support empty input for unique_consecutive (#49978)

paddle/phi/kernels/cpu/unique_consecutive_functor.h

@@ -51,9 +51,11 @@ static void UniqueConsecutiveFlattenedTensor(const Context& context,
     }
   }
 
-  int64_t output_size = p - out_vec.data() + 1;
+  bool is_empty = in.numel() == 0;
+  int64_t output_size = is_empty ? 0 : (p - out_vec.data() + 1);
+
   if (return_counts) {
-    *q = in.numel() - last;
+    if (!is_empty) *q = in.numel() - last;
     counts_vec.resize(output_size);
   }
   out_vec.resize(output_size);

python/paddle/fluid/tests/unittests/test_unique_consecutive_op.py

@@ -32,12 +32,14 @@ def reference_unique_consecutive(X, return_inverse=False, return_counts=False):
         return_counts(bool, optional): If True, also return the counts for each unique consecutive element.
     """
     X = list(X)
+    is_empty = len(X) == 0
     counts_vec = [1] * len(X)
     i = 0
     counts = 1
     last = 0
     inverse_vec = [0] * len(X)
-    inverse_vec[last] = i
+    if not is_empty:
+        inverse_vec[last] = i
     cnt = 0
     while i < len(X) - 1:
         if X[i] == X[i + 1]:
@@ -271,6 +273,40 @@ class TestUniqueConsecutiveCase2API(unittest.TestCase):
                 )
 
 
+class TestUniqueConsecutiveEmptyInput(OpTest):
+    """empty input"""
+
+    def config(self):
+        self.return_inverse = True
+        self.return_counts = True
+        self.python_api = paddle.unique_consecutive
+
+    def init_kernel_type(self):
+        self.dtype = "float32" if core.is_compiled_with_rocm() else "float64"
+
+    def setUp(self):
+        self.init_kernel_type()
+        self.config()
+        self.op_type = "unique_consecutive"
+        x = np.array([]).astype(self.dtype)
+        result = reference_unique_consecutive(
+            x, self.return_inverse, self.return_counts
+        )
+        out = reference_unique_consecutive(x)
+        out = np.array(out).astype(self.dtype)
+        self.inputs = {
+            'X': x,
+        }
+        self.python_out_sig = ["Out"]
+        self.attrs = {'dtype': int(core.VarDesc.VarType.INT32)}
+        self.outputs = {
+            'Out': out,
+        }
+
+    def test_check_output(self):
+        self.check_output(check_eager=True)
+
+
 if __name__ == "__main__":
     paddle.enable_static()
     unittest.main()