adjust remove rule for variables

paddle/fluid/framework/block_desc.cc

@@ -147,40 +147,51 @@ void BlockDesc::RemoveOp(size_t s, size_t e) {
   if (ops_.begin() + s == ops_.end() || ops_.begin() + e == ops_.end()) {
     return;
   }
+  auto get_vars = [](std::deque<std::unique_ptr<OpDesc>>::iterator &op,
+                     std::vector<std::string> &v) {
+    auto in_names = (*op)->InputArgumentNames();
+    v.insert(v.end(), in_names.begin(), in_names.end());
+    auto out_names = (*op)->OutputArgumentNames();
+    v.insert(v.end(), out_names.begin(), out_names.end());
+    std::sort(v.begin(), v.end());
+    auto last = std::unique(v.begin(), v.end());
+    v.erase(last, v.end());
+  };
   need_update_ = true;
-  std::vector<std::string> vars1;  // input vars from delete ops
-  for (auto it = ops_.begin() + s; it != ops_.begin() + e; it++) {
-    // delete all output vars
-    auto out_names = (*it)->OutputArgumentNames();
-    for (auto n : out_names) {
-      vars_.erase(vars_.find(n));
-    }
-    // collect all input vars from remove ops
-    auto in_names = (*it)->InputArgumentNames();
-    vars1.insert(vars1.end(), in_names.begin(), in_names.end());
-  }
-  ops_.erase(ops_.begin() + s, ops_.begin() + e);
 
-  // collect input and output vars from remain ops
-  std::vector<std::string> vars2;
+  for (size_t i = s; i < e; i++) {
+    // since remove op one by one, every time remove the first op.
+    auto op = ops_.begin() + s;
+
+    // collect input and output variables from current delete op
+    std::vector<std::string> cur_vars;
+    get_vars(op, cur_vars);
+
+    // remove current op
+    ops_.erase(ops_.begin() + s);
+
+    // collect input and output variables from other ops
+    std::vector<std::string> other_vars;
     for (auto it = ops_.begin(); it != ops_.end(); it++) {
-    auto in_names = (*it)->InputArgumentNames();
-    auto out_names = (*it)->OutputArgumentNames();
-    vars2.insert(vars2.end(), in_names.begin(), in_names.end());
-    vars2.insert(vars2.end(), out_names.begin(), out_names.end());
+      get_vars(it, other_vars);
     }
 
-  // delete input vars if no other op use it.
-  std::vector<std::string> del_vars;
-  std::sort(vars1.begin(), vars1.end());
-  std::unique(vars1.begin(), vars1.end());
-  std::sort(vars2.begin(), vars2.end());
-  std::unique(vars2.begin(), vars2.end());
-  // del_vars = vars1 -  vars1 ^ vars2
-  std::set_difference(vars1.begin(), vars1.end(), vars2.begin(), vars2.end(),
-                      std::inserter(del_vars, del_vars.end()));
-  for (auto it = del_vars.begin(); it != del_vars.end(); it++) {
-    vars_.erase(vars_.find(*it));
+    // variables should be deleted
+    std::vector<std::string> delete_vars;
+    // delete_vars = cur_vars -  cur_vars ^ other_input_vars
+    std::set_difference(cur_vars.begin(), cur_vars.end(), other_vars.begin(),
+                        other_vars.end(),
+                        std::inserter(delete_vars, delete_vars.end()));
+    // remove variables
+    for (size_t i = 0; i < delete_vars.size(); i++) {
+      auto name = delete_vars[i];
+      auto it = vars_.find(name);
+      PADDLE_ENFORCE(it != vars_.end(),
+                     "%s is not in variable list, it should not be deleted",
+                     name);
+      vars_.erase(it);
+      VLOG(3) << "deleting variable " << name;
+    }
   }
 }
 

paddle/fluid/framework/block_desc.h

@@ -89,6 +89,11 @@ class BlockDesc {
 
   OpDesc *InsertOp(size_t index);
 
+  /*
+   * Remove Op and its input/output variables.
+   * Note that for either input or ouput variable, if it is also an input or
+   * output variable of other ops, we should remain it.
+   */
   void RemoveOp(size_t s, size_t e);
 
   std::vector<OpDesc *> AllOps() const;

python/paddle/fluid/tests/unittests/test_protobuf_descs.py

@@ -197,13 +197,14 @@ class TestBlockDesc(unittest.TestCase):
         var2 = block.var("var2")
         var3 = block.var("var3")
         var4 = block.var("var4")
+        var5 = block.var("var5")
         op1.set_input("X", ["var1", "var2"])
-        op1.set_output("Y", ["var3"])
+        op1.set_output("Y", ["var3", "var4"])
         op2.set_input("X", ["var1"])
-        op2.set_output("Y", ["var4"])
+        op2.set_output("Y", ["var4", "var5"])
 
         # remove op1, its input var2 and output var3 will be removed at the same time,
-        # but its input var1 will not be removed since var1 is also an input for op2.
+        # but its input var1 and output var4 will not be removed since they are used for op2.
         block.remove_op(0, 1)
 
         all_ops = []
@@ -211,7 +212,7 @@ class TestBlockDesc(unittest.TestCase):
             all_ops.append(block.op(idx))
         self.assertEqual(all_ops, [op2])
         all_vars = block.all_vars()
-        self.assertEqual(set(all_vars), {var1, var4})
+        self.assertEqual(set(all_vars), {var1, var4, var5})
 
 
 if __name__ == '__main__':