Add sign to idempotent ops list

Author: ananyamukh6

onnxoptimizer/passes/eliminate_consecutive_idempotent_ops.h

@@ -24,7 +24,7 @@ struct EliminateConsecutiveIdempotentOps final : public PredicateBasedPass {
 
   bool patternMatchPredicate(Node* node) override {
     static const std::unordered_set<std::string> idempotent_ops = {
-        "Ceil", "Floor", "Round", "Relu", "Reshape"};
+        "Ceil", "Floor", "Round", "Relu", "Reshape", "Sign"};
     for (const auto& op : idempotent_ops) {
       // TODO: support uses().size() > 1 for ops except Reshape
       if (CheckKind(node, Symbol(op), 0, Symbol(op)) &&

onnxoptimizer/test/optimizer_test.py

@@ -4597,6 +4597,25 @@ def test_eliminate_consecutive_idempotent_op(self):
         assert optimized_model.graph.node[0].op_type == "Constant"
         assert optimized_model.graph.node[1].op_type == "Reshape"
 
+    def test_eliminate_consecutive_idempotent_sign_op(self):
+        model = parser.parse_model("""
+                <
+                    ir_version: 7,
+                    opset_import:["": 11]
+                >
+               agraph (float[1, 2, 3] X) => (float[1, 2, 3] Z)
+               {
+                  T1 = Sign(X)
+                  T2 = Sign(T1)
+                  T3 = Sign(T2)
+                  Z = Sign(T3)
+               }
+            """)
+
+        optimized_model = self._optimized(
+            model, ['eliminate_consecutive_idempotent_ops', 'eliminate_deadend'], True) 
+        assert len(optimized_model.graph.node) == 1
+        assert optimized_model.graph.node[0].op_type == "Sign"
 
 if __name__ == "__main__":
     unittest.main()