SERVER-35851: Check whether the array passed to $in is sorted before calling std::sort

1 files changed, 15 insertions, 7 deletions

diff --git a/src/mongo/db/matcher/expression_leaf.cpp b/src/mongo/db/matcher/expression_leaf.cpp
index 1bbd1389e3e..7226d9111ae 100644
--- a/src/mongo/db/matcher/expression_leaf.cpp
+++ b/src/mongo/db/matcher/expression_leaf.cpp
@@ -477,10 +477,14 @@ void InMatchExpression::_doSetCollator(const CollatorInterface* collator) {
     _collator = collator;
     _eltCmp = BSONElementComparator(BSONElementComparator::FieldNamesMode::kIgnore, _collator);
 
-    // Re-sort the list of equalities according to our current comparator. This is necessary to work
-    // around https://svn.boost.org/trac10/ticket/13140.
-    std::sort(
-        _originalEqualityVector.begin(), _originalEqualityVector.end(), _eltCmp.makeLessThan());
+    if (!std::is_sorted(_originalEqualityVector.begin(),
+                        _originalEqualityVector.end(),
+                        _eltCmp.makeLessThan())) {
+        // Re-sort the list of equalities according to our current comparator. This is necessary to
+        // work around https://svn.boost.org/trac10/ticket/13140.
+        std::sort(
+            _originalEqualityVector.begin(), _originalEqualityVector.end(), _eltCmp.makeLessThan());
+    }
 
     // We need to re-compute '_equalitySet', since our set comparator has changed.
     _equalitySet = _eltCmp.makeBSONEltFlatSet(_originalEqualityVector);
@@ -504,9 +508,13 @@ Status InMatchExpression::setEqualities(std::vector<BSONElement> equalities) {
 
     _originalEqualityVector = std::move(equalities);
 
-    // Sort the list of equalities to work around https://svn.boost.org/trac10/ticket/13140.
-    std::sort(
-        _originalEqualityVector.begin(), _originalEqualityVector.end(), _eltCmp.makeLessThan());
+    if (!std::is_sorted(_originalEqualityVector.begin(),
+                        _originalEqualityVector.end(),
+                        _eltCmp.makeLessThan())) {
+        // Sort the list of equalities to work around https://svn.boost.org/trac10/ticket/13140.
+        std::sort(
+            _originalEqualityVector.begin(), _originalEqualityVector.end(), _eltCmp.makeLessThan());
+    }
 
     _equalitySet = _eltCmp.makeBSONEltFlatSet(_originalEqualityVector);