C++: Fix join orders in virtual dispatch computation

[MathiasVP]

This PR improves the performance of C/C++'s virtual dispatch computation in two ways:

• A minor performance improvement: Switch to doublyBoundedFastTC instead of fastTC. We already have good bounds on the end-point so we might as well make use of them here.
• A major performance improvement: Instead of computing the pairCand up front and then joining it with the edgePlus relation we start by computing edgePlus and then we join it with the body of pairCand. This has a major impact on large C/C++ databases at Microsoft (the time taken to compute virtual dispatch on a fresh DB is reduced by 10x in some cases).

Before (canceled before completion):

[2026-03-26 16:04:48] Tuple counts for DataFlowDispatch::TrackVirtualDispatch<noDisp>::pairCand/4#3fd492b3/4@696edeu1 after 4m39s:
  863412     ~0%        {3} r1 = SCAN `DataFlowDispatch::TrackVirtualDispatch<noDisp>::mostSpecific/2#8aef19c1` OUTPUT In.2, In.0, In.1
  863412     ~2%        {3}    | JOIN WITH DataFlowPrivate::TSourceCallable#54d42094 ON FIRST 1 OUTPUT Lhs.1, Rhs.1 'callable', Lhs.2
  1157251367 ~1024%     {4}    | JOIN WITH `DataFlowDispatch::TrackVirtualDispatch<d1>::qualifierOfVirtualCallImpl/3#5649cb98_201#join_rhs` ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'callable', Lhs.2, Rhs.2
  1462970099 ~871%      {4}    | JOIN WITH `TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<noDisp>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<noDisp>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<noDisp>::qualifierOfVirtualCall>::PathNodeFwd.getNode/0#dispred#8901ad56_10#join_rhs` ON FIRST 1 OUTPUT Rhs.1 'p2', Lhs.1 'callable', Lhs.2, Lhs.3
  974405553  ~784%      {4}    | JOIN WITH `TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<noDisp>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<noDisp>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<noDisp>::qualifierOfVirtualCall>::reachRev/1#ab50895d` ON FIRST 1 OUTPUT Lhs.0 'p2', Lhs.1 'callable', Lhs.2, Lhs.3
  919333500  ~748%      {4}    | JOIN WITH `num#TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<noDisp>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<noDisp>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<noDisp>::qualifierOfVirtualCall>::TPathNodeSink#eea8db44_1#join_rhs` ON FIRST 1 OUTPUT Lhs.3, Lhs.1 'callable', Lhs.2, Lhs.0 'p2'
  919328485  ~781%      {4}    | JOIN WITH DataFlowPrivate::TNormalCall#0f63d738 ON FIRST 1 OUTPUT Lhs.2, Lhs.1 'callable', Lhs.3 'p2', Rhs.1 'call'
  5348269387 ~949%      {4}    | JOIN WITH `DataFlowDispatch::qualifierSourceImpl/2#9b5eb2f5_10#join_rhs` ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'callable', Lhs.2 'p2', Lhs.3 'call'
  7135273052 ~909%      {4}    | JOIN WITH `TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<noDisp>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<noDisp>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<noDisp>::qualifierOfVirtualCall>::PathNodeFwd.getNode/0#dispred#8901ad56_10#join_rhs` ON FIRST 1 OUTPUT Rhs.1 'p1', Lhs.1 'callable', Lhs.2 'p2', Lhs.3 'call'
  7131364481 ~908%      {4}    | JOIN WITH `TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<noDisp>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<noDisp>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<noDisp>::qualifierOfVirtualCall>::PathNodeFwd.isSource/0#dispred#88b6728d` ON FIRST 1 OUTPUT Lhs.0 'p1', Lhs.1 'callable', Lhs.2 'p2', Lhs.3 'call'
  3333681000 ~877%      {4}    | JOIN WITH `TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<noDisp>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<noDisp>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<noDisp>::qualifierOfVirtualCall>::reachRev/1#ab50895d` ON FIRST 1 OUTPUT Lhs.0 'p1', Lhs.2 'p2', Lhs.1 'callable', Lhs.3 'call'
                        return r1

After (pairCand is now inlined):

[2026-03-26 16:21:55] (854s) Tuple counts for DataFlowDispatch::d5/1#fb855fd5/2@136c8ccu after 16.1s:
  282744     ~0%         {2} r1 = JOIN `TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<d4>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierOfVirtualCall>::reachRev/1#60f80b02` WITH `TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<d4>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierOfVirtualCall>::reachRev/1#60f80b02` ON FIRST 1 OUTPUT Lhs.0, Lhs.0
  
