use std::is_sorted

fix comment
test=develop

paddle/fluid/framework/lod_tensor.cc

@@ -157,17 +157,9 @@ bool CheckLoD(const LoD &in, int tensor_height) {
     if (level.size() < 2) return false;
     // check: the first offset(the begin offset) of each level should be 0.
     if (level.front() != 0) return false;
-    // check: all the offsets in a level should be ascending(no same items
-    // allows).
-    auto beg = level.begin();
-    auto end = level.end();
-    // Do not use std::is_sorted, because we need strictly sorted lod
-    if (beg != end) {
-      for (auto it = beg + 1; it != end; ++it) {
-        if (*(it - 1) >= *it) {
-          return false;
-        }
-      }
+    // check: all the offsets in a level should be ascending(allow same items)
+    if (!std::is_sorted(level.begin(), level.end())) {
+      return false;
     }
   }
   // check: the lowest level's last offset should equals `tensor_height` if

paddle/fluid/framework/lod_tensor_test.cc

@@ -218,9 +218,10 @@ TEST(LoD, CheckLoD) {
   ASSERT_TRUE(CheckLoD(relative_lod, 5));
   ASSERT_FALSE(CheckLoD(relative_lod, 9));
 
-  // check strictly sorted lod
+  // check whether lod is ascending-sorted (allow same items)
   ASSERT_TRUE(CheckLoD({{0, 1, 2, 3, 4, 5}}, 5));
-  ASSERT_FALSE(CheckLoD({{0, 1, 3, 3, 4, 5}}, 5));
+  ASSERT_TRUE(CheckLoD({{0, 1, 3, 3, 4, 5}}, 5));
+  ASSERT_FALSE(CheckLoD({{0, 1, 3, 2, 5}}, 5));
 }
 
 TEST(LoD, CheckAbsLoD) {