manifestmerge: use dicthelpers.diff and join This patch improves manifestmerge performance significantly. In a repository with 170,000 files, the following results were observed on a clean working directory. Revision '.' adds one file. hg perfmergecalculate -r . - before: 0.41 seconds - after: 0.13 seconds hg perfmergecalculate -r .^ - before: 0.53 seconds - after: 0.24 seconds Comparing against '.' is much faster than comparing against '.^' because with '.', the wctx and p2 manifest strings have the same identity, so comparisons are simply pointer equality. With '.^', the strings have different identities so we need to perform memcmps. Any operation that uses manifestmerge benefits. - hg update . goes from 2.04 seconds to 1.75 - hg update .^ goes from 2.52 seconds to 2.25 - hg rebase -r . -d .~6 (involves 4 merges) goes from 11.8 seconds to 10.8