       |              | Unification::Unification::Cached::typeConstraintSubsumes/2#ad05ac89@c5f84549
         6.9s |       |              | Unification::Unification::Cached::typeConstraintUnifiable/2#1c317d19@c3c4f8oo
         5.1s |       |              | __Location::Location.hasLocationInfo/5#dispred#45331897__Element::Element.getALocation/0#dispred#0f2__#join_rhs@be6b8dnq
         4.7s |    34 | 872ms @ 13   | #Type::ValueOrRefType.getABaseType/0#dispred#4af8c7e0Plus#bf@8af016sk
         4.5s |    34 | 643ms @ 8    | #Type::ValueOrRefType.getABaseType/0#dispred#4af8c7e0Plus#bf@f26df4uu
         4.1s |    15 |  3.2s @ 2    | Implements::getACompatibleRelevantInterfaceMember0/2#dffa6396#bff@fddef8s8
           4s |       |              | Member::Overridable.getAnUltimateImplementee/0#58db54c4@9a47c2q5
         3.7s |       |              | ExternalFlow::parameterQualifiedTypeNamesToString/1#c0c070ba@702c056v
         3.5s |       |              | DataFlowPrivate::commonSubTypeGeneral/2#55d9b3a5@7a7bd5u1
         3.3s |    35 | 306ms @ 12   | OverridableCallable::OverridableCallable.getInherited0/1#4f8a07e6#ffb@cad181ec
         2.6s |       |              | Implements::getARelevantInterfaceMemberCandidate/1#f08a099b@9c0f5bas
         2.5s |       |              | _AspNetCore::MicrosoftAspNetCoreMvcControllerBaseClass#82d5f012_Element::NamedElement.getName/0#disp__#higher_order_body@6cd67cqa
         2.3s |    20 |  1.6s @ 10   | Conversion::convRefTypeNonNull/2#80d5061d@627979wt
         2.1s |       |              | Implements::getAPossibleImplementor/1#9c7b7cfd@dfb416ri
         1.9s |    35 | 204ms @ 8    | _@virtualizable_Member::Modifiable.hasModifier/1#dispred#72531dc6_Member::Overridable.getExplicitlyI__#antijoin_rhs@L0#0b5f3
         1.9s |       |              | Implements::getAPotentialRelevantInterfaceMemberAux/4#bd1fda6f_1230#join_rhs@d568985e
         1.8s |    69 | 229ms @ 27   | OverridableCallable::OverridableCallable.isDeclaringSubType/1#c77dd2ec@3fb43wev
         1.8s |       |              | OverridableCallable::OverridableCallable.getInherited1/1#dispred#5fc48a55#ffb_120#join_rhs@2501a0b8
         1.8s |    15 | 987ms @ 6    | __ExternalFlow::QN::getTypeArgumentsQualifiedName/2#376a6b72#prev_ExternalFlow::QN::getTypeArguments__#join_rhs@L2#5be36
         1.8s |    15 | 994ms @ 3    | __Generics::ConstructedGeneric.getTypeArgument/1#dispred#3e84d95d_Generics::ConstructedGeneric.getTy__#join_rhs@L2#647b8
         1.6s |    17 |  1.3s @ 3    | __Unification::Gvn::ConstructedGvnTypeList.toStringConstructedPart/2#9ffaf943#prev_Unification::Gvn:__#join_rhs@L6#7e566
         1.4s |       |              | OverridableCallable::OverridableCallable.getInherited1/1#dispred#5fc48a55#ffb@1506b53o
         1.3s |       |              | ServiceStack::ServiceClass#3ba1ecfc@7a99465f
         1.2s |       |              | OverridableCallable::OverridableCallable.isDeclaringSubType/2#87f9be27_021#join_rhs@0ea8647v
         1.2s |       |              | Conversion::implicitConversion/2#bed063da@9bd65fet
         1.1s |       |              | Conversion::implicitConversion/2#bed063da@1e997f2t
           1s |       |              | ExternalFlow::parameterQualifiedTypeNamesToString/1#c0c070ba@4f5434p0
           1s |       |              | __Attribute::Attribute.getType/0#dispred#0bee65bf#bf_Element::NamedElement.getName/0#dispred#6665e8e__#antijoin_rhs@664fcdft
           1s |    15 | 636ms @ 3    | __Generics::ConstructedGeneric.getTypeArgument/1#dispred#3e84d95d_Generics::ConstructedGeneric.getTy__#join_rhs@L2#8ea80

Note DataFlowPrivate::commonSubTypeGeneral at 3.5s