add basic logic.

theano/gof/vm.py

@@ -892,18 +892,60 @@ class VM_Linker(link.LocalLinker):
         thunks = []
 
         if self.allow_gc:
+
+            viewed_by = {}
+            for var in fgraph.variables:
+                viewed_by[var] = []
+            view_of = {}
+            dependencies = fgraph.profile.dependencies
+
             for idx in range(len(order)):
                 node = order[idx]
+                dmap = getattr(node.op, 'destroy_map', None)
+                vmap = getattr(node.op, 'view_map', None)
+                reallocated_ins = set([])
+
+                idx_o = 0
+                for out in node.output:
+                    if dmap and idx_o in dmap:
+                        idx_v = dmap[idx_o]
+                        assert len(idx_v) == 1, "Here we only support the possibility to destroy one input"
+                        ins = node.inputs[idx_v[0]]
+                    if vmap and idx_o in vmap:
+                        assert ins is None
+                        idx_v = vmap[idx_o]
+                        assert len(idx_v) == 1, "Here we only support the possibility to view one input"
+                        ins = node.inputs[idx_v[0]]
+                    if ins:
+                        assert isinstance(ins, theano.Variable)
+                        origin = view_of.get(ins, ins)
+                        view_of[out] = origin
+                        viewed_by[origin].append(out)
+                idx_o += 1                        
+
                 for ins in node.inputs:
-                    if ins.ndim == 0 and storage_map[ins][0]:
-                        # check if input variable ndim = 0
+                    assert not (ins in view_of and viewed_by[ins])
+                    if (ins.ndim == 0 and storage_map[ins][0] and ins not in fgraph.outputs and ins.owner and dependencies[ins]):
+                        reuse_outs = []
+                        if ins not in view_of and not viewed_by.get(ins, []):
+                            # where gc
                             for i in range(idx + 1, len(order)):
                                 for outs in order[i].outputs:
                                     if outs.ndim == 0:
-                                    storage_map[outs] = storage_map[ins]
-                                    break
-                            else:continue
-                            break
+                                        reuse_list.append(outs)
+                                        reallocated_ins.add(ins)
+                        elif ins in view_of:
+                            origin = view_of[ins]
+                            viewed_by[origin].remove(ins)
+                            if (not viewed_by[origin] and
+                                    origin not in fgraph.inputs and
+                                    not isinstance(origin, theano.Constant)):
+                                #where gc
+                                for i in range(idx + 1, len(order)):
+                                    for outs in order[i].outputs:
+                                        if outs.ndim == 0:
+                                            reuse_list.append(outs)
+                                            reallocated_ins.add(ins)
 
         for node in order:
             try: