add use_program_cache to executor.run

Author: jacquesqiao

python/paddle/fluid/executor.py

@@ -226,7 +226,19 @@ def run(self,
             feed_var_name='feed',
             fetch_var_name='fetch',
             scope=None,
-            return_numpy=True):
+            return_numpy=True,
+            use_program_cache=False):
+        """
+        :param program: the program that need to run
+        :param feed: feed variable list
+        :param fetch_list: fetch variable list
+        :param feed_var_name: feed_var_name default to 'feed'
+        :param fetch_var_name: fetch_var_name default to 'fetch'
+        :param scope: the scope used to run this program, you can switch it to different scope.
+        :param return_numpy: convert the fetched tensor to numpy
+        :param use_program_cache: set use_program_cache to true if program not changed compare to the last step.
+        :return:
+        """
         if feed is None:
             feed = {}
         if fetch_list is None:
@@ -244,7 +256,7 @@ def run(self,
         program_cache_key = str(feed.keys() + fetch_list)
         program_cache = self.program_caches.get(program_cache_key, None)
 
-        if program_cache is None:
+        if program_cache is None or not use_program_cache:
             program_cache = program.clone()
             self.program_caches[program_cache_key] = program_cache
 
@@ -266,6 +278,7 @@ def run(self,
                     type=core.VarDesc.VarType.FETCH_LIST,
                     persistable=True)
 
+            # prepend feed operators
             if not has_feed_operators(global_block, feed, feed_var_name):
                 for i, name in enumerate(feed):
                     out = global_block.var(name)
@@ -275,6 +288,7 @@ def run(self,
                         outputs={'Out': [out]},
                         attrs={'col': i})
 
+            # append fetch_operators
             if not has_fetch_operators(global_block, fetch_list,
                                        fetch_var_name):
                 for i, var in enumerate(fetch_list):