checkout: avoid unnecessary match_pathspec calls

In checkout_paths() we do this

 - for all updated items, call match_pathspec
 - for all items, call match_pathspec (inside unmerge_cache)
 - for all items, call match_pathspec (for showing "path .. is unmerged)
 - for updated items, call match_pathspec and update paths

That's a lot of duplicate match_pathspec(s) and the function is not
exactly cheap to be called so many times, especially on large indexes.
This patch makes it call match_pathspec once per updated index entry,
save the result in ce_flags and reuse the results in the following
loops.

The changes in 0a1283b (checkout $tree $path: do not clobber local
changes in $path not in $tree - 2011-09-30) limit the affected paths
to ones we read from $tree. We do not do anything to other modified
entries in this case, so the "for all items" above could be modified
to "for all updated items". But..

The command's behavior now is modified slightly: unmerged entries that
match $path, but not updated by $tree, are now NOT touched.  Although
this should be considered a bug fix, not a regression. A new test is
added for this change.

And while at there, free ps_matched after use.

The following command is tested on webkit, 215k entries. The pattern
is chosen mainly to make match_pathspec sweat:

git checkout -- "*[a-zA-Z]*[a-zA-Z]*[a-zA-Z]*"

        before      after
real    0m3.493s    0m2.737s
user    0m2.239s    0m1.586s
sys     0m1.252s    0m1.151s

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/t/t2022-checkout-paths.sh b/t/t2022-checkout-paths.sh
index 56090d2..8e3545d 100755
--- a/t/t2022-checkout-paths.sh
+++ b/t/t2022-checkout-paths.sh
@@ -39,4 +39,26 @@ test_expect_success 'checking out paths out of a tree does not clobber unrelated
 	test_cmp expect.next2 dir/next2
 '
 
+test_expect_success 'do not touch unmerged entries matching $path but not in $tree' '
+	git checkout next &&
+	git reset --hard &&
+
+	cat dir/common >expect.common &&
+	EMPTY_SHA1=$(git hash-object -w --stdin </dev/null) &&
+	git rm dir/next0 &&
+	cat >expect.next0 <<-EOF &&
+	100644 $EMPTY_SHA1 1	dir/next0
+	100644 $EMPTY_SHA1 2	dir/next0
+	EOF
+	git update-index --index-info <expect.next0 &&
+
+	git checkout master dir &&
+
+	test_cmp expect.common dir/common &&
+	test_path_is_file dir/master &&
+	git diff --exit-code master dir/master &&
+	git ls-files -s dir/next0 >actual.next0 &&
+	test_cmp expect.next0 actual.next0
+'
+
 test_done