merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/t/perf/p5310-pack-bitmaps.sh

@@ -0,0 +1,71 @@
+#!/bin/sh
+
+test_description='Tests pack performance using bitmaps'
+. ./perf-lib.sh
+
+test_perf_large_repo
+
+# note that we do everything through config,
+# since we want to be able to compare bitmap-aware
+# git versus non-bitmap git
+#
+# We intentionally use the deprecated pack.writebitmaps
+# config so that we can test against older versions of git.
+test_expect_success 'setup bitmap config' '
+	git config pack.writebitmaps true
+'
+
+test_perf 'repack to disk' '
+	git repack -ad
+'
+
+test_perf 'simulated clone' '
+	git pack-objects --stdout --all </dev/null >/dev/null
+'
+
+test_perf 'simulated fetch' '
+	have=$(git rev-list HEAD~100 -1) &&
+	{
+		echo HEAD &&
+		echo ^$have
+	} | git pack-objects --revs --stdout >/dev/null
+'
+
+test_perf 'pack to file' '
+	git pack-objects --all pack1 </dev/null >/dev/null
+'
+
+test_perf 'pack to file (bitmap)' '
+	git pack-objects --use-bitmap-index --all pack1b </dev/null >/dev/null
+'
+
+test_expect_success 'create partial bitmap state' '
+	# pick a commit to represent the repo tip in the past
+	cutoff=$(git rev-list HEAD~100 -1) &&
+	orig_tip=$(git rev-parse HEAD) &&
+
+	# now kill off all of the refs and pretend we had
+	# just the one tip
+	rm -rf .git/logs .git/refs/* .git/packed-refs &&
+	git update-ref HEAD $cutoff &&
+
+	# and then repack, which will leave us with a nice
+	# big bitmap pack of the "old" history, and all of
+	# the new history will be loose, as if it had been pushed
+	# up incrementally and exploded via unpack-objects
+	git repack -Ad &&
+
+	# and now restore our original tip, as if the pushes
+	# had happened
+	git update-ref HEAD $orig_tip
+'
+
+test_perf 'clone (partial bitmap)' '
+	git pack-objects --stdout --all </dev/null >/dev/null
+'
+
+test_perf 'pack to file (partial bitmap)' '
+	git pack-objects --use-bitmap-index --all pack2b </dev/null >/dev/null
+'
+
+test_done