diff --git a/t/lib-merge.sh b/t/lib-merge.sh
new file mode 100644
index 0000000000..8734ebfc17
--- /dev/null
+++ b/t/lib-merge.sh
@@ -0,0 +1,13 @@
+# Helper functions used by merge tests.
+
+test_expect_merge_algorithm () {
+	status_for_recursive=$1 status_for_ort=$2
+	shift 2
+
+	if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	then
+		test_expect_${status_for_ort} "$@"
+	else
+		test_expect_${status_for_recursive} "$@"
+	fi
+}
diff --git a/t/t6400-merge-df.sh b/t/t6400-merge-df.sh
index f1b84617af..9da0838216 100755
--- a/t/t6400-merge-df.sh
+++ b/t/t6400-merge-df.sh
@@ -81,7 +81,12 @@ test_expect_success 'modify/delete + directory/file conflict' '
 
 	test 5 -eq $(git ls-files -s | wc -l) &&
 	test 4 -eq $(git ls-files -u | wc -l) &&
-	test 1 -eq $(git ls-files -o | wc -l) &&
+	if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	then
+		test 0 -eq $(git ls-files -o | wc -l)
+	else
+		test 1 -eq $(git ls-files -o | wc -l)
+	fi &&
 
 	test_path_is_file letters/file &&
 	test_path_is_file letters.txt &&
@@ -97,7 +102,12 @@ test_expect_success 'modify/delete + directory/file conflict; other way' '
 
 	test 5 -eq $(git ls-files -s | wc -l) &&
 	test 4 -eq $(git ls-files -u | wc -l) &&
-	test 1 -eq $(git ls-files -o | wc -l) &&
+	if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	then
+		test 0 -eq $(git ls-files -o | wc -l)
+	else
+		test 1 -eq $(git ls-files -o | wc -l)
+	fi &&
 
 	test_path_is_file letters/file &&
 	test_path_is_file letters.txt &&
diff --git a/t/t6402-merge-rename.sh b/t/t6402-merge-rename.sh
index bbbba3dcbf..3f64f62224 100755
--- a/t/t6402-merge-rename.sh
+++ b/t/t6402-merge-rename.sh
@@ -320,7 +320,12 @@ test_expect_success 'Rename+D/F conflict; renamed file merges but dir in way' '
 
 	test_i18ngrep "CONFLICT (modify/delete): dir/file-in-the-way" output &&
 	test_i18ngrep "Auto-merging dir" output &&
-	test_i18ngrep "Adding as dir~HEAD instead" output &&
+	if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	then
+		test_i18ngrep "moving it to dir~HEAD instead" output
+	else
+		test_i18ngrep "Adding as dir~HEAD instead" output
+	fi &&
 
 	test 3 -eq "$(git ls-files -u | wc -l)" &&
 	test 2 -eq "$(git ls-files -u dir/file-in-the-way | wc -l)" &&
@@ -342,7 +347,12 @@ test_expect_success 'Same as previous, but merged other way' '
 	! grep "error: refusing to lose untracked file at" errors &&
 	test_i18ngrep "CONFLICT (modify/delete): dir/file-in-the-way" output &&
 	test_i18ngrep "Auto-merging dir" output &&
-	test_i18ngrep "Adding as dir~renamed-file-has-no-conflicts instead" output &&
+	if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	then
+		test_i18ngrep "moving it to dir~renamed-file-has-no-conflicts instead" output
+	else
+		test_i18ngrep "Adding as dir~renamed-file-has-no-conflicts instead" output
+	fi &&
 
 	test 3 -eq "$(git ls-files -u | wc -l)" &&
 	test 2 -eq "$(git ls-files -u dir/file-in-the-way | wc -l)" &&
@@ -397,7 +407,12 @@ test_expect_success 'Rename+D/F conflict; renamed file cannot merge and dir in t
 	test_must_fail git merge --strategy=recursive dir-in-way &&
 
 	test 5 -eq "$(git ls-files -u | wc -l)" &&
-	test 3 -eq "$(git ls-files -u dir | grep -v file-in-the-way | wc -l)" &&
+	if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	then
+		test 3 -eq "$(git ls-files -u dir~HEAD | wc -l)"
+	else
+		test 3 -eq "$(git ls-files -u dir | grep -v file-in-the-way | wc -l)"
+	fi &&
 	test 2 -eq "$(git ls-files -u dir/file-in-the-way | wc -l)" &&
 
 	test_must_fail git diff --quiet &&
@@ -415,7 +430,12 @@ test_expect_success 'Same as previous, but merged other way' '
 	test_must_fail git merge --strategy=recursive renamed-file-has-conflicts &&
 
 	test 5 -eq "$(git ls-files -u | wc -l)" &&
-	test 3 -eq "$(git ls-files -u dir | grep -v file-in-the-way | wc -l)" &&
+	if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	then
+		test 3 -eq "$(git ls-files -u dir~renamed-file-has-conflicts | wc -l)"
+	else
+		test 3 -eq "$(git ls-files -u dir | grep -v file-in-the-way | wc -l)"
+	fi &&
 	test 2 -eq "$(git ls-files -u dir/file-in-the-way | wc -l)" &&
 
 	test_must_fail git diff --quiet &&
@@ -471,7 +491,12 @@ test_expect_success 'both rename source and destination involved in D/F conflict
 	git checkout -q rename-dest^0 &&
 	test_must_fail git merge --strategy=recursive source-conflict &&
 
-	test 1 -eq "$(git ls-files -u | wc -l)" &&
+	if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	then
+		test 2 -eq "$(git ls-files -u | wc -l)"
+	else
+		test 1 -eq "$(git ls-files -u | wc -l)"
+	fi &&
 
 	test_must_fail git diff --quiet &&
 
@@ -505,34 +530,63 @@ test_expect_success 'setup pair rename to parent of other (D/F conflicts)' '
 	git commit -m "Rename one/file -> two"
 '
 
-test_expect_success 'pair rename to parent of other (D/F conflicts) w/ untracked dir' '
-	git checkout -q rename-one^0 &&
-	mkdir one &&
-	test_must_fail git merge --strategy=recursive rename-two &&
+if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+then
+	test_expect_success 'pair rename to parent of other (D/F conflicts) w/ untracked dir' '
+		git checkout -q rename-one^0 &&
+		mkdir one &&
+		test_must_fail git merge --strategy=recursive rename-two &&
 
-	test 2 -eq "$(git ls-files -u | wc -l)" &&
-	test 1 -eq "$(git ls-files -u one | wc -l)" &&
-	test 1 -eq "$(git ls-files -u two | wc -l)" &&
+		test 4 -eq "$(git ls-files -u | wc -l)" &&
+		test 2 -eq "$(git ls-files -u one | wc -l)" &&
+		test 2 -eq "$(git ls-files -u two | wc -l)" &&
 
-	test_must_fail git diff --quiet &&
+		test_must_fail git diff --quiet &&
 
-	test 4 -eq $(find . | grep -v .git | wc -l) &&
+		test 3 -eq $(find . | grep -v .git | wc -l) &&
 
-	test_path_is_dir one &&
-	test_path_is_file one~rename-two &&
-	test_path_is_file two &&
-	test "other" = $(cat one~rename-two) &&
-	test "stuff" = $(cat two)
-'
+		test_path_is_file one &&
+		test_path_is_file two &&
+		test "other" = $(cat one) &&
+		test "stuff" = $(cat two)
+	'
+else
+	test_expect_success 'pair rename to parent of other (D/F conflicts) w/ untracked dir' '
+		git checkout -q rename-one^0 &&
+		mkdir one &&
+		test_must_fail git merge --strategy=recursive rename-two &&
+
+		test 2 -eq "$(git ls-files -u | wc -l)" &&
+		test 1 -eq "$(git ls-files -u one | wc -l)" &&
+		test 1 -eq "$(git ls-files -u two | wc -l)" &&
+
+		test_must_fail git diff --quiet &&
+
+		test 4 -eq $(find . | grep -v .git | wc -l) &&
+
+		test_path_is_dir one &&
+		test_path_is_file one~rename-two &&
+		test_path_is_file two &&
+		test "other" = $(cat one~rename-two) &&
+		test "stuff" = $(cat two)
+	'
+fi
 
 test_expect_success 'pair rename to parent of other (D/F conflicts) w/ clean start' '
 	git reset --hard &&
 	git clean -fdqx &&
 	test_must_fail git merge --strategy=recursive rename-two &&
 
