Added flag, defaulted to False.

theano/compile/function_module.py

@@ -1104,6 +1104,7 @@ class FunctionMaker(object):
                 graph_db = {}
 
             print 'loaded graph_db from %s, size=%d' % (graph_db_file, len(graph_db))
+            if theano.config.cache_optimizations:
                 need_optimize = True
                 # the sole purpose of this loop is to set 'need_optimize'
                 for i, graph_old in enumerate(graph_db.keys()):
@@ -1201,7 +1202,11 @@ class FunctionMaker(object):
                     fgraph = self.fgraph
                 # release stuff
                 release_lock()
-
+            else:
+                start_optimizer = time.time()
+                optimizer_profile = optimizer(fgraph)
+                end_optimizer = time.time()
+                opt_time = end_optimizer - start_optimizer
             print 'opt took %s' % opt_time
             if profile:
                 profile.optimizer_time += opt_time

theano/configdefaults.py

@@ -538,3 +538,10 @@ AddConfigVar('check_input',
               "(particularly for scalars) and reduce the number of generated C "
               "files.",
              BoolParam(True))
+
+AddConfigVar('cache_optimizations',
+             "Specify if the optimization cache should be used. This cache will"
+             "any optimized graph and its optimization. Actually slow downs a lot"
+             "the first optimization, and could possibly still contains some bugs."
+             "Use at your own risks.",
+             BoolParam(False))