  32290878   ~1%         {2} r2 = `doublyBoundedFastTC:TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<d4>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierOfVirtualCall>::edges/2#1a906743_10#higher_order_body:_DataFlowDispatch::TrackVirtualDispatch<d4>::isSink/1#41abce53_TypeTrackingImpl::TypeTracking<Locati__#higher_order_body:DataFlowDispatch::TrackVirtualDispatch<d4>::isSource/1#3bcd6175` UNION r1
  32290878   ~0%         {2}    | JOIN WITH `TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<d4>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierOfVirtualCall>::reachRev/1#60f80b02` ON FIRST 1 OUTPUT Lhs.1, Lhs.0
  32197673   ~0%         {2}    | JOIN WITH `TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<d4>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierOfVirtualCall>::PathNodeFwd.isSource/0#dispred#5abd6574` ON FIRST 1 OUTPUT Lhs.0, Lhs.1
  32197673   ~1%         {2}    | JOIN WITH `TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<d4>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierOfVirtualCall>::reachRev/1#60f80b02` ON FIRST 1 OUTPUT Lhs.1, Lhs.0
  32097255   ~0%         {2}    | JOIN WITH `num#TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<d4>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierOfVirtualCall>::TPathNodeSink#87fa68f5_1#join_rhs` ON FIRST 1 OUTPUT Lhs.1, Lhs.0
  32097255   ~3%         {2}    | JOIN WITH `TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<d4>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierOfVirtualCall>::PathNodeFwd.getNode/0#dispred#191e1ea3` ON FIRST 1 OUTPUT Lhs.1, Rhs.1
  32097255   ~1%         {2}    | JOIN WITH `TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<d4>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierOfVirtualCall>::PathNodeFwd.getNode/0#dispred#191e1ea3` ON FIRST 1 OUTPUT Rhs.1, Lhs.1
  32171721   ~1%         {3}    | JOIN WITH `DataFlowDispatch::TrackVirtualDispatch<d1>::qualifierOfVirtualCallImpl/3#5649cb98` ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Rhs.2
  32171721   ~0%         {3}    | JOIN WITH DataFlowPrivate::TNormalCall#0f63d738 ON FIRST 1 OUTPUT Lhs.2, Lhs.1, Rhs.1 'call'
  1893840121 ~0%         {4}    | JOIN WITH `DataFlowDispatch::TrackVirtualDispatch<d4>::mostSpecific/2#3e05b0ea` ON FIRST 1 OUTPUT Lhs.1, Rhs.1, Lhs.2 'call', Rhs.2
  49769362   ~21935%     {2}    | JOIN WITH `DataFlowDispatch::qualifierSourceImpl/2#9b5eb2f5` ON FIRST 2 OUTPUT Lhs.3, Lhs.2 'call'
  471745     ~104%       {2}    | JOIN WITH DataFlowPrivate::TSourceCallable#54d42094 ON FIRST 1 OUTPUT Lhs.1 'call', Rhs.1 'result'
                          return r2

and then after a small join order fix:

[2026-03-26 17:06:05] (1050s) Tuple counts for DataFlowDispatch::d5/1#fb855fd5/2@6c7ad81n after 922ms:
  282744   ~1%         {2} r1 = JOIN `TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<d4>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierOfVirtualCall>::reachRev/1#60f80b02` WITH `TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<d4>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierOfVirtualCall>::reachRev/1#60f80b02` ON FIRST 1 OUTPUT Lhs.0, Lhs.0

  32290878 ~3%         {2} r2 = `doublyBoundedFastTC:TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<d4>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierOfVirtualCall>::edges/2#1a906743_10#higher_order_body:_DataFlowDispatch::TrackVirtualDispatch<d4>::isSink/1#41abce53_TypeTrackingImpl::TypeTracking<Locati__#higher_order_body:DataFlowDispatch::TrackVirtualDispatch<d4>::isSource/1#3bcd6175` UNION r1
  32290878 ~0%         {2}    | JOIN WITH `TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<d4>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierOfVirtualCall>::reachRev/1#60f80b02` ON FIRST 1 OUTPUT Lhs.1, Lhs.0
  32197673 ~3%         {2}    | JOIN WITH `TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<d4>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierOfVirtualCall>::PathNodeFwd.isSource/0#dispred#5abd6574` ON FIRST 1 OUTPUT Lhs.1, Lhs.0
  32097255 ~3%         {2}    | JOIN WITH `num#TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<d4>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierOfVirtualCall>::TPathNodeSink#87fa68f5_1#join_rhs` ON FIRST 1 OUTPUT Lhs.0, Lhs.1
  32097255 ~0%         {2}    | JOIN WITH `TypeTrackingImpl::TypeTracking<Location::Location,DataFlowDispatch::TrackVirtualDispatch<d4>::TtInput>::TypeTrack<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierSource>::Graph<DataFlowDispatch::TrackVirtualDispatch<d4>::qualifierOfVirtualCall>::PathNodeFwd.getNode/0#dispred#191e1ea3` ON FIRST 1 OUTPUT Rhs.1, Lhs.1
  32171721 ~0%         {3}    | JOIN WITH `DataFlowDispatch::TrackVirtualDispatch<d1>::qualifierOfVirtualCallImpl/3#5649cb98` ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Rhs.2
  32171721 ~0%         {3}    | JOIN WITH DataFlowPrivate::TNormalCall#0f63d738 ON FIRST 1 OUTPUT Lhs.1, Lhs.2, Rhs.1 'call'
  49768855 ~21935%     {2}    | JOIN WITH `DataFlowDispatch::TrackVirtualDispatch<d4>::mostSpecificForSource/2#c1de398d` ON FIRST 2 OUTPUT Rhs.2, Lhs.2 'call'
  567835   ~146%       {2}    | JOIN WITH DataFlowPrivate::TSourceCallable#54d42094 ON FIRST 1 OUTPUT Lhs.1 'call', Rhs.1 'result'
                        return r2

[Copilot]

Pull request overview

This PR targets performance in C/C++ virtual dispatch computation by improving transitive-closure and join-order behavior in TrackVirtualDispatch, aiming to reduce evaluation cost on large databases.

Changes:

• Replace fastTC(edges/2) with doublyBoundedFastTC(edges/2, isSource/1, isSink/1) for edgePlus.
• Inline/restructure pairCand computation by factoring out mostSpecificForSource and adding bindingset / inline_late to influence evaluation order.