-	test 2 -eq "$(git ls-files -u | wc -l)" &&
-	test 1 -eq "$(git ls-files -u one | wc -l)" &&
-	test 1 -eq "$(git ls-files -u two | wc -l)" &&
+	if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	then
+		test 4 -eq "$(git ls-files -u | wc -l)" &&
+		test 2 -eq "$(git ls-files -u one | wc -l)" &&
+		test 2 -eq "$(git ls-files -u two | wc -l)"
+	else
+		test 2 -eq "$(git ls-files -u | wc -l)" &&
+		test 1 -eq "$(git ls-files -u one | wc -l)" &&
+		test 1 -eq "$(git ls-files -u two | wc -l)"
+	fi &&
 
 	test_must_fail git diff --quiet &&
 
@@ -572,12 +626,22 @@ test_expect_success 'check handling of differently renamed file with D/F conflic
 	git checkout -q first-rename^0 &&
 	test_must_fail git merge --strategy=recursive second-rename &&
 
-	test 5 -eq "$(git ls-files -s | wc -l)" &&
-	test 3 -eq "$(git ls-files -u | wc -l)" &&
-	test 1 -eq "$(git ls-files -u one | wc -l)" &&
-	test 1 -eq "$(git ls-files -u two | wc -l)" &&
-	test 1 -eq "$(git ls-files -u original | wc -l)" &&
-	test 2 -eq "$(git ls-files -o | wc -l)" &&
+	if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	then
+		test 5 -eq "$(git ls-files -s | wc -l)" &&
+		test 3 -eq "$(git ls-files -u | wc -l)" &&
+		test 1 -eq "$(git ls-files -u one~HEAD | wc -l)" &&
+		test 1 -eq "$(git ls-files -u two~second-rename | wc -l)" &&
+		test 1 -eq "$(git ls-files -u original | wc -l)" &&
+		test 0 -eq "$(git ls-files -o | wc -l)"
+	else
+		test 5 -eq "$(git ls-files -s | wc -l)" &&
+		test 3 -eq "$(git ls-files -u | wc -l)" &&
+		test 1 -eq "$(git ls-files -u one | wc -l)" &&
+		test 1 -eq "$(git ls-files -u two | wc -l)" &&
+		test 1 -eq "$(git ls-files -u original | wc -l)" &&
+		test 2 -eq "$(git ls-files -o | wc -l)"
+	fi &&
 
 	test_path_is_file one/file &&
 	test_path_is_file two/file &&
diff --git a/t/t6404-recursive-merge.sh b/t/t6404-recursive-merge.sh
index 332cfc53fd..b1c3d4dda4 100755
--- a/t/t6404-recursive-merge.sh
+++ b/t/t6404-recursive-merge.sh
@@ -118,12 +118,22 @@ test_expect_success 'mark rename/delete as unmerged' '
 	test_tick &&
 	git commit -m rename &&
 	test_must_fail git merge delete &&
-	test 1 = $(git ls-files --unmerged | wc -l) &&
+	if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	then
+		test 2 = $(git ls-files --unmerged | wc -l)
+	else
+		test 1 = $(git ls-files --unmerged | wc -l)
+	fi &&
 	git rev-parse --verify :2:a2 &&
 	test_must_fail git rev-parse --verify :3:a2 &&
 	git checkout -f delete &&
 	test_must_fail git merge rename &&
-	test 1 = $(git ls-files --unmerged | wc -l) &&
+	if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	then
+		test 2 = $(git ls-files --unmerged | wc -l)
+	else
+		test 1 = $(git ls-files --unmerged | wc -l)
+	fi &&
 	test_must_fail git rev-parse --verify :2:a2 &&
 	git rev-parse --verify :3:a2
 '
diff --git a/t/t6416-recursive-corner-cases.sh b/t/t6416-recursive-corner-cases.sh
index fd98989b14..887c2195a9 100755
--- a/t/t6416-recursive-corner-cases.sh
+++ b/t/t6416-recursive-corner-cases.sh
@@ -3,6 +3,7 @@
 test_description='recursive merge corner cases involving criss-cross merges'
 
 . ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-merge.sh
 
 #
 #  L1  L2
@@ -537,9 +538,15 @@ test_expect_success 'setup differently handled merges of directory/file conflict
 
 		git checkout B^0 &&
 		test_must_fail git merge C^0 &&
-		git clean -fd &&
-		git rm -rf a/ &&
-		git rm a &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			git rm -rf a/ &&
+			git rm a~HEAD
+		else
+			git clean -fd &&
+			git rm -rf a/ &&
+			git rm a
+		fi &&
 		git cat-file -p B:a >a2 &&
 		git add a2 &&
 		git commit -m D2 &&
@@ -558,7 +565,12 @@ test_expect_success 'setup differently handled merges of directory/file conflict
 
 		git checkout C^0 &&
 		test_must_fail git merge B^0 &&
-		git clean -fd &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			git rm a~B^0
+		else
+			git clean -fd
+		fi &&
 		git rm -rf a/ &&
 		test_write_lines 1 2 3 4 5 6 7 8 >a &&
 		git add a &&
@@ -567,9 +579,15 @@ test_expect_success 'setup differently handled merges of directory/file conflict
 
 		git checkout C^0 &&
 		test_must_fail git merge B^0 &&
-		git clean -fd &&
-		git rm -rf a/ &&
-		git rm a &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			git rm -rf a/ &&
+			git rm a~B^0
+		else
+			git clean -fd &&
+			git rm -rf a/ &&
+			git rm a
+		fi &&
 		test_write_lines 1 2 3 4 5 6 7 8 >a2 &&
 		git add a2 &&
 		git commit -m E4 &&
@@ -587,18 +605,34 @@ test_expect_success 'merge of D1 & E1 fails but has appropriate contents' '
 
 		test_must_fail git merge -s recursive E1^0 &&
 
-		git ls-files -s >out &&
-		test_line_count = 2 out &&
-		git ls-files -u >out &&
-		test_line_count = 1 out &&
-		git ls-files -o >out &&
-		test_line_count = 1 out &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			git ls-files -s >out &&
+			test_line_count = 3 out &&
+			git ls-files -u >out &&
+			test_line_count = 2 out &&
+			git ls-files -o >out &&
+			test_line_count = 1 out &&
 
-		git rev-parse >expect    \
-			A:ignore-me  B:a &&
-		git rev-parse   >actual   \
-			:0:ignore-me :2:a &&
-		test_cmp expect actual
+			git rev-parse >expect    \
+				A:ignore-me  B:a  D1:a &&
+			git rev-parse   >actual   \
+				:0:ignore-me :1:a :2:a &&
+			test_cmp expect actual
+		else
+			git ls-files -s >out &&
+			test_line_count = 2 out &&
+			git ls-files -u >out &&
+			test_line_count = 1 out &&
+			git ls-files -o >out &&
+			test_line_count = 1 out &&
+
+			git rev-parse >expect    \
+				A:ignore-me  B:a &&
+			git rev-parse   >actual   \
+				:0:ignore-me :2:a &&
+			test_cmp expect actual
+		fi
 	)
 '
 
@@ -612,18 +646,34 @@ test_expect_success 'merge of E1 & D1 fails but has appropriate contents' '
 
 		test_must_fail git merge -s recursive D1^0 &&
 
-		git ls-files -s >out &&
-		test_line_count = 2 out &&
-		git ls-files -u >out &&
-		test_line_count = 1 out &&
-		git ls-files -o >out &&
-		test_line_count = 1 out &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			git ls-files -s >out &&
+			test_line_count = 3 out &&
+			git ls-files -u >out &&
+			test_line_count = 2 out &&
+			git ls-files -o >out &&
+			test_line_count = 1 out &&
 
-		git rev-parse >expect    \
-			A:ignore-me  B:a &&
-		git rev-parse   >actual   \
-			:0:ignore-me :3:a &&
-		test_cmp expect actual
+			git rev-parse >expect    \
+				A:ignore-me  B:a  D1:a &&
+			git rev-parse   >actual   \
+				:0:ignore-me :1:a :3:a &&
+			test_cmp expect actual
+		else
+			git ls-files -s >out &&
+			test_line_count = 2 out &&
+			git ls-files -u >out &&
+			test_line_count = 1 out &&
+			git ls-files -o >out &&
+			test_line_count = 1 out &&
+
+			git rev-parse >expect    \
+				A:ignore-me  B:a &&
+			git rev-parse   >actual   \
+				:0:ignore-me :3:a &&
+			test_cmp expect actual
+		fi
 	)
 '
 
@@ -637,17 +687,32 @@ test_expect_success 'merge of D1 & E2 fails but has appropriate contents' '
 
 		test_must_fail git merge -s recursive E2^0 &&
 
-		git ls-files -s >out &&
-		test_line_count = 4 out &&
-		git ls-files -u >out &&
-		test_line_count = 3 out &&
-		git ls-files -o >out &&
-		test_line_count = 2 out &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			git ls-files -s >out &&
+			test_line_count = 5 out &&
+			git ls-files -u >out &&
+			test_line_count = 4 out &&
+			git ls-files -o >out &&
+			test_line_count = 1 out &&
 
