Add flag enabling testing of preallocated storage in DebugMode

theano/compile/debugmode.py

@@ -46,6 +46,10 @@ AddConfigVar('DebugMode.warn_input_not_reused',
          ),
         BoolParam(True))
 
+AddConfigVar('DebugMode.check_preallocated_output',
+        'Test thunks with pre-allocated memory as output storage.',
+        BoolParam(False))
+
 import logging
 _logger=logging.getLogger("theano.compile.debugmode")
 _logger.setLevel(logging.WARNING)
@@ -1194,6 +1198,7 @@ class _Linker(gof.link.LocalLinker):
                             r_vals[r] = storage_map[r][0]
                             storage_map[r][0] = None #clear the storage_map of outputs for the thunk_c
 
+                        if config.DebugMode.check_preallocated_output:
                             ## Then, try to use different output storages
                             # reuse_output: use a copy of the same storage returned the first time
                             # TODO: optimization warning if the storage in reuse_outputs
@@ -1326,7 +1331,7 @@ class _Linker(gof.link.LocalLinker):
                                 r_vals[r] = storage_map[r][0]
                             storage_map[r][0] = None #clear the storage_map for the thunk_c
 
-
+                        if config.DebugMode.check_preallocated_output:
                             ## Then, try to use different output storages
                             # TODO: factorize that code with the one for Python above
                             reuse_outputs = {}