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+/*
+ * Copyright 2021 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_ir_lubs_h
+#define wasm_ir_lubs_h
+
+#include "ir/module-utils.h"
+#include "wasm.h"
+
+namespace wasm {
+
+// Helper to find a LUB of a series of expressions. This works incrementally so
+// that if we see we are not improving on an existing type then we can stop
+// early.
+struct LUBFinder {
+  // The least upper bound we found so far.
+  Type lub = Type::unreachable;
+
+  // Note another type to take into account in the lub. Returns the new lub.
+  Type note(Type type) { return lub = Type::getLeastUpperBound(lub, type); }
+
+  Type note(Expression* curr) { return note(curr->type); }
+
+  // Returns whether we noted any (reachable) value.
+  bool noted() { return lub != Type::unreachable; }
+
+  // Returns the lub that we found.
+  Type get() { return lub; }
+};
+
+} // namespace wasm
+
+#endif // wasm_ir_lubs_h