-		git rev-parse >expect    \
-			B:a   E2:a/file  C:a/file   A:ignore-me &&
-		git rev-parse   >actual   \
-			:2:a  :3:a/file  :1:a/file  :0:ignore-me &&
+			git rev-parse >expect    \
+				B:a       D1:a      E2:a/file  C:a/file   A:ignore-me &&
+			git rev-parse   >actual   \
+				:1:a~HEAD :2:a~HEAD :3:a/file  :1:a/file  :0:ignore-me
+		else
+			git ls-files -s >out &&
+			test_line_count = 4 out &&
+			git ls-files -u >out &&
+			test_line_count = 3 out &&
+			git ls-files -o >out &&
+			test_line_count = 2 out &&
+
+			git rev-parse >expect    \
+				B:a    E2:a/file  C:a/file   A:ignore-me &&
+			git rev-parse   >actual   \
+				:2:a   :3:a/file  :1:a/file  :0:ignore-me
+		fi &&
 		test_cmp expect actual &&
 
 		test_path_is_file a~HEAD
@@ -664,17 +729,32 @@ test_expect_success 'merge of E2 & D1 fails but has appropriate contents' '
 
 		test_must_fail git merge -s recursive D1^0 &&
 
-		git ls-files -s >out &&
-		test_line_count = 4 out &&
-		git ls-files -u >out &&
-		test_line_count = 3 out &&
-		git ls-files -o >out &&
-		test_line_count = 2 out &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			git ls-files -s >out &&
+			test_line_count = 5 out &&
+			git ls-files -u >out &&
+			test_line_count = 4 out &&
+			git ls-files -o >out &&
+			test_line_count = 1 out &&
 
-		git rev-parse >expect    \
-			B:a   E2:a/file  C:a/file   A:ignore-me &&
-		git rev-parse   >actual   \
-			:3:a  :2:a/file  :1:a/file  :0:ignore-me &&
+			git rev-parse >expect    \
+				B:a       D1:a      E2:a/file  C:a/file   A:ignore-me &&
+			git rev-parse   >actual   \
+				:1:a~D1^0 :3:a~D1^0 :2:a/file  :1:a/file  :0:ignore-me
+		else
+			git ls-files -s >out &&
+			test_line_count = 4 out &&
+			git ls-files -u >out &&
+			test_line_count = 3 out &&
+			git ls-files -o >out &&
+			test_line_count = 2 out &&
+
+			git rev-parse >expect    \
+				B:a   E2:a/file  C:a/file   A:ignore-me &&
+			git rev-parse   >actual   \
+				:3:a  :2:a/file  :1:a/file  :0:ignore-me
+		fi &&
 		test_cmp expect actual &&
 
 		test_path_is_file a~D1^0
@@ -706,7 +786,7 @@ test_expect_success 'merge of D1 & E3 succeeds' '
 	)
 '
 
-test_expect_success 'merge of D1 & E4 notifies user a and a2 are related' '
+test_expect_merge_algorithm failure success 'merge of D1 & E4 puts merge of a and a2 in both a and a2' '
 	test_when_finished "git -C directory-file reset --hard" &&
 	test_when_finished "git -C directory-file clean -fdqx" &&
 	(
@@ -724,7 +804,7 @@ test_expect_success 'merge of D1 & E4 notifies user a and a2 are related' '
 		test_line_count = 1 out &&
 
 		git rev-parse >expect                  \
-			A:ignore-me  B:a   D1:a  E4:a2 &&
+			A:ignore-me  B:a   E4:a2  E4:a2 &&
 		git rev-parse   >actual                \
 			:0:ignore-me :1:a~Temporary\ merge\ branch\ 2  :2:a  :3:a2 &&
 		test_cmp expect actual
@@ -1069,7 +1149,7 @@ test_expect_success 'setup symlink modify/modify' '
 	)
 '
 
-test_expect_failure 'check symlink modify/modify' '
+test_expect_merge_algorithm failure success 'check symlink modify/modify' '
 	(
 		cd symlink-modify-modify &&
 
@@ -1135,7 +1215,7 @@ test_expect_success 'setup symlink add/add' '
 	)
 '
 
-test_expect_failure 'check symlink add/add' '
+test_expect_merge_algorithm failure success 'check symlink add/add' '
 	(
 		cd symlink-add-add &&
 
@@ -1223,7 +1303,7 @@ test_expect_success 'setup submodule modify/modify' '
 	)
 '
 
-test_expect_failure 'check submodule modify/modify' '
+test_expect_merge_algorithm failure success 'check submodule modify/modify' '
 	(
 		cd submodule-modify-modify &&
 
@@ -1311,7 +1391,7 @@ test_expect_success 'setup submodule add/add' '
 	)
 '
 
-test_expect_failure 'check submodule add/add' '
+test_expect_merge_algorithm failure success 'check submodule add/add' '
 	(
 		cd submodule-add-add &&
 
@@ -1386,7 +1466,7 @@ test_expect_success 'setup conflicting entry types (submodule vs symlink)' '
 	)
 '
 
-test_expect_failure 'check conflicting entry types (submodule vs symlink)' '
+test_expect_merge_algorithm failure success 'check conflicting entry types (submodule vs symlink)' '
 	(
 		cd submodule-symlink-add-add &&
 
diff --git a/t/t6422-merge-rename-corner-cases.sh b/t/t6422-merge-rename-corner-cases.sh
index 3375eaf4e7..78bfaf17f0 100755
--- a/t/t6422-merge-rename-corner-cases.sh
+++ b/t/t6422-merge-rename-corner-cases.sh
@@ -4,6 +4,7 @@ test_description="recursive merge corner cases w/ renames but not criss-crosses"
 # t6036 has corner cases that involve both criss-cross merges and renames
 
 . ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-merge.sh
 
 test_setup_rename_delete_untracked () {
 	test_create_repo rename-delete-untracked &&
@@ -312,15 +313,18 @@ test_expect_success 'rename/directory conflict + clean content merge' '
 		git ls-files -u >out &&
 		test_line_count = 1 out &&
 		git ls-files -o >out &&
-		test_line_count = 2 out &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			test_line_count = 1 out
+		else
+			test_line_count = 2 out
+		fi &&
 
 		echo 0 >expect &&
 		git cat-file -p base:file >>expect &&
 		echo 7 >>expect &&
 		test_cmp expect newfile~HEAD &&
 
-		test $(git rev-parse :2:newfile) = $(git hash-object expect) &&
-
 		test_path_is_file newfile/realfile &&
 		test_path_is_file newfile~HEAD
 	)
@@ -343,7 +347,12 @@ test_expect_success 'rename/directory conflict + content merge conflict' '
 		git ls-files -u >out &&
 		test_line_count = 3 out &&
 		git ls-files -o >out &&
-		test_line_count = 2 out &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			test_line_count = 1 out
+		else
+			test_line_count = 2 out
+		fi &&
 
 		git cat-file -p left-conflict:newfile >left &&
 		git cat-file -p base:file    >base &&
@@ -355,10 +364,16 @@ test_expect_success 'rename/directory conflict + content merge conflict' '
 			left base right &&
 		test_cmp left newfile~HEAD &&
 
-		git rev-parse >expect                                 \
-			base:file   left-conflict:newfile  right:file &&
-		git rev-parse >actual                                 \
-			:1:newfile  :2:newfile             :3:newfile &&
+		git rev-parse >expect   \
+			base:file       left-conflict:newfile right:file &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			git rev-parse >actual \
+				:1:newfile~HEAD :2:newfile~HEAD :3:newfile~HEAD
+		else
+			git rev-parse >actual \
+				:1:newfile      :2:newfile      :3:newfile
+		fi &&
 		test_cmp expect actual &&
 
 		test_path_is_file newfile/realfile &&
@@ -878,7 +893,7 @@ test_setup_rad () {
 	)
 }
 
-test_expect_failure 'rad-check: rename/add/delete conflict' '
+test_expect_merge_algorithm failure success 'rad-check: rename/add/delete conflict' '
 	test_setup_rad &&
 	(
 		cd rad &&
@@ -951,7 +966,7 @@ test_setup_rrdd () {
 	)
 }
 
-test_expect_failure 'rrdd-check: rename/rename(2to1)/delete/delete conflict' '
+test_expect_merge_algorithm failure success 'rrdd-check: rename/rename(2to1)/delete/delete conflict' '
 	test_setup_rrdd &&
 	(
 		cd rrdd &&
@@ -1040,7 +1055,7 @@ test_setup_mod6 () {
 	)
 }
 
-test_expect_failure 'mod6-check: chains of rename/rename(1to2) and rename/rename(2to1)' '
+test_expect_merge_algorithm failure success 'mod6-check: chains of rename/rename(1to2) and rename/rename(2to1)' '
 	test_setup_mod6 &&
 	(
 		cd mod6 &&
diff --git a/t/t6423-merge-rename-directories.sh b/t/t6423-merge-rename-directories.sh
index 06b46af765..4ab133f489 100755
--- a/t/t6423-merge-rename-directories.sh
+++ b/t/t6423-merge-rename-directories.sh
@@ -26,6 +26,7 @@ test_description="recursive merge with directory renames"
 #                     files that might be renamed into each other's paths.)
 
 . ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-merge.sh
 
 
 ###########################################################################
@@ -301,11 +302,20 @@ test_expect_success '1d: Directory renames cause a rename/rename(2to1) conflict'
 		git cat-file -p :2:x/wham >expect &&
 		git cat-file -p :3:x/wham >other &&
 		>empty &&
-		test_must_fail git merge-file \
-			-L "HEAD" \
-			-L "" \
-			-L "B^0" \
-			expect empty other &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			test_must_fail git merge-file \
+				-L "HEAD:y/wham" \
+				-L "" \
+				-L "B^0:z/wham" \
+				expect empty other
+		else
+			test_must_fail git merge-file \
+				-L "HEAD" \
+				-L "" \
+				-L "B^0" \
+				expect empty other
+		fi &&
 		test_cmp expect x/wham
 	)
 '
@@ -1176,10 +1186,18 @@ test_expect_success '5d: Directory/file/file conflict due to directory rename' '
 		git ls-files -u >out &&
 		test_line_count = 1 out &&
 		git ls-files -o >out &&
-		test_line_count = 2 out &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			test_line_count = 1 out &&
 
-		git rev-parse >actual \
-			:0:y/b :0:y/c :0:z/d :0:y/f :2:y/d :0:y/d/e &&
+			git rev-parse >actual \
+			    :0:y/b :0:y/c :0:z/d :0:y/f :2:y/d~HEAD :0:y/d/e
+		else
+			test_line_count = 2 out &&
+
+			git rev-parse >actual \
+			    :0:y/b :0:y/c :0:z/d :0:y/f :2:y/d      :0:y/d/e
+		fi &&
 		git rev-parse >expect \
 			 O:z/b  O:z/c  B:z/d  B:z/f  A:y/d  B:y/d/e &&
 		test_cmp expect actual &&
@@ -1262,17 +1280,32 @@ test_expect_success '6a: Tricky rename/delete' '
 		test_must_fail git -c merge.directoryRenames=true merge -s recursive B^0 >out &&
 		test_i18ngrep "CONFLICT (rename/delete).*z/c.*y/c" out &&
 
-		git ls-files -s >out &&
-		test_line_count = 2 out &&
-		git ls-files -u >out &&
-		test_line_count = 1 out &&
-		git ls-files -o >out &&
-		test_line_count = 1 out &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			git ls-files -s >out &&
+			test_line_count = 3 out &&
+			git ls-files -u >out &&
+			test_line_count = 2 out &&
+			git ls-files -o >out &&
+			test_line_count = 1 out &&
 
-		git rev-parse >actual \
-			:0:y/b :3:y/c &&
-		git rev-parse >expect \
-			 O:z/b  O:z/c &&
+			git rev-parse >actual \
+				:0:y/b :1:y/c :3:y/c &&
+			git rev-parse >expect \
+				 O:z/b  O:z/c  O:z/c
+		else
+			git ls-files -s >out &&
+			test_line_count = 2 out &&
+			git ls-files -u >out &&
+			test_line_count = 1 out &&
+			git ls-files -o >out &&
+			test_line_count = 1 out &&
+
+			git rev-parse >actual \
+				:0:y/b :3:y/c &&
+			git rev-parse >expect \
+				 O:z/b  O:z/c
+		fi &&
 		test_cmp expect actual
 	)
 '
@@ -1339,7 +1372,7 @@ test_setup_6b1 () {
 	)
 }
 
-test_expect_failure '6b1: Same renames done on both sides, plus another rename' '
+test_expect_merge_algorithm failure success '6b1: Same renames done on both sides, plus another rename' '
 	test_setup_6b1 &&
 	(
 		cd 6b1 &&
@@ -1412,7 +1445,7 @@ test_setup_6b2 () {
 	)
 }
 
-test_expect_failure '6b2: Same rename done on both sides' '
+test_expect_merge_algorithm failure success '6b2: Same rename done on both sides' '
 	test_setup_6b2 &&
 	(
 		cd 6b2 &&
@@ -1799,11 +1832,20 @@ test_expect_success '7b: rename/rename(2to1), but only due to transitive rename'
 		git cat-file -p :2:y/d >expect &&
 		git cat-file -p :3:y/d >other &&
 		>empty &&
-		test_must_fail git merge-file \
-			-L "HEAD" \
-			-L "" \
-			-L "B^0" \
-			expect empty other &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			test_must_fail git merge-file \
+				-L "HEAD:y/d" \
+				-L "" \
+				-L "B^0:z/d" \
+				expect empty other
+		else
+			test_must_fail git merge-file \
+				-L "HEAD" \
+				-L "" \
+				-L "B^0" \
+				expect empty other
+		fi &&
 		test_cmp expect y/d
 	)
 '
@@ -1925,17 +1967,32 @@ test_expect_success '7d: transitive rename involved in rename/delete; how is it
 		test_must_fail git -c merge.directoryRenames=true merge -s recursive B^0 >out &&
 		test_i18ngrep "CONFLICT (rename/delete).*x/d.*y/d" out &&
 
-		git ls-files -s >out &&
-		test_line_count = 3 out &&
-		git ls-files -u >out &&
-		test_line_count = 1 out &&
-		git ls-files -o >out &&
-		test_line_count = 1 out &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			git ls-files -s >out &&
+			test_line_count = 4 out &&
+			git ls-files -u >out &&
+			test_line_count = 2 out &&
+			git ls-files -o >out &&
+			test_line_count = 1 out &&
 
-		git rev-parse >actual \
-			:0:y/b :0:y/c :3:y/d &&
-		git rev-parse >expect \
-			 O:z/b  O:z/c  O:x/d &&
+			git rev-parse >actual \
+				:0:y/b :0:y/c :1:y/d :3:y/d &&
+			git rev-parse >expect \
+				 O:z/b  O:z/c  O:x/d  O:x/d
+		else
+			git ls-files -s >out &&
+			test_line_count = 3 out &&
+			git ls-files -u >out &&
+			test_line_count = 1 out &&
+			git ls-files -o >out &&
+			test_line_count = 1 out &&
+
+			git rev-parse >actual \
+				:0:y/b :0:y/c :3:y/d &&
+			git rev-parse >expect \
+				 O:z/b  O:z/c  O:x/d
+		fi &&
 		test_cmp expect actual
 	)
 '
@@ -2016,17 +2073,32 @@ test_expect_success '7e: transitive rename in rename/delete AND dirs in the way'
 		test_must_fail git -c merge.directoryRenames=true merge -s recursive B^0 >out &&
 		test_i18ngrep "CONFLICT (rename/delete).*x/d.*y/d" out &&
 
-		git ls-files -s >out &&
-		test_line_count = 5 out &&
-		git ls-files -u >out &&
-		test_line_count = 1 out &&
-		git ls-files -o >out &&
-		test_line_count = 2 out &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			git ls-files -s >out &&
+			test_line_count = 6 out &&
+			git ls-files -u >out &&
+			test_line_count = 2 out &&
+			git ls-files -o >out &&
+			test_line_count = 1 out &&
 
-		git rev-parse >actual \
-			:0:x/d/f :0:y/d/g :0:y/b :0:y/c :3:y/d &&
-		git rev-parse >expect \
-			 A:x/d/f  A:y/d/g  O:z/b  O:z/c  O:x/d &&
+			git rev-parse >actual \
+				:0:x/d/f :0:y/d/g :0:y/b :0:y/c :1:y/d~B^0 :3:y/d~B^0 &&
+			git rev-parse >expect \
+				 A:x/d/f  A:y/d/g  O:z/b  O:z/c  O:x/d      O:x/d
+		else
+			git ls-files -s >out &&
+			test_line_count = 5 out &&
+			git ls-files -u >out &&
+			test_line_count = 1 out &&
+			git ls-files -o >out &&
+			test_line_count = 2 out &&
+
+			git rev-parse >actual \
+				:0:x/d/f :0:y/d/g :0:y/b :0:y/c :3:y/d &&
+			git rev-parse >expect \
+				 A:x/d/f  A:y/d/g  O:z/b  O:z/c  O:x/d
+		fi &&
 		test_cmp expect actual &&
 
 		git hash-object y/d~B^0 >actual &&
@@ -3142,6 +3214,7 @@ test_expect_success '10a: Overwrite untracked with normal rename/delete' '
 		echo important >z/d &&
 
 		test_must_fail git -c merge.directoryRenames=true merge -s recursive B^0 >out 2>err &&
+		test_path_is_missing .git/MERGE_HEAD &&
 		test_i18ngrep "The following untracked working tree files would be overwritten by merge" err &&
 
 		git ls-files -s >out &&
@@ -3211,21 +3284,34 @@ test_expect_success '10b: Overwrite untracked with dir rename + delete' '
 		echo contents >y/e &&
 
 		test_must_fail git -c merge.directoryRenames=true merge -s recursive B^0 >out 2>err &&
-		test_i18ngrep "CONFLICT (rename/delete).*Version B\^0 of y/d left in tree at y/d~B\^0" out &&
-		test_i18ngrep "Error: Refusing to lose untracked file at y/e; writing to y/e~B\^0 instead" out &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			test_path_is_missing .git/MERGE_HEAD &&
+			test_i18ngrep "error: The following untracked working tree files would be overwritten by merge" err &&
 
