[analysis] Implement a Bool lattice (#6036)

This is a lattice with two elements: `false` is bottom and `true` is top.

Add a new gtest file for testing lattices.

src/analysis/lattices/bool.h

@@ -0,0 +1,47 @@
+/*
+ * 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.
+ */
+
+#ifndef wasm_analysis_lattices_bool_h
+#define wasm_analysis_lattices_bool_h
+
+#include "../lattice.h"
+
+namespace wasm::analysis {
+
+// A lattice with two elements: the top element is `true` and the bottom element
+// is `false`.
+struct Bool {
+  using Element = bool;
+  Element getBottom() const noexcept { return false; }
+  LatticeComparison compare(Element a, Element b) const noexcept {
+    return a > b ? GREATER : a == b ? EQUAL : LESS;
+  }
+  bool join(Element& self, Element other) const noexcept {
+    if (!self && other) {
+      self = other;
+      return true;
+    }
+    return false;
+  }
+};
+
+#if __cplusplus >= 202002L
+static_assert(Lattice<Bool>);
+#endif // __cplusplus >= 202002L
+
+} // namespace wasm::analysis
+
+#endif // wasm_analysis_lattices_bool_h

test/gtest/CMakeLists.txt

@@ -4,6 +4,7 @@ include_directories(../../src/wasm)
 set(unittest_SOURCES
   cfg.cpp
   dfa_minimization.cpp
+  lattices.cpp
   possible-contents.cpp
   printing.cpp
   stringify.cpp

test/gtest/lattices.cpp

@@ -0,0 +1,50 @@
+/*
+ * 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 "analysis/lattices/bool.h"
+#include "gtest/gtest.h"
+
+using namespace wasm;
+
+TEST(BoolLattice, GetBottom) {
+  analysis::Bool lattice;
+  EXPECT_FALSE(lattice.getBottom());
+}
+
+TEST(BoolLattice, Compare) {
+  analysis::Bool lattice;
+  EXPECT_EQ(lattice.compare(false, false), analysis::EQUAL);
+  EXPECT_EQ(lattice.compare(false, true), analysis::LESS);
+  EXPECT_EQ(lattice.compare(true, false), analysis::GREATER);
+  EXPECT_EQ(lattice.compare(true, true), analysis::EQUAL);
+}
+
+TEST(BoolLattice, Join) {
+  analysis::Bool lattice;
+  bool elem = false;
+
+  EXPECT_FALSE(lattice.join(elem, false));
+  ASSERT_FALSE(elem);
+
+  EXPECT_TRUE(lattice.join(elem, true));
+  ASSERT_TRUE(elem);
+
+  EXPECT_FALSE(lattice.join(elem, false));
+  ASSERT_TRUE(elem);
+
+  EXPECT_FALSE(lattice.join(elem, true));
+  ASSERT_TRUE(elem);
+}