Fix a bug in the VM/CVM GC that was the default in the trunk since the 5 July 2012.

theano/gof/lazylinker_c.c.txt

@@ -771,7 +771,8 @@ int lazy_rec_eval(CLazyLinker * self, Py_ssize_t var_idx, PyObject*one, PyObject
 
           Py_INCREF(Py_None);
           err = PyList_SetItem(self->var_value_cells[i_idx], 0, Py_None);
-          self->var_computed[i_idx] = 0;
+//See the Stack gc implementation for why we change it to 2 and not 0.
+          self->var_computed[i_idx] = 2;
           if (err) goto fail;
         }
     }
@@ -972,7 +973,7 @@ static PyTypeObject lazylinker_ext_CLazyLinkerType = {
 
 static PyObject * get_version(PyObject *dummy, PyObject *args)
 {
-  PyObject *result = PyFloat_FromDouble(0.17);
+  PyObject *result = PyFloat_FromDouble(0.18);
   return result;
 }
 

theano/gof/lazylinker_c.py

@@ -13,7 +13,7 @@ if config.compiledir not in sys.path:
     sys.path.append(config.compiledir)
 
 force_compile = False
-version = 0.17 # must match constant returned in function get_version()
+version = 0.18 # must match constant returned in function get_version()
 
 
 try:

theano/gof/vm.py

@@ -369,7 +369,14 @@ class Stack(VM):
                                 if all(compute_map[v][0]
                                         for v in dependencies[i]):
                                     storage_map[i][0] = None
-                                    compute_map[i][0] = 0
+                                    #DO NOT set compute_map to 0
+
+                                    #If values become False and the
+                                    #current_apply is still in the
+                                    #stack, this will cause it to be
+                                    #recomputed! This can cause wrong value
+                                    #with some combiation of inplace op.
+                                    compute_map[i][0] = 2
                 elif not computed_ins:
                     # -- Non-lazy case, need inputs
                     apply_stack.append(current_apply)
@@ -429,7 +436,9 @@ class Stack(VM):
                                         break
                                 if empty_storage_map:
                                     storage_map[i][0] = None
-                                    compute_map[i][0] = None
+                                    #See the not lazy gc code for explanations
+                                    #Of compute_map change
+                                    compute_map[i][0] = 2
 
         # Hacky coarse gc final pass
         # This is required until we have a proper gc algorithm for graphs with