-		git ls-files -s >out &&
-		test_line_count = 3 out &&
-		git ls-files -u >out &&
-		test_line_count = 2 out &&
-		git ls-files -o >out &&
-		test_line_count = 5 out &&
+			git ls-files -s >out &&
+			test_line_count = 1 out &&
+			git ls-files -u >out &&
+			test_line_count = 0 out &&
+			git ls-files -o >out &&
+			test_line_count = 5 out
+		else
+			test_i18ngrep "CONFLICT (rename/delete).*Version B\^0 of y/d left in tree at y/d~B\^0" out &&
+			test_i18ngrep "Error: Refusing to lose untracked file at y/e; writing to y/e~B\^0 instead" out &&
 
-		git rev-parse >actual \
-			:0:y/b :3:y/d :3:y/e &&
-		git rev-parse >expect \
-			O:z/b  O:z/c  B:z/e &&
-		test_cmp expect actual &&
+			git ls-files -s >out &&
+			test_line_count = 3 out &&
+			git ls-files -u >out &&
+			test_line_count = 2 out &&
+			git ls-files -o >out &&
+			test_line_count = 5 out &&
+
+			git rev-parse >actual \
+				:0:y/b :3:y/d :3:y/e &&
+			git rev-parse >expect \
+				O:z/b  O:z/c  B:z/e &&
+			test_cmp expect actual
+		fi &&
 
 		echo very >expect &&
 		test_cmp expect y/c &&
@@ -3288,25 +3374,38 @@ test_expect_success '10c1: Overwrite untracked with dir rename/rename(1to2)' '
 		echo important >y/c &&
 
 		test_must_fail git -c merge.directoryRenames=true merge -s recursive B^0 >out 2>err &&
-		test_i18ngrep "CONFLICT (rename/rename)" out &&
-		test_i18ngrep "Refusing to lose untracked file at y/c; adding as y/c~B\^0 instead" out &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			test_path_is_missing .git/MERGE_HEAD &&
+			test_i18ngrep "error: The following untracked working tree files would be overwritten by merge" err &&
 
-		git ls-files -s >out &&
-		test_line_count = 6 out &&
-		git ls-files -u >out &&
-		test_line_count = 3 out &&
-		git ls-files -o >out &&
-		test_line_count = 3 out &&
+			git ls-files -s >out &&
+			test_line_count = 4 out &&
+			git ls-files -u >out &&
+			test_line_count = 0 out &&
+			git ls-files -o >out &&
+			test_line_count = 3 out
+		else
+			test_i18ngrep "CONFLICT (rename/rename)" out &&
+			test_i18ngrep "Refusing to lose untracked file at y/c; adding as y/c~B\^0 instead" out &&
 
-		git rev-parse >actual \
-			:0:y/a :0:y/b :0:x/d :1:x/c :2:w/c :3:y/c &&
-		git rev-parse >expect \
-			 O:z/a  O:z/b  O:x/d  O:x/c  O:x/c  O:x/c &&
-		test_cmp expect actual &&
+			git ls-files -s >out &&
+			test_line_count = 6 out &&
+			git ls-files -u >out &&
+			test_line_count = 3 out &&
+			git ls-files -o >out &&
+			test_line_count = 3 out &&
 
-		git hash-object y/c~B^0 >actual &&
-		git rev-parse O:x/c >expect &&
-		test_cmp expect actual &&
+			git rev-parse >actual \
+				:0:y/a :0:y/b :0:x/d :1:x/c :2:w/c :3:y/c &&
+			git rev-parse >expect \
+				 O:z/a  O:z/b  O:x/d  O:x/c  O:x/c  O:x/c &&
+			test_cmp expect actual &&
+
+			git hash-object y/c~B^0 >actual &&
+			git rev-parse O:x/c >expect &&
+			test_cmp expect actual
+		fi &&
 
 		echo important >expect &&
 		test_cmp expect y/c
@@ -3326,25 +3425,38 @@ test_expect_success '10c2: Overwrite untracked with dir rename/rename(1to2), oth
 		echo important >y/c &&
 
 		test_must_fail git -c merge.directoryRenames=true merge -s recursive A^0 >out 2>err &&
-		test_i18ngrep "CONFLICT (rename/rename)" out &&
-		test_i18ngrep "Refusing to lose untracked file at y/c; adding as y/c~HEAD instead" out &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			test_path_is_missing .git/MERGE_HEAD &&
+			test_i18ngrep "error: The following untracked working tree files would be overwritten by merge" err &&
 
-		git ls-files -s >out &&
-		test_line_count = 6 out &&
-		git ls-files -u >out &&
-		test_line_count = 3 out &&
-		git ls-files -o >out &&
-		test_line_count = 3 out &&
+			git ls-files -s >out &&
+			test_line_count = 4 out &&
+			git ls-files -u >out &&
+			test_line_count = 0 out &&
+			git ls-files -o >out &&
+			test_line_count = 3 out
+		else
+			test_i18ngrep "CONFLICT (rename/rename)" out &&
+			test_i18ngrep "Refusing to lose untracked file at y/c; adding as y/c~HEAD instead" out &&
 
-		git rev-parse >actual \
-			:0:y/a :0:y/b :0:x/d :1:x/c :3:w/c :2:y/c &&
-		git rev-parse >expect \
-			 O:z/a  O:z/b  O:x/d  O:x/c  O:x/c  O:x/c &&
-		test_cmp expect actual &&
+			git ls-files -s >out &&
+			test_line_count = 6 out &&
+			git ls-files -u >out &&
+			test_line_count = 3 out &&
+			git ls-files -o >out &&
+			test_line_count = 3 out &&
 
-		git hash-object y/c~HEAD >actual &&
-		git rev-parse O:x/c >expect &&
-		test_cmp expect actual &&
+			git rev-parse >actual \
+				:0:y/a :0:y/b :0:x/d :1:x/c :3:w/c :2:y/c &&
+			git rev-parse >expect \
+				 O:z/a  O:z/b  O:x/d  O:x/c  O:x/c  O:x/c &&
+			test_cmp expect actual &&
+
+			git hash-object y/c~HEAD >actual &&
+			git rev-parse O:x/c >expect &&
+			test_cmp expect actual
+		fi &&
 
 		echo important >expect &&
 		test_cmp expect y/c
@@ -3402,37 +3514,50 @@ test_expect_success '10d: Delete untracked with dir rename/rename(2to1)' '
 		echo important >y/wham &&
 
 		test_must_fail git -c merge.directoryRenames=true merge -s recursive B^0 >out 2>err &&
-		test_i18ngrep "CONFLICT (rename/rename)" out &&
-		test_i18ngrep "Refusing to lose untracked file at y/wham" out &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			test_path_is_missing .git/MERGE_HEAD &&
+			test_i18ngrep "error: The following untracked working tree files would be overwritten by merge" err &&
 
-		git ls-files -s >out &&
-		test_line_count = 6 out &&
-		git ls-files -u >out &&
-		test_line_count = 2 out &&
-		git ls-files -o >out &&
-		test_line_count = 3 out &&
+			git ls-files -s >out &&
+			test_line_count = 6 out &&
+			git ls-files -u >out &&
+			test_line_count = 0 out &&
+			git ls-files -o >out &&
+			test_line_count = 3 out
+		else
+			test_i18ngrep "CONFLICT (rename/rename)" out &&
+			test_i18ngrep "Refusing to lose untracked file at y/wham" out &&
 
-		git rev-parse >actual \
-			:0:y/a :0:y/b :0:y/d :0:y/e :2:y/wham :3:y/wham &&
-		git rev-parse >expect \
-			 O:z/a  O:z/b  O:x/d  O:x/e  O:z/c     O:x/f &&
-		test_cmp expect actual &&
+			git ls-files -s >out &&
+			test_line_count = 6 out &&
+			git ls-files -u >out &&
+			test_line_count = 2 out &&
+			git ls-files -o >out &&
+			test_line_count = 3 out &&
 
