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
$ hg init
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ ls
a
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1"
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
B should disappear
$ ls
a