Use static local variable instead of global variable for safty (#26018)

* remove global variable

* refine code

paddle/fluid/framework/unused_var_check.cc

@@ -28,16 +28,32 @@ DEFINE_bool(enable_unused_var_check, false,
             "Checking whether operator contains unused inputs, "
             "especially for grad operator. It should be in unittest.");
 
-// NOTE(zhiqiu): Currently, there are some operators which involves unused
-// inputs and cannot be removed from the allow_list below.
-// They can be mainly divided into four categories:
-// 0: the inputs of which are only used in if branch, or used in cuda kernel but
-// not in cpu kernel;
-// 1: the inputs of which are used to indicate dtype of outputs;
-// 2: the inputs of which are used in fused operators.
-// The category number is presented in the comments after each operator.
+namespace paddle {
+namespace framework {
+
+std::unordered_set<std::string> *GetThreadLocalUsedVarNameSet() {
+  thread_local std::unordered_set<std::string> used_var_name_set;
+  return &used_var_name_set;
+}
+
+void LogVarUsageIfUnusedVarCheckEnabled(const std::string &name) {
+  if (FLAGS_enable_unused_var_check) {
+    VLOG(6) << "Variable used:" << name;
+    GetThreadLocalUsedVarNameSet()->insert(name);
+  }
+}
 
-const std::unordered_set<std::string> op_with_unsed_vars_allow_list = {
+static const std::unordered_set<std::string> &GetOpWithUnusedVarAllowSet() {
+  // NOTE(zhiqiu): Currently, there are some operators which involves unused
+  // inputs and cannot be removed from the allow_list below.
+  // They can be mainly divided into four categories:
+  // 0: the inputs of which are only used in if branch, or used in cuda kernel
+  // but not in cpu kernel; 1: the inputs of which are used to indicate dtype of
+  // outputs; 2: the inputs of which are used in fused operators. The category
+  // number is presented in the comments after each operator.
+  // Use pointer here for safe static deinitialization
+  static auto *allow_set = new std::unordered_set<std::string>({
+      // called once
       "batch_norm",                      // 0
       "batch_norm_grad",                 // 0
       "sync_batch_norm",                 // 0
@@ -57,27 +73,14 @@ const std::unordered_set<std::string> op_with_unsed_vars_allow_list = {
       "fused_batch_norm_act",            // 2
       "fused_batch_norm_act_grad",       // 2
       "data_norm",                       // 0
-    "data_norm_grad",                  // 0
-};
-
-namespace paddle {
-namespace framework {
-
-std::unordered_set<std::string> *GetThreadLocalUsedVarNameSet() {
-  thread_local std::unordered_set<std::string> used_var_name_set;
-  return &used_var_name_set;
-}
-
-void LogVarUsageIfUnusedVarCheckEnabled(const std::string &name) {
-  if (FLAGS_enable_unused_var_check) {
-    VLOG(6) << "Variable used:" << name;
-    GetThreadLocalUsedVarNameSet()->insert(name);
-  }
+      "data_norm_grad",                  // 0);
+  });
+  return *allow_set;
 }
 
 void CheckUnusedVar(const OperatorBase &op, const Scope &scope) {
   // skip op in allow list.
-  if (op_with_unsed_vars_allow_list.count(op.Type()) != 0) {
+  if (GetOpWithUnusedVarAllowSet().count(op.Type()) != 0) {
     return;
   }
   auto *used_set = GetThreadLocalUsedVarNameSet();