Fixed infinite canonizer loop with NaN constants

theano/tensor/opt.py

@@ -2761,19 +2761,29 @@ class Canonizer(gof.LocalOptimizer):
         # Wrapping ct in a Constant with the right dtype
         ct = [T.constant(c, dtype=out_type.dtype) for c in ct]
 
-        if orig_num and len(numct) == 1 and len(denumct) == 0 and ct and\
-                N.all([c.data for c in ct] == self.get_constant(orig_num[0])):
-            # this is an important trick :( if it so happens that:
+        if orig_num and len(numct) == 1 and len(denumct) == 0 and ct:
+            # In that case we should only have one constant in `ct`.
+            assert len(ct) == 1
+            first_num_ct = self.get_constant(orig_num[0])
+            if first_num_ct is not None and ct[0].type.values_eq(ct[0].data,
+                                                                 first_num_ct):
+                # This is an important trick :( if it so happens that:
                 # * there's exactly one constant on the numerator and none on
                 #   the denominator
-            # * it's not the neutral element (ct is an empty list in that case)
-            # * the constant is the same as the first argument in the numerator
-            # Then we return very exactly the original num/denum
+                # * it's not the neutral element (ct is an empty list in that
+                #   case)
+                # * the constant is the same as the first argument in the
+                #   numerator (we only check the first argument because the
+                #   canonizer puts the computed constants first)
+                # -> then we return very exactly the original num/denum.
                 # If we don't do that the optimizer will just loop
                 # infinitely because it will not catch on that there are
                 # no changes to be made and everytime it will want to
                 # replace something by the same thing...
+                # Note that it is important to use `values_eq` instead of
+                # the == operator, to handle NaN values correctly.
                 return orig_num, orig_denum
+
         return ct + num, denum
 
     def transform(self, node):