arange.infer_shape upcast more and be safe again uint64. The old upcast was ok, as the elemw

theano/tensor/basic.py

@@ -4193,20 +4193,27 @@ class ARange(Op):
                 pass
             return False
 
+        def upcast(var):
+            if ('int' in var.dtype and
+                # We do not want to cast uint64 to int64 as this can
+                # loose information. If we upcast uint64 with int64,
+                # this give float64. This is safer then checking for
+                # uint64 in case we support [u]int128 or other in the
+                # future.
+                scal.upcast(var.dtype, 'int64') == 'int64'):
+                return cast(var, 'int64')
+            return var
+
         if is_constant_value(step, 1):
             if is_constant_value(start, 0):
                 return [(cast(stop, 'int64'),)]
             else:
-                if 'int' in stop.dtype:
-                    stop = cast(stop, 'int64')
-                elif 'int' in start.dtype:
-                    start = cast(start, 'int64')
+                stop = upcast(stop)
+                start = upcast(start)
                 return [(maximum(cast(stop - start, 'int64'), 0),)]
         else:
-            if 'int' in stop.dtype:
-                stop = cast(stop, 'int64')
-            elif 'int' in start.dtype:
-                start = cast(start, 'int64')
+            stop = upcast(stop)
+            start = upcast(start)
             return [(maximum(cast(ceil(cast((stop - start), 'float64')
                                        / step), 'int64'), 0),)]
 

theano/tensor/tests/test_basic.py

@@ -5101,7 +5101,7 @@ class TestARange(unittest.TestCase):
             mode = 'FAST_RUN'
         mode = compile.mode.get_mode(mode).excluding('fusion')
         f = function([start, stop, step], out.shape, mode=mode)
-        assert len(f.maker.fgraph.toposort()) == 8
+        assert len(f.maker.fgraph.toposort()) == 9
 
         if config.cast_policy == 'custom':
             assert out.dtype == start.type.dtype
@@ -5122,7 +5122,7 @@ class TestARange(unittest.TestCase):
 
         out = arange(start, stop, 1)
         f = function([start, stop], out.shape, mode=mode)
-        assert len(f.maker.fgraph.toposort()) == 4
+        assert len(f.maker.fgraph.toposort()) == 5
 #4 [Elemwise{sub,no_inplace}(stop, start), Elemwise{Cast{int64}}(Elemwise{sub,no_inplace}.0), Elemwise{Maximum{output_types_preference=transfer_type{0}}}[(0, 0)](Elemwise{Cast{int64}}.0, 0), MakeVector(Elemwise{Maximum{output_types_preference=transfer_type{0}}}[(0, 0)].0)]
         if config.cast_policy == 'custom':
             assert out.dtype == start.type.dtype