Make get_scalar_constant_value investigate Second as Alloc (so elemwise=False…

theano/tensor/basic.py

@@ -590,6 +590,8 @@ def get_scalar_constant_value(orig_v, elemwise=True,
     ----------
     elemwise : bool
         If False, we won't try to go into elemwise. So this call is faster.
+        But we still investigate in Second Elemwise (as this is a substitute
+        for Alloc)
     only_process_constants : bool
         If True, we only attempt to obtain the value of `orig_v` if it's
         directly constant and don't try to dig through dimshuffles, fills,
@@ -650,13 +652,16 @@ def get_scalar_constant_value(orig_v, elemwise=True,
                     ret = [[None]]
                     v.owner.op.perform(v.owner, const, ret)
                     return ret[0][0].copy()
-            elif elemwise and isinstance(v.owner.op, Elemwise):
+            # In fast_compile, we don't enable local_fill_to_alloc, so
+            # we need to investigate Second as Alloc. So elemwise
+            # don't disable the check for Second.
+            elif isinstance(v.owner.op, Elemwise):
                 if isinstance(v.owner.op.scalar_op, scal.Second):
                     # We don't need both input to be constant for second
                     shp, val = v.owner.inputs
                     v = val
                     continue
-                elif isinstance(v.owner.op.scalar_op,
+                elif elemwise and isinstance(v.owner.op.scalar_op,
                                 get_scalar_constant_value_elemwises):
                     const = [get_scalar_constant_value(i)
                              for i in v.owner.inputs]