revsetlang: build optimized tree by helper function
This should make optimize() more readable, but it doubles the parsing cost.
(original)
$ python -m timeit -n10000 -s 'from mercurial import revsetlang as L' \
'L.optimize(L.analyze(L.parse("::tip")))'
10000 loops, best of 3: 18.1 usec per loop
(this patch)
$ python -m timeit -n10000 -s 'from mercurial import revsetlang as L' \
'L._treecache.clear(); L.optimize(L.analyze(L.parse("::tip")))'
10000 loops, best of 3: 48.4 usec per loop
30usec isn't dominant compared to the revset evaluation, but that is a cost.
That's why a parsed tree is cached, which can benefit in hgweb or chg server.