fix mem opt

Author: dzhwinter

python/paddle/fluid/transpiler/memory_optimization_transpiler.py

@@ -171,7 +171,7 @@ def _dataflow_analyze(self):
                 self._live_out[i] |= self._live_in[s]
             self._live_in[i] = self._uses[i] | (
                 self._live_out[i] - self._defs[i])
-            if live_in[i] != self._live_in[i]:
+            if live_in[i] != set(self._live_in[i]):
                 for d in self._presuccessors[i]:
                     worklist.append(d)