Unfuse AllocEmpty with CGemv when useful

theano/tensor/blas_c.py

@@ -799,7 +799,14 @@ def use_c_gemv(node):
 @local_optimizer([CGemv(inplace=False)])
 def make_c_gemv_destructive(node):
     if isinstance(node.op, CGemv) and not node.op.inplace:
-        return [cgemv_inplace(*node.inputs)]
+        inputs = list(node.inputs)
+        dest = inputs[0]
+        if (dest.owner and
+                isinstance(dest.owner.op, T.AllocEmpty) and
+                len(dest.clients) > 1):
+            inputs[0] = T.AllocEmpty(dest.dtype)(*dest.owner.inputs)
+
+        return [cgemv_inplace(*inputs)]
 
 
 # ##### ####### #######

theano/tensor/tests/test_blas_c.py

@@ -256,6 +256,21 @@ class TestCGemv(TestCase, TestOptimizationMixin):
         self.assertRaises(ValueError, f, A_val, ones_3, ones_6)
         self.assertRaises(ValueError, f, A_val, ones_4, ones_6)
 
+    def test_multiple_inplace(self):
+        x = tensor.dmatrix('x')
+        y = tensor.dvector('y')
+        z = tensor.dvector('z')
+        f = theano.function([x, y, z],
+                            [tensor.dot(y, x), tensor.dot(z,x)])
+        vx = numpy.random.rand(3, 3)
+        vy = numpy.random.rand(3)
+        vz = numpy.random.rand(3)
+        out = f(vx, vy, vz)
+        assert numpy.allclose(out[0], numpy.dot(vy, vx))
+        assert numpy.allclose(out[1], numpy.dot(vz, vx))
+        assert len([n for n in f.maker.fgraph.apply_nodes
+                    if isinstance(n.op, tensor.AllocEmpty)]) == 2
+
 
 class TestCGemvFloat32(TestCase, BaseGemv, TestOptimizationMixin):
     mode = mode_blas_opt