C++: Performance fix for existsCompleteWithName

[jbj]

No description provided.

[geoffw0]

Code change LGTM.

[jbj]

@pavgust I've tried to investigate the cause of this performance regression in code that hasn't changed for a long time. I think the slowdown is a side effect of an optimiser improvement, possibly the fix for QL-878. Whatever it was, it caused a slight simplification of how the strictcount range and term were compiled, which meant there was no longer a need for a #shared predicate. But I think that #shared predicate was helping performance by deduplicating tuples in the pipeline in exactly the place where it happened to be needed.

In conclusion, I think the optimiser is to blame for this fix being necessary, but I think the optimiser is doing a better job in 1.22 than in 1.21 even though random chance meant this PR went from being nice-to-have to being critical.

For the record, this is the RA from 1.21:

EVALUATE NONRECURSIVE RELATION:
  SYNTHETIC ResolveClass::existsCompleteWithName#ff#shared(unique int arg0, extensional string arg1) :-
    {1} r1 = JOIN is_complete WITH ResolveClass::getTopLevelClassName#ff ON is_complete.<0>=ResolveClass::getTopLevelClassName#ff.<0> OUTPUT FIELDS {ResolveClass::getTopLevelClassName#ff.<1>}
    {2} r2 = JOIN r1 WITH ResolveClass::getTopLevelClassName#ff_10#join_rhs ON r1.<0>=ResolveClass::getTopLevelClassName#ff_10#join_rhs.<0> OUTPUT FIELDS {ResolveClass::getTopLevelClassName#ff_10#join_rhs.<1>,r1.<0>}
    return r2

EVALUATE NONRECURSIVE RELATION:
  SYNTHETIC ResolveClass::existsCompleteWithName#ff#count_range(extensional string arg0, unique int arg1) :-
    {2} r1 = JOIN ResolveClass::existsCompleteWithName#ff#shared WITH is_complete ON ResolveClass::existsCompleteWithName#ff#shared.<0>=is_complete.<0> OUTPUT FIELDS {ResolveClass::existsCompleteWithName#ff#shared.<1>,ResolveClass::existsCompleteWithName#ff#shared.<0>}
    return r1

EVALUATE NONRECURSIVE RELATION:
  SYNTHETIC ResolveClass::existsCompleteWithName#ff#count_term(extensional string arg0, unique int arg1) :-
    {2} r1 = JOIN ResolveClass::existsCompleteWithName#ff#shared WITH is_complete ON ResolveClass::existsCompleteWithName#ff#shared.<0>=is_complete.<0> OUTPUT FIELDS {ResolveClass::existsCompleteWithName#ff#shared.<0>,ResolveClass::existsCompleteWithName#ff#shared.<1>}
    {2} r2 = JOIN r1 WITH usertypes ON r1.<0>=usertypes.<0> OUTPUT FIELDS {r1.<1>,r1.<0>}
    return r2

EVALUATE NONRECURSIVE RELATION:
  SYNTHETIC ResolveClass::existsCompleteWithName#ff#join_rhs(extensional string arg0, int arg1) :-
    {2} r1 = AGGREGATE ResolveClass::existsCompleteWithName#ff#count_range, ResolveClass::existsCompleteWithName#ff#count_term ON {} WITH COUNT OUTPUT {ResolveClass::existsCompleteWithName#ff#count_term.<0>,agg.<0>}
    return r1

EVALUATE NONRECURSIVE RELATION:
  ResolveClass::existsCompleteWithName#ff(extensional string name, unique int d) :-
    {2} r1 = JOIN is_complete WITH ResolveClass::getTopLevelClassName#ff ON is_complete.<0>=ResolveClass::getTopLevelClassName#ff.<0> OUTPUT FIELDS {ResolveClass::getTopLevelClassName#ff.<1>,is_complete.<0>}
    {3} r2 = JOIN r1 WITH ResolveClass::existsCompleteWithName#ff#join_rhs ON r1.<0>=ResolveClass::existsCompleteWithName#ff#join_rhs.<0> OUTPUT FIELDS {r1.<1>,r1.<0>,ResolveClass::existsCompleteWithName#ff#join_rhs.<1>}
    {3} r3 = SELECT r2 ON CONSTANT r2.<2>=1
    {2} r4 = SCAN r3 OUTPUT FIELDS {r3.<1>,r3.<0>}
    return r4

This is the RA from 1.22:

EVALUATE NONRECURSIVE RELATION:
  SYNTHETIC ResolveClass::existsCompleteWithName#ff#count_range(extensional string arg0, unique int arg1) :-
    {1} r1 = JOIN is_complete WITH ResolveClass::getTopLevelClassName#ff ON is_complete.<0>=ResolveClass::getTopLevelClassName#ff.<0> OUTPUT FIELDS {ResolveClass::getTopLevelClassName#ff.<1>}
    {2} r2 = JOIN r1 WITH ResolveClass::getTopLevelClassName#ff_10#join_rhs ON r1.<0>=ResolveClass::getTopLevelClassName#ff_10#join_rhs.<0> OUTPUT FIELDS {ResolveClass::getTopLevelClassName#ff_10#join_rhs.<1>,r1.<0>}
    {2} r3 = JOIN r2 WITH is_complete ON r2.<0>=is_complete.<0> OUTPUT FIELDS {r2.<1>,r2.<0>}
    return r3

EVALUATE NONRECURSIVE RELATION:
  SYNTHETIC ResolveClass::existsCompleteWithName#ff#join_rhs(extensional string arg0, int arg1) :-
    {2} r1 = AGGREGATE ResolveClass::existsCompleteWithName#ff#count_range, ResolveClass::existsCompleteWithName#ff#count_range ON {} WITH COUNT OUTPUT {ResolveClass::existsCompleteWithName#ff#count_range.<0>,agg.<0>}
    return r1

EVALUATE NONRECURSIVE RELATION:
  ResolveClass::existsCompleteWithName#ff(extensional string name, unique int d) :-
    {2} r1 = JOIN is_complete WITH ResolveClass::getTopLevelClassName#ff ON is_complete.<0>=ResolveClass::getTopLevelClassName#ff.<0> OUTPUT FIELDS {ResolveClass::getTopLevelClassName#ff.<1>,is_complete.<0>}
    {3} r2 = JOIN r1 WITH ResolveClass::existsCompleteWithName#ff#join_rhs ON r1.<0>=ResolveClass::existsCompleteWithName#ff#join_rhs.<0> OUTPUT FIELDS {r1.<1>,r1.<0>,ResolveClass::existsCompleteWithName#ff#join_rhs.<1>}
    {3} r3 = SELECT r2 ON CONSTANT r2.<2>=1
    {2} r4 = SCAN r3 OUTPUT FIELDS {r3.<1>,r3.<0>}
    return r4

[jbj]

(RA edited)