-		test_must_fail git rev-parse :1:y/wham &&
+			git rev-parse >actual \
+				:0:y/a :0:y/b :0:y/d :0:y/e :2:y/wham :3:y/wham &&
+			git rev-parse >expect \
+				 O:z/a  O:z/b  O:x/d  O:x/e  O:z/c     O:x/f &&
+			test_cmp expect actual &&
+
+			test_must_fail git rev-parse :1:y/wham &&
+
+			# Test that two-way merge in y/wham~merged is as expected
+			git cat-file -p :2:y/wham >expect &&
+			git cat-file -p :3:y/wham >other &&
+			>empty &&
+			test_must_fail git merge-file \
+				-L "HEAD" \
+				-L "" \
+				-L "B^0" \
+				expect empty other &&
+			test_cmp expect y/wham~merged
+		fi &&
 
 		echo important >expect &&
-		test_cmp expect y/wham &&
-
-		# Test that the two-way merge in y/wham~merged is as expected
-		git cat-file -p :2:y/wham >expect &&
-		git cat-file -p :3:y/wham >other &&
-		>empty &&
-		test_must_fail git merge-file \
-			-L "HEAD" \
-			-L "" \
-			-L "B^0" \
-			expect empty other &&
-		test_cmp expect y/wham~merged
+		test_cmp expect y/wham
 	)
 '
 
@@ -3471,7 +3596,7 @@ test_setup_10e () {
 	)
 }
 
-test_expect_failure '10e: Does git complain about untracked file that is not really in the way?' '
+test_expect_merge_algorithm failure success '10e: Does git complain about untracked file that is not really in the way?' '
 	test_setup_10e &&
 	(
 		cd 10e &&
@@ -3562,28 +3687,35 @@ test_expect_success '11a: Avoid losing dirty contents with simple rename' '
 		echo stuff >>z/c &&
 
 		test_must_fail git -c merge.directoryRenames=true merge -s recursive B^0 >out 2>err &&
-		test_i18ngrep "Refusing to lose dirty file at z/c" out &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			test_path_is_missing .git/MERGE_HEAD &&
+			test_i18ngrep "error: Your local changes to the following files would be overwritten by merge" err
+		else
+			test_i18ngrep "Refusing to lose dirty file at z/c" out &&
+
+			git ls-files -s >out &&
+			test_line_count = 2 out &&
+			git ls-files -u >out &&
+			test_line_count = 1 out &&
+			git ls-files -o >out &&
+			test_line_count = 3 out &&
+
+			git rev-parse >actual \
+				:0:z/a :2:z/c &&
+			git rev-parse >expect \
+				 O:z/a  B:z/b &&
+			test_cmp expect actual &&
+
+			git hash-object z/c~HEAD >actual &&
+			git rev-parse B:z/b >expect &&
+			test_cmp expect actual
+		fi &&
 
 		test_seq 1 10 >expected &&
 		echo stuff >>expected &&
-		test_cmp expected z/c &&
+		test_cmp expected z/c
 
-		git ls-files -s >out &&
-		test_line_count = 2 out &&
-		git ls-files -u >out &&
-		test_line_count = 1 out &&
-		git ls-files -o >out &&
-		test_line_count = 4 out &&
-
-		git rev-parse >actual \
-			:0:z/a :2:z/c &&
-		git rev-parse >expect \
-			 O:z/a  B:z/b &&
-		test_cmp expect actual &&
-
-		git hash-object z/c~HEAD >actual &&
-		git rev-parse B:z/b >expect &&
-		test_cmp expect actual
 	)
 '
 
@@ -3634,32 +3766,39 @@ test_expect_success '11b: Avoid losing dirty file involved in directory rename'
 		git checkout A^0 &&
 		echo stuff >>z/c &&
 
-		git -c merge.directoryRenames=true merge -s recursive B^0 >out 2>err &&
-		test_i18ngrep "Refusing to lose dirty file at z/c" out &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			test_must_fail git -c merge.directoryRenames=true merge -s recursive B^0 >out 2>err &&
+			test_path_is_missing .git/MERGE_HEAD &&
+			test_i18ngrep "error: Your local changes to the following files would be overwritten by merge" err
+		else
+			git -c merge.directoryRenames=true merge -s recursive B^0 >out 2>err &&
+			test_i18ngrep "Refusing to lose dirty file at z/c" out &&
+
+			git ls-files -s >out &&
+			test_line_count = 3 out &&
+			git ls-files -u >out &&
+			test_line_count = 0 out &&
+			git ls-files -m >out &&
+			test_line_count = 0 out &&
+			git ls-files -o >out &&
+			test_line_count = 3 out &&
+
+			git rev-parse >actual \
+				:0:x/b :0:y/a :0:y/c &&
+			git rev-parse >expect \
+				 O:x/b  O:z/a  B:x/c &&
+			test_cmp expect actual &&
+
+			git hash-object y/c >actual &&
+			git rev-parse B:x/c >expect &&
+			test_cmp expect actual
+		fi &&
 
 		grep -q stuff z/c &&
 		test_seq 1 10 >expected &&
 		echo stuff >>expected &&
-		test_cmp expected z/c &&
-
-		git ls-files -s >out &&
-		test_line_count = 3 out &&
-		git ls-files -u >out &&
-		test_line_count = 0 out &&
-		git ls-files -m >out &&
-		test_line_count = 0 out &&
-		git ls-files -o >out &&
-		test_line_count = 4 out &&
-
-		git rev-parse >actual \
-			:0:x/b :0:y/a :0:y/c &&
-		git rev-parse >expect \
-			 O:x/b  O:z/a  B:x/c &&
-		test_cmp expect actual &&
-
-		git hash-object y/c >actual &&
-		git rev-parse B:x/c >expect &&
-		test_cmp expect actual
+		test_cmp expected z/c
 	)
 '
 
@@ -3711,7 +3850,13 @@ test_expect_success '11c: Avoid losing not-uptodate with rename + D/F conflict'
 		echo stuff >>y/c &&
 
 		test_must_fail git -c merge.directoryRenames=true merge -s recursive B^0 >out 2>err &&
-		test_i18ngrep "following files would be overwritten by merge" err &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			test_path_is_missing .git/MERGE_HEAD &&
+			test_i18ngrep "error: Your local changes to the following files would be overwritten by merge" err
+		else
+			test_i18ngrep "following files would be overwritten by merge" err
+		fi &&
 
 		grep -q stuff y/c &&
 		test_seq 1 10 >expected &&
@@ -3779,29 +3924,35 @@ test_expect_success '11d: Avoid losing not-uptodate with rename + D/F conflict'
 		echo stuff >>z/c &&
 
 		test_must_fail git -c merge.directoryRenames=true merge -s recursive B^0 >out 2>err &&
-		test_i18ngrep "Refusing to lose dirty file at z/c" out &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			test_path_is_missing .git/MERGE_HEAD &&
+			test_i18ngrep "error: Your local changes to the following files would be overwritten by merge" err
+		else
+			test_i18ngrep "Refusing to lose dirty file at z/c" out &&
+
+			git ls-files -s >out &&
+			test_line_count = 4 out &&
+			git ls-files -u >out &&
+			test_line_count = 1 out &&
+			git ls-files -o >out &&
+			test_line_count = 4 out &&
+
+			git rev-parse >actual \
+				:0:x/b :0:y/a :0:y/c/d :3:y/c &&
+			git rev-parse >expect \
+				 O:x/b  O:z/a  B:y/c/d  B:x/c &&
+			test_cmp expect actual &&
+
+			git hash-object y/c~HEAD >actual &&
+			git rev-parse B:x/c >expect &&
+			test_cmp expect actual
+		fi &&
 
 		grep -q stuff z/c &&
 		test_seq 1 10 >expected &&
 		echo stuff >>expected &&
-		test_cmp expected z/c &&
-
-		git ls-files -s >out &&
-		test_line_count = 4 out &&
-		git ls-files -u >out &&
-		test_line_count = 1 out &&
-		git ls-files -o >out &&
-		test_line_count = 5 out &&
-
-		git rev-parse >actual \
-			:0:x/b :0:y/a :0:y/c/d :3:y/c &&
-		git rev-parse >expect \
-			 O:x/b  O:z/a  B:y/c/d  B:x/c &&
-		test_cmp expect actual &&
-
-		git hash-object y/c~HEAD >actual &&
-		git rev-parse B:x/c >expect &&
-		test_cmp expect actual
+		test_cmp expected z/c
 	)
 '
 
@@ -3859,37 +4010,43 @@ test_expect_success '11e: Avoid deleting not-uptodate with dir rename/rename(1to
 		echo mods >>y/c &&
 
 		test_must_fail git -c merge.directoryRenames=true merge -s recursive B^0 >out 2>err &&
-		test_i18ngrep "CONFLICT (rename/rename)" out &&
-		test_i18ngrep "Refusing to lose dirty file at y/c" out &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			test_path_is_missing .git/MERGE_HEAD &&
+			test_i18ngrep "error: Your local changes to the following files would be overwritten by merge" err
+		else
+			test_i18ngrep "CONFLICT (rename/rename)" out &&
+			test_i18ngrep "Refusing to lose dirty file at y/c" out &&
 
