Fix the constant cache during compilation.

theano/gof/opt.py

@@ -76,7 +76,13 @@ class Optimizer(object):
           opt.apply(fgraph)
         """
         self.add_requirements(fgraph)
-        return self.apply(fgraph, *args, **kwargs)
+        try:
+            orig = theano.tensor.basic.constant.enable
+            theano.tensor.basic.constant.enable = False
+            ret = self.apply(fgraph, *args, **kwargs)
+        finally:
+            theano.tensor.basic.constant.enable = orig
+        return ret
 
     def __call__(self, fgraph):
         """WRITEME

theano/tensor/basic.py

@@ -411,6 +411,8 @@ def constant(x, name=None, ndim=None, dtype=None):
     #But we don't want to cache too much stuff
     #So we cache integer with dtype [u]int and float where the value is between -10 and 10
     #We want to cache all broadcast pattern for scalar.
+    if not constant.enable:
+        return ret
     sig = ret.signature()
     if (sig not in constant_cache and ret.data.size == 1 and
         ret.data <= 10 and ret.data >= -10 and
@@ -419,6 +421,7 @@ def constant(x, name=None, ndim=None, dtype=None):
         constant_cache[sig] = ret
 
     return constant_cache.get(sig, ret)
+constant.enable = True
 
 
 def _obj_is_wrappable_as_tensor(x):