Fix gh-5280. Remove isnan from the graph for discrete dtype.

theano/tensor/basic.py

@@ -1825,6 +1825,18 @@ def neq(a, b):
 def isnan(a):
     """isnan(a)"""
 
+# Rename isnan to isnan_ to allow to bypass it when not needed.
+# glibc 2.23 don't allow isnan on int, so we remove it from the graph.
+isnan_ = isnan
+
+
+def isnan(a):
+    """isnan(a)"""
+    if a.dtype in discrete_dtypes:
+        return alloc(numpy.asarray(False, dtype="bool"),
+                     *[a.shape[i] for i in range(a.ndim)])
+    return isnan_(a)
+
 
 @_scal_elemwise
 def isinf(a):

theano/tensor/tests/test_basic.py

@@ -2860,6 +2860,14 @@ def test_nan_inf_constant_signature():
     assert f(numpy.nan) == 0
 
 
+def test_isnan():
+    for x in [tensor.matrix(), tensor.imatrix(), tensor.matrix(dtype='bool')]:
+        y = tensor.isnan(x)
+        assert isinstance(y.owner.op, tensor.Elemwise) == (
+            x.dtype not in tensor.discrete_dtypes)
+        assert y.dtype == 'bool'
+
+
 class T_Shape(unittest.TestCase):
     def test_basic0(self):
         s = shape(numpy.ones((5, 3)))