-		git ls-files -s >out &&
-		test_line_count = 7 out &&
-		git ls-files -u >out &&
-		test_line_count = 4 out &&
-		git ls-files -o >out &&
-		test_line_count = 3 out &&
+			git ls-files -s >out &&
+			test_line_count = 7 out &&
+			git ls-files -u >out &&
+			test_line_count = 4 out &&
+			git ls-files -o >out &&
+			test_line_count = 3 out &&
+
+			git rev-parse >actual \
+				:0:y/a :0:y/b :0:x/d :1:x/c :2:w/c :2:y/c :3:y/c &&
+			git rev-parse >expect \
+				 O:z/a  O:z/b  O:x/d  O:x/c  O:x/c  A:y/c  O:x/c &&
+			test_cmp expect actual &&
+
+			# See if y/c~merged has expected contents; requires manually
+			# doing the expected file merge
+			git cat-file -p A:y/c >c1 &&
+			git cat-file -p B:z/c >c2 &&
+			>empty &&
+			test_must_fail git merge-file \
+				-L "HEAD" \
+				-L "" \
+				-L "B^0" \
+				c1 empty c2 &&
+			test_cmp c1 y/c~merged
+		fi &&
 
 		echo different >expected &&
 		echo mods >>expected &&
-		test_cmp expected y/c &&
-
-		git rev-parse >actual \
-			:0:y/a :0:y/b :0:x/d :1:x/c :2:w/c :2:y/c :3:y/c &&
-		git rev-parse >expect \
-			 O:z/a  O:z/b  O:x/d  O:x/c  O:x/c  A:y/c  O:x/c &&
-		test_cmp expect actual &&
-
-		# See if y/c~merged has expected contents; requires manually
-		# doing the expected file merge
-		git cat-file -p A:y/c >c1 &&
-		git cat-file -p B:z/c >c2 &&
-		>empty &&
-		test_must_fail git merge-file \
-			-L "HEAD" \
-			-L "" \
-			-L "B^0" \
-			c1 empty c2 &&
-		test_cmp c1 y/c~merged
+		test_cmp expected y/c
 	)
 '
 
@@ -3942,38 +4099,44 @@ test_expect_success '11f: Avoid deleting not-uptodate with dir rename/rename(2to
 		echo important >>y/wham &&
 
 		test_must_fail git -c merge.directoryRenames=true merge -s recursive B^0 >out 2>err &&
-		test_i18ngrep "CONFLICT (rename/rename)" out &&
-		test_i18ngrep "Refusing to lose dirty file at y/wham" out &&
+		if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+		then
+			test_path_is_missing .git/MERGE_HEAD &&
+			test_i18ngrep "error: Your local changes to the following files would be overwritten by merge" err
+		else
+			test_i18ngrep "CONFLICT (rename/rename)" out &&
+			test_i18ngrep "Refusing to lose dirty file at y/wham" out &&
 
-		git ls-files -s >out &&
-		test_line_count = 4 out &&
-		git ls-files -u >out &&
-		test_line_count = 2 out &&
-		git ls-files -o >out &&
-		test_line_count = 3 out &&
+			git ls-files -s >out &&
+			test_line_count = 4 out &&
+			git ls-files -u >out &&
+			test_line_count = 2 out &&
+			git ls-files -o >out &&
+			test_line_count = 3 out &&
+
+			test_must_fail git rev-parse :1:y/wham &&
+
+			git rev-parse >actual \
+				:0:y/a :0:y/b :2:y/wham :3:y/wham &&
+			git rev-parse >expect \
+				 O:z/a  O:z/b  O:x/c     O:x/d &&
+			test_cmp expect actual &&
+
+			# Test that two-way merge in y/wham~merged is as expected
+			git cat-file -p :2:y/wham >expect &&
+			git cat-file -p :3:y/wham >other &&
+			>empty &&
+			test_must_fail git merge-file \
+				-L "HEAD" \
+				-L "" \
+				-L "B^0" \
+				expect empty other &&
+			test_cmp expect y/wham~merged
+		fi &&
 
 		test_seq 1 10 >expected &&
 		echo important >>expected &&
-		test_cmp expected y/wham &&
-
-		test_must_fail git rev-parse :1:y/wham &&
-
-		git rev-parse >actual \
-			:0:y/a :0:y/b :2:y/wham :3:y/wham &&
-		git rev-parse >expect \
-			 O:z/a  O:z/b  O:x/c     O:x/d &&
-		test_cmp expect actual &&
-
-		# Test that the two-way merge in y/wham~merged is as expected
-		git cat-file -p :2:y/wham >expect &&
-		git cat-file -p :3:y/wham >other &&
-		>empty &&
-		test_must_fail git merge-file \
-			-L "HEAD" \
-			-L "" \
-			-L "B^0" \
-			expect empty other &&
-		test_cmp expect y/wham~merged
+		test_cmp expected y/wham
 	)
 '
 
@@ -4104,7 +4267,7 @@ test_setup_12b1 () {
 	)
 }
 
-test_expect_failure '12b1: Moving two directory hierarchies into each other' '
+test_expect_merge_algorithm failure success '12b1: Moving two directory hierarchies into each other' '
 	test_setup_12b1 &&
 	(
 		cd 12b1 &&
@@ -4272,7 +4435,7 @@ test_setup_12c1 () {
 	)
 }
 
-test_expect_failure '12c1: Moving one directory hierarchy into another w/ content merge' '
+test_expect_merge_algorithm failure success '12c1: Moving one directory hierarchy into another w/ content merge' '
 	test_setup_12c1 &&
 	(
 		cd 12c1 &&
@@ -4562,20 +4725,22 @@ test_expect_success '12e: Rename/merge subdir into the root, variant 2' '
 #              folder/subdir/newsubdir/e_Merge2
 #              folder/subdir/tweaked/{h,Makefile_SUB_Merge1,newfile.py}
 #              folder/unchanged/<LOTS OF FILES>
-#
-# Notes: This testcase happens to exercise lots of the
-#        optimization-specific codepaths in merge-ort, and also
-#        demonstrated a failing of the directory rename detection algorithm
-#        in merge-recursive; newfile.c should not get pushed into
-#        folder/subdir/newsubdir/, yet merge-recursive put it there because
-#        the rename of dir/subdir/{a,b,c,d} -> folder/subdir/{a,b,c,d}
-#        looks like
-#            dir/ -> folder/,
-#        whereas the rename of dir/subdir/e -> folder/subdir/newsubdir/e
-#        looks like
-#            dir/subdir/ -> folder/subdir/newsubdir/
-#        and if we note that newfile.c is found in dir/subdir/, we might
-#        overlook the dir/ -> folder/ rule that has more weight.
+# Things being checked here:
+#   1. dir/subdir/newfile.c does not get pushed into folder/subdir/newsubdir/.
+#      dir/subdir/{a,b,c,d} -> folder/subdir/{a,b,c,d} looks like
+#          dir/ -> folder/,
+#      whereas dir/subdir/e -> folder/subdir/newsubdir/e looks like
+#          dir/subdir/ -> folder/subdir/newsubdir/
+#      and if we note that newfile.c is found in dir/subdir/, we might overlook
+#      the dir/ -> folder/ rule that has more weight.  Older git versions did
+#      this.
+#   2. The code to do trivial directory resolves.  Note that
+#      dir/subdir/unchanged/ is unchanged and can be deleted, and files in the
+#      new folder/subdir/unchanged/ are not needed as a target to any renames.
+#      Thus, in the second collect_merge_info_callback() we can just resolve
+#      these two directories trivially without recursing.)
+#   3. Exercising the codepaths for caching renames and deletes from one cherry
+#      pick and re-applying them in the subsequent one.
 
 test_setup_12f () {
 	test_create_repo 12f &&
@@ -4632,7 +4797,7 @@ test_setup_12f () {
 	)
 }
 
-test_expect_failure '12f: Trivial directory resolve, caching, all kinds of fun' '
+test_expect_merge_algorithm failure success '12f: Trivial directory resolve, caching, all kinds of fun' '
 	test_setup_12f &&
 	(
 		cd 12f &&
@@ -4640,7 +4805,7 @@ test_expect_failure '12f: Trivial directory resolve, caching, all kinds of fun'
 		git checkout A^0 &&
 		git branch Bmod B &&
 
-		git -c merge.directoryRenames=true rebase A Bmod &&
+		GIT_TRACE2_PERF="$(pwd)/trace.output" git -c merge.directoryRenames=true rebase A Bmod &&
 
 		echo Checking the pick of B1... &&
 
@@ -4721,7 +4886,12 @@ test_expect_failure '12f: Trivial directory resolve, caching, all kinds of fun'
 		test_seq  2 12 >e_Merge2 &&
 		git hash-object e_Merge2 >expect &&
 		git rev-parse Bmod:folder/subdir/newsubdir/e >actual &&
-		test_cmp expect actual
+		test_cmp expect actual &&
+
+		grep region_enter.*collect_merge_info trace.output >collect &&
+		test_line_count = 4 collect &&
+		grep region_enter.*process_entries$ trace.output >process &&
+		test_line_count = 2 process
 	)
 '
 
diff --git a/t/t6426-merge-skip-unneeded-updates.sh b/t/t6426-merge-skip-unneeded-updates.sh
index 699813671c..d7eeee4310 100755
--- a/t/t6426-merge-skip-unneeded-updates.sh
+++ b/t/t6426-merge-skip-unneeded-updates.sh
@@ -23,6 +23,7 @@ test_description="merge cases"
 #                     files that might be renamed into each other's paths.)
 
 . ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-merge.sh
 
 
 ###########################################################################
@@ -666,7 +667,7 @@ test_setup_4a () {
 #   correct requires doing the merge in-memory first, then realizing that no
 #   updates to the file are necessary, and thus that we can just leave the path
 #   alone.
-test_expect_failure '4a: Change on A, change on B subset of A, dirty mods present' '
+test_expect_merge_algorithm failure success '4a: Change on A, change on B subset of A, dirty mods present' '
 	test_setup_4a &&
 	(
 		cd 4a &&
diff --git a/t/t6430-merge-recursive.sh b/t/t6430-merge-recursive.sh
index a328260d42..9c08e63af2 100755
--- a/t/t6430-merge-recursive.sh
+++ b/t/t6430-merge-recursive.sh
@@ -3,6 +3,7 @@
 test_description='merge-recursive backend test'
 
 . ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-merge.sh
 
 test_expect_success 'setup 1' '
 
@@ -641,7 +642,7 @@ test_expect_success 'merge-recursive copy vs. rename' '
 	test_cmp expected actual
 '
 
-test_expect_failure 'merge-recursive rename vs. rename/symlink' '
+test_expect_merge_algorithm failure success 'merge-recursive rename vs. rename/symlink' '
 
 	git checkout -f rename &&
 	git merge rename-ln &&
diff --git a/t/t6436-merge-overwrite.sh b/t/t6436-merge-overwrite.sh
index dd8ab7ede1..dd9376842f 100755
--- a/t/t6436-merge-overwrite.sh
+++ b/t/t6436-merge-overwrite.sh
@@ -97,11 +97,19 @@ test_expect_success 'will not overwrite unstaged changes in renamed file' '
 	git mv c1.c other.c &&
 	git commit -m rename &&
 	cp important other.c &&
-	test_must_fail git merge c1a >out &&
-	test_i18ngrep "Refusing to lose dirty file at other.c" out &&
-	test_path_is_file other.c~HEAD &&
-	test $(git hash-object other.c~HEAD) = $(git rev-parse c1a:c1.c) &&
-	test_cmp important other.c
+	if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	then
+		test_must_fail git merge c1a >out 2>err &&
+		test_i18ngrep "would be overwritten by merge" err &&
+		test_cmp important other.c &&
+		test_path_is_missing .git/MERGE_HEAD
+	else
+		test_must_fail git merge c1a >out &&
+		test_i18ngrep "Refusing to lose dirty file at other.c" out &&
+		test_path_is_file other.c~HEAD &&
+		test $(git hash-object other.c~HEAD) = $(git rev-parse c1a:c1.c) &&
+		test_cmp important other.c
+	fi
 '
 
 test_expect_success 'will not overwrite untracked subtree' '
diff --git a/t/t6437-submodule-merge.sh b/t/t6437-submodule-merge.sh
index 6a1e5f8232..3ead2b726f 100755
--- a/t/t6437-submodule-merge.sh
+++ b/t/t6437-submodule-merge.sh
@@ -127,7 +127,12 @@ test_expect_success 'merging should conflict for non fast-forward' '
 	 git checkout -b test-nonforward b &&
 	 (cd sub &&
 	  git rev-parse sub-d > ../expect) &&
-	 test_must_fail git merge c 2> actual  &&
+	  if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	  then
+		test_must_fail git merge c >actual
+	  else
+		test_must_fail git merge c 2> actual
+	  fi &&
 	 grep $(cat expect) actual > /dev/null &&
 	 git reset --hard)
 '
@@ -138,9 +143,21 @@ test_expect_success 'merging should fail for ambiguous common parent' '
 	(cd sub &&
 	 git checkout -b ambiguous sub-b &&
 	 git merge sub-c &&
-	 git rev-parse sub-d > ../expect1 &&
-	 git rev-parse ambiguous > ../expect2) &&
-	test_must_fail git merge c 2> actual &&
+	 if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	 then
+		git rev-parse --short sub-d >../expect1 &&
+		git rev-parse --short ambiguous >../expect2
+	 else
+		git rev-parse sub-d > ../expect1 &&
+		git rev-parse ambiguous > ../expect2
+	 fi
+	 ) &&
+	 if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	 then
+		test_must_fail git merge c >actual
+	 else
+		test_must_fail git merge c 2> actual
+	 fi &&
 	grep $(cat expect1) actual > /dev/null &&
 	grep $(cat expect2) actual > /dev/null &&
 	git reset --hard)
diff --git a/t/t7602-merge-octopus-many.sh b/t/t7602-merge-octopus-many.sh
index 6abe441ae3..13859ec859 100755
--- a/t/t7602-merge-octopus-many.sh
+++ b/t/t7602-merge-octopus-many.sh
@@ -77,6 +77,12 @@ Merge made by the 'recursive' strategy.
 EOF
 
 test_expect_success 'merge reduces irrelevant remote heads' '
+	if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	then
+		mv expected expected.tmp &&
+		sed s/recursive/ort/ expected.tmp >expected &&
+		rm expected.tmp
+	fi &&
 	GIT_MERGE_VERBOSITY=0 git merge c4 c5 >actual &&
 	test_i18ncmp expected actual
 '
diff --git a/t/t7610-mergetool.sh b/t/t7610-mergetool.sh
index ad288ddc69..70afdd06fa 100755
--- a/t/t7610-mergetool.sh
+++ b/t/t7610-mergetool.sh
@@ -532,7 +532,14 @@ test_expect_success 'file vs modified submodule' '
 	yes "" | git mergetool file1 file2 spaced\ name subdir/file3 &&
 	yes "" | git mergetool both &&
 	yes "d" | git mergetool file11 file12 &&
-	yes "l" | git mergetool submod &&
+	if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	then
+		yes "c" | git mergetool submod~HEAD &&
+		git rm submod &&
+		git mv submod~HEAD submod
+	else
+		yes "l" | git mergetool submod
+	fi &&
 	git submodule update -N &&
 	echo "not a submodule" >expect &&
 	test_cmp expect submod &&
@@ -549,7 +556,15 @@ test_expect_success 'file vs modified submodule' '
 	yes "" | git mergetool file1 file2 spaced\ name subdir/file3 &&
 	yes "" | git mergetool both &&
 	yes "d" | git mergetool file11 file12 &&
-	yes "r" | git mergetool submod &&
+	if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	then
+		mv submod submod.orig &&
+		git rm --cached submod &&
+		yes "c" | git mergetool submod~test19 &&
+		git mv submod~test19 submod
+	else
+		yes "r" | git mergetool submod
+	fi &&
 	test -d submod.orig &&
 	git submodule update -N &&
 	echo "not a submodule" >expect &&
@@ -567,6 +582,10 @@ test_expect_success 'file vs modified submodule' '
 	yes "" | git mergetool both &&
 	yes "d" | git mergetool file11 file12 &&
 	yes "l" | git mergetool submod &&
+	if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	then
+		yes "d" | git mergetool submod~test19
+	fi &&
 	echo "master submodule" >expect &&
 	test_cmp expect submod/bar &&
 	git submodule update -N &&
@@ -664,7 +683,14 @@ test_expect_success 'directory vs modified submodule' '
 	test_must_fail git merge master &&
 	test -n "$(git ls-files -u)" &&
 	test ! -e submod.orig &&
-	yes "r" | git mergetool submod &&
+	if test "$GIT_TEST_MERGE_ALGORITHM" = ort
+	then
+		yes "r" | git mergetool submod~master &&
+		git mv submod submod.orig &&
+		git mv submod~master submod
+	else
+		yes "r" | git mergetool submod
+	fi &&
 	test -d submod.orig &&
 	echo "not a submodule" >expect &&
 	test_cmp expect submod.orig/file16 &&