Make Canonizer always collapse nested ops (#4)

theano/tensor/opt.py

@@ -4992,8 +4992,18 @@ class Canonizer(gof.LocalOptimizer):
             return len(x) == len(y) and all(np.all(xe == ye) for xe, ye in
                                             zip(x, y))
 
-        if same(orig_num, num) and same(orig_denum, denum):
-            # We return False if there are no changes
+        if (same(orig_num, num) and same(orig_denum, denum) and
+            # Check to see if we've collapsed some nested ops.
+            not (len(orig_denum) == 0 and
+                 # Make sure this change would increase the number of vector
+                 # arguments--decreasing the number of unnecessary `self.main`
+                 # nodes.
+                 len(node.inputs) < len(orig_num)) and
+            # Do a similar check for the reciprocal op.
+            not (self.use_reciprocal and
+                 node.op == self.reciprocal and
+                 len(orig_num) == 0 and node.inputs[0].owner and
+                 len(node.inputs[0].owner.inputs) < len(orig_denum))):
             return False
 
         new = self.merge_num_denum(num, denum)

theano/tensor/tests/test_opt.py

@@ -367,9 +367,9 @@ class test_canonize(unittest.TestCase):
         cases = [
             (fx + fy, (fx, fy), (fxv, fyv), 1, 'float32'),
             (fx * fy, (fx, fy), (fxv, fyv), 1, 'float32'),
-            # (fx+fy+fz,(fx,fy,fz),(fxv,fyv,fzv),1,'float32'),
+            (fx + fy + fz, (fx, fy, fz), (fxv, fyv, fzv), 1, 'float32'),
             # (dx+dy+dz,(dx,dy,dz),(dxv,dyv,dzv),1,'float64'),
-            # (fx*fy*fz,(fx,fy,fz),(fxv,fyv,fzv),1,'float32'),
+            (fx * fy * fz, (fx, fy, fz), (fxv, fyv, fzv), 1, 'float32'),
             # (dx*dy*dz,(dx,dy,dz),(dxv,dyv,dzv),1,'float64'),
             # (fx*fy*(fx+fy+fz),(fx,fy,fz),(fxv,fyv,fzv),2,'float32'),
             # (dx*dy*(dx+dy+dz),(dx,dy,dz),(dxv,dyv,dzv),2,'float64'),
@@ -4988,7 +4988,7 @@ class T_local_erfc(unittest.TestCase):
 
         f = theano.function([x], T.grad(T.log(T.erfc(x)).sum(), x), mode=mode)
 
-        assert len(f.maker.fgraph.apply_nodes) == 23, len(f.maker.fgraph.apply_nodes)
+        assert len(f.maker.fgraph.apply_nodes) == 22, len(f.maker.fgraph.apply_nodes)
         assert all(np.isfinite(f(val)))
         assert f.maker.fgraph.outputs[0].dtype == theano.config.floatX