Add a disjoint sets (union-find) utility (#6797)

This will be used in an upcoming type optimization pass and may be
generally useful.

2 files changed, 107 insertions, 0 deletions

diff --git a/test/gtest/CMakeLists.txt b/test/gtest/CMakeLists.txt
index 4604eea77..538ec1cdc 100644
--- a/test/gtest/CMakeLists.txt
+++ b/test/gtest/CMakeLists.txt
@@ -4,6 +4,7 @@ include_directories(../../src/wasm)
 set(unittest_SOURCES
   cfg.cpp
   dfa_minimization.cpp
+  disjoint_sets.cpp
   json.cpp
   lattices.cpp
   possible-contents.cpp
diff --git a/test/gtest/disjoint_sets.cpp b/test/gtest/disjoint_sets.cpp
new file mode 100644
index 000000000..f974957a3
--- /dev/null
+++ b/test/gtest/disjoint_sets.cpp
@@ -0,0 +1,106 @@
+/*
+ * Copyright 2024 WebAssembly Community Group participants
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "support/disjoint_sets.h"
+#include "gtest/gtest.h"
+
+using namespace wasm;
+
+TEST(DisjointSetsTest, NewSets) {
+  DisjointSets sets;
+  auto elem1 = sets.addSet();
+  auto elem2 = sets.addSet();
+  EXPECT_NE(elem1, elem2);
+
+  auto root1 = sets.getRoot(elem1);
+  EXPECT_EQ(elem1, root1);
+
+  auto root2 = sets.getRoot(elem2);
+  EXPECT_EQ(elem2, root2);
+}
+
+TEST(DisjointSetsTest, Union) {
+  DisjointSets sets;
+  auto elem1 = sets.addSet();
+  auto elem2 = sets.addSet();
+  auto root = sets.getUnion(elem1, elem2);
+  EXPECT_TRUE(root == elem1 || root == elem2);
+
+  auto root1 = sets.getRoot(elem1);
+  auto root2 = sets.getRoot(elem2);
+  EXPECT_EQ(root1, root);
+  EXPECT_EQ(root2, root);
+}
+
+TEST(DisjointSetsTest, TwoUnions) {
+  DisjointSets sets;
+  auto elem1 = sets.addSet();
+  auto elem2 = sets.addSet();
+  auto elem3 = sets.addSet();
+  auto elem4 = sets.addSet();
+
+  auto rootA = sets.getUnion(elem1, elem3);
+  auto rootB = sets.getUnion(elem2, elem4);
+  EXPECT_EQ(sets.getRoot(elem1), rootA);
+  EXPECT_EQ(sets.getRoot(elem2), rootB);
+  EXPECT_EQ(sets.getRoot(elem3), rootA);
+  EXPECT_EQ(sets.getRoot(elem4), rootB);
+  EXPECT_NE(rootA, rootB);
+}
+
+TEST(DisjointSetsTest, UnionList) {
+  constexpr size_t count = 16;
+  DisjointSets sets;
+  size_t elems[count];
+  for (size_t i = 0; i < count; ++i) {
+    elems[i] = sets.addSet();
+  }
+
+  for (size_t i = 1; i < count; ++i) {
+    sets.getUnion(elems[i], elems[i - 1]);
+  }
+
+  auto root = sets.getRoot(elems[0]);
+  for (size_t rep = 0; rep < 2; ++rep) {
+    for (size_t i = 0; i < count; ++i) {
+      auto currRoot = sets.getRoot(elems[i]);
+      EXPECT_EQ(currRoot, root);
+    }
+  }
+}
+
+TEST(DisjointSetsTest, UnionTree) {
+  constexpr size_t count = 16;
+  DisjointSets sets;
+  size_t elems[count];
+  for (size_t i = 0; i < count; ++i) {
+    elems[i] = sets.addSet();
+  }
+
+  for (size_t stride = 2; stride <= count; stride *= 2) {
+    for (size_t i = 0; i < count; i += stride) {
+      sets.getUnion(elems[i], elems[i + stride / 2]);
+    }
+  }
+
+  auto root = sets.getRoot(elems[0]);
+  for (size_t rep = 0; rep < 2; ++rep) {
+    for (size_t i = 0; i < count; ++i) {
+      auto currRoot = sets.getRoot(elems[i]);
+      EXPECT_EQ(currRoot, root);
+    }
+  }
+}