dirstate: when calling rebuild(), avoid some N^2 codepaths
I had a user repo with 200k files in it. Calling `hg debugrebuilddirstate` took
tens of minutes (I didn't wait for it). In that situation,
changedfiles==allfiles, and both are lists. This meant that we had to run an
average of 100k comparisons, for each of 200k files, just to check whether a
file needed to have normallookup called (it always did), or drop.
While it's probably not a huge issue, in my very awkward synthetic benchmark I
wrote (not using a benchmark library or anything), I was seeing some slowdowns
for small-changedfiles and very-large-allfiles invocations, with an inflection
somewhere around 10 items in changedfiles (regardless of the size of allfiles);
above 10 items in changedfiles, the new code appears to always be faster. For
the case of 50k files in changedfiles and the same items in allfiles, I'm seeing
differences of 15s of just running comparisons vs. 0.003793s. I haven't bothered
to run a comparison of 200k items in changedfiles and allfiles. :)
Differential Revision: https://phab.mercurial-scm.org/D7665
$ hg init
$ echo foo > a
$ echo foo > b
$ hg add a b
$ hg ci -m "test"
$ echo blah > a
$ hg ci -m "branch a"
$ hg co 0
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo blah > b
$ hg ci -m "branch b"
created new head
$ HGMERGE=true hg merge 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg ci -m "merge b/a -> blah"
$ hg co 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ HGMERGE=true hg merge 2
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg ci -m "merge a/b -> blah"
created new head
$ hg log
changeset: 4:2ee31f665a86
tag: tip
parent: 1:96155394af80
parent: 2:92cc4c306b19
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: merge a/b -> blah
changeset: 3:e16a66a37edd
parent: 2:92cc4c306b19
parent: 1:96155394af80
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: merge b/a -> blah
changeset: 2:92cc4c306b19
parent: 0:5e0375449e74
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: branch b
changeset: 1:96155394af80
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: branch a
changeset: 0:5e0375449e74
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: test
$ hg debugindex --changelog
rev linkrev nodeid p1 p2
0 0 5e0375449e74 000000000000 000000000000
1 1 96155394af80 5e0375449e74 000000000000
2 2 92cc4c306b19 5e0375449e74 000000000000
3 3 e16a66a37edd 92cc4c306b19 96155394af80
4 4 2ee31f665a86 96155394af80 92cc4c306b19
revision 1
$ hg manifest --debug 1
79d7492df40aa0fa093ec4209be78043c181f094 644 a
2ed2a3912a0b24502043eae84ee4b279c18b90dd 644 b
revision 2
$ hg manifest --debug 2
2ed2a3912a0b24502043eae84ee4b279c18b90dd 644 a
79d7492df40aa0fa093ec4209be78043c181f094 644 b
revision 3
$ hg manifest --debug 3
79d7492df40aa0fa093ec4209be78043c181f094 644 a
79d7492df40aa0fa093ec4209be78043c181f094 644 b
revision 4
$ hg manifest --debug 4
79d7492df40aa0fa093ec4209be78043c181f094 644 a
79d7492df40aa0fa093ec4209be78043c181f094 644 b
$ hg debugindex a
rev linkrev nodeid p1 p2
0 0 2ed2a3912a0b 000000000000 000000000000
1 1 79d7492df40a 2ed2a3912a0b 000000000000
$ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
checked 5 changesets with 4 changes to 2 files