Add Valmari-Lehtinen DFA minimization as a standalone utility (#5430)

We used to have this algorithm in wasm-type.cpp, where we used it to implement equirecursive type canonicalization, but we removed it when we removed equirecursive typing. Bring the algorithm back as a standalone utility for future use in optimization passes. In particular, it will be useful in TypeMerging for identifying the greatest fixed point of mergeable types rather than the smallest fixed point.
author: Thomas Lively <tlively@google.com> 2023-01-17 11:35:23 -0600
committer: GitHub <noreply@github.com> 2023-01-17 09:35:23 -0800
commit: eedb2fe5e37174acba69e84e8bb9ee2628e0d7f3 (patch)
tree: 689c4c6a2c1a735a991013cb02c1f4bd542b0e1c /test/gtest/dfa_minimization.cpp
parent: e9012347476a9cb26f829aa9a9a8b04db3438765 (diff)
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diff --git a/test/gtest/dfa_minimization.cpp b/test/gtest/dfa_minimization.cpp
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+/*
+ * Copyright 2023 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 <set>
+#include <string>
+#include <vector>
+
+#include "support/dfa_minimization.h"
+#include "gtest/gtest.h"
+
+using namespace wasm;
+
+using State = DFA::State<std::string>;
+using Graph = std::vector<std::vector<State>>;
+using Results = std::vector<std::vector<std::string>>;
+using SetResults = std::set<std::set<std::string>>;
+
+// We don't care about order between or within the output partitions.
+SetResults settify(const Results& vecs) {
+  SetResults sets;
+  for (const auto& vec : vecs) {
+    sets.emplace(vec.begin(), vec.end());
+  }
+  return sets;
+}
+
+// Check that the same values appear in the input and output and that each value
+// appears once.
+void validate(const Graph& graph, const Results& results) {
+  std::set<std::string> inputVals;
+  for (const auto& partition : graph) {
+    for (const auto& state : partition) {
+      bool inserted = inputVals.insert(state.val).second;
+      ASSERT_TRUE(inserted);
+    }
+  }
+
+  std::set<std::string> outputVals;
+  for (const auto& partition : results) {
+    for (const auto& val : partition) {
+      ASSERT_NE(inputVals.find(val), inputVals.end());
+      ASSERT_TRUE(outputVals.insert(val).second);
+    }
+  }
+
+  ASSERT_EQ(outputVals.size(), inputVals.size());
+}
+
+TEST(DFATest, Empty) {
+  Graph graph = {};
+  auto results = DFA::refinePartitions(graph);
+  validate(graph, results);
+  EXPECT_EQ(settify(results), SetResults{});
+}
+
+TEST(DFATest, Singleton) {
+  Graph graph = {{{"A", {}}}};
+  auto results = DFA::refinePartitions(graph);
+  validate(graph, results);
+  EXPECT_EQ(settify(results), SetResults{{"A"}});
+}
+
+TEST(DFATest, CyclePartitioned) {
+  // The partitions are already maximally refined, so shouldn't change.
+  State a{"A", {"B"}};
+  State b{"B", {"C"}};
+  State c{"C", {"A"}};
+  Graph graph = {{a}, {b}, {c}};
+  auto results = DFA::refinePartitions(graph);
+  validate(graph, results);
+  EXPECT_EQ(settify(results), (SetResults{{"A"}, {"B"}, {"C"}}));
+}
+
+TEST(DFATest, CycleGrouped) {
+  // All the states are identical, so the the partition shouldn't change.
+  State a{"A", {"B"}};
+  State b{"B", {"C"}};
+  State c{"C", {"A"}};
+  Graph graph = {{a, b, c}};
+  auto results = DFA::refinePartitions(graph);
+  validate(graph, results);
+  EXPECT_EQ(settify(results), (SetResults{{"A", "B", "C"}}));
+}
+
+TEST(DFATest, CycleRefined) {
+  // A and B are distinguishable, so the partitions should be refined.
+  State a{"A", {"B"}};
+  State b{"B", {"C"}};
+  State c{"C", {"A"}};
+  Graph graph = {{a, b}, {c}};
+  auto results = DFA::refinePartitions(graph);
+  validate(graph, results);
+  EXPECT_EQ(settify(results), (SetResults{{"A"}, {"B"}, {"C"}}));
+}
+
+TEST(DFATest, ChainZip) {
+  // Chain A->B->C->D is identical to chain W->X->Y->Z.
+  State a{"A", {"B"}}, w{"W", {"X"}};
+  State b{"B", {"C"}}, x{"X", {"Y"}};
+  State c{"C", {"D"}}, y{"Y", {"Z"}};
+  State d{"D", {}}, z{"Z", {}};
+  Graph graph = {{a, b, c, d, w, x, y, z}};
+  auto results = DFA::refinePartitions(graph);
+  validate(graph, results);
+  EXPECT_EQ(settify(results),
+            (SetResults{{"A", "W"}, {"B", "X"}, {"C", "Y"}, {"D", "Z"}}));
+}
+
+TEST(DFATest, ChainUnzip) {
+  // Chain A->B->C->D looks a lot like chain W->X->Y->Z, but since Z is
+  // distinguishable, the full chains end up being separated.
+  State a{"A", {"B"}}, w{"W", {"X"}};
+  State b{"B", {"C"}}, x{"X", {"Y"}};
+  State c{"C", {"D"}}, y{"Y", {"Z"}};
+  State d{"D", {}}, z{"Z", {}};
+  Graph graph = {{a, b, c, d, w, x, y}, {z}};
+  auto results = DFA::refinePartitions(graph);
+  validate(graph, results);
+  EXPECT_EQ(
+    settify(results),
+    (SetResults{{"A"}, {"W"}, {"B"}, {"X"}, {"C"}, {"Y"}, {"D"}, {"Z"}}));
+}
author	Thomas Lively <tlively@google.com>	2023-01-17 11:35:23 -0600
committer	GitHub <noreply@github.com>	2023-01-17 09:35:23 -0800
commit	eedb2fe5e37174acba69e84e8bb9ee2628e0d7f3 (patch)
tree	689c4c6a2c1a735a991013cb02c1f4bd542b0e1c /test/gtest/dfa_minimization.cpp
parent	e9012347476a9cb26f829aa9a9a8b04db3438765 (diff)
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