Fix bug in local_abs_merge optimization

theano/tensor/opt.py

@@ -3659,7 +3659,10 @@ def local_abs_merge(node):
             if i.owner and i.owner.op == T.abs_:
                 inputs.append(i.owner.inputs[0])
             else:
-                const = get_scalar_constant_value(i)
+                try:
+                    const = get_scalar_constant_value(i)
+                except NotScalarConstantError:
+                    return False
                 if not (const >= 0).all():
                     return False
                 inputs.append(i)

theano/tensor/tests/test_opt.py

@@ -782,6 +782,19 @@ def test_local_merge_abs():
     assert len(f.maker.fgraph.toposort()) == 2
 
 
+def test_merge_abs_bugfix():
+    # Test crash in optimization reported by Jeremiah Lowin at
+    # https://groups.google.com/d/topic/theano-users/TaXfqXP2Mj0/discussion
+    input = T.matrix()
+    # normalize on cols
+    step1 = input / input.sum(0)
+    # normalize on rows
+    step2 = step1 / step1.sum(1)
+    # get l1 norm
+    l1_norm = T.abs_(step2).sum()
+    theano.function([input], T.grad(l1_norm, input))
+
+
 def test_mixeddiv():
     """Test that int division is preserved"""
     i = iscalar()