D6428: rust-discovery: using the children cache in add_missing

[gracinet (Georges Racinet)]

gracinet added a comment.


  This revision is new. At the time I submitted the previous series, it was almost always the case that the advantage of the C `reachableroots2()` over the Rust ``dagop::range()` was more than compensated by sampling been done in Rust instead of Python.
  I originally planned to finish that one and submit it as a follow-up optimization, but now it's necessary to prevent being slower in the fastest cases where there's no sampling.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D6428

To: gracinet, #hg-reviewers
Cc: durin42, kevincox, mercurial-devel