performance: speedup computation of mutable revisions
In their current state, revset calls can be very costly, as we test
predicates on the entire repository. The "mutable" filter is used
during branch cache loading operation. We need to make it fast.
This change drops revset calls in favor of direct testing of the
phase of a changeset.
Performance test on my Mercurial checkout
- 19857 total changesets,
- 1646 mutable revision
Before:
! mutable
! wall 0.032405
After:
! mutable
! wall 0.001469
Performance test on a Mozilla central checkout:
- 117293 total changesets,
- 1 mutable changeset,
Before:
! mutable
! wall 0.188636
After:
! mutable
! wall 0.000022
copyright (c) 2006-2010 David JEAN LOUIS
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