marked log softmax optimization as being allowed to remove NaN

theano/tensor/nnet/nnet.py

@@ -1735,7 +1735,11 @@ prepend_1_to_each_row = Prepend_scalar_constant_to_each_row(1.)
 # as  X-X.max(axis=1).dimshuffle(0,'x') - log(exp(X-X.max(axis=1).dimshuffle(0,'x')).sum(axis=1)).dimshuffle(0,'x)
 def make_out_pattern(X):
     stabilized_X = X - X.max(axis=1).dimshuffle(0,'x')
-    return stabilized_X - tensor.log(tensor.exp(stabilized_X).sum(axis=1)).dimshuffle(0,'x')
+    out_var = stabilized_X - tensor.log(tensor.exp(stabilized_X).sum(axis=1)).dimshuffle(0,'x')
+    #tell DEBUG_MODE that it's OK if the original graph produced NaN and the optimized graph does not
+    out_var.values_eq_approx = out_var.type.values_eq_approx_remove_nan
+    return out_var
+
 
 local_log_softmax = gof.PatternSub( in_pattern = (tensor.log, (softmax, 'x')),
                                     out_pattern = (make_out_pattern, 'x'),