Index: clangd/CodeComplete.h
===================================================================
--- clangd/CodeComplete.h
+++ clangd/CodeComplete.h
@@ -145,7 +145,8 @@
   // include is used.
   // If we've bundled together overloads that have different sets of includes,
   // thse includes may not be accurate for all of them.
-  llvm::SmallVector<IncludeCandidate, 1> Includes;
+  using IncludeCandidates = llvm::SmallVector<IncludeCandidate, 1>;
+  IncludeCandidates Includes;
 
   /// Holds information about small corrections that needs to be done. Like
   /// converting '->' to '.' on member access.
Index: clangd/CodeComplete.cpp
===================================================================
--- clangd/CodeComplete.cpp
+++ clangd/CodeComplete.cpp
@@ -320,6 +320,25 @@
   }
 };
 
+// Moves includes that do not need edits (i.e. already exist) to the front.
+CodeCompletion::IncludeCandidates
+moveNonInsertingIncludesToFront(CodeCompletion::IncludeCandidates Includes) {
+  if (Includes.size() <= 1)
+    return Includes;
+  // stable_partition on objects is slow. Do it on pointers instead.
+  llvm::SmallVector<CodeCompletion::IncludeCandidate *, 1> Pointers;
+  for (auto &Inc : Includes)
+    Pointers.push_back(&Inc);
+  std::stable_partition(Pointers.begin(), Pointers.end(),
+                        [](const CodeCompletion::IncludeCandidate *I) {
+                          return !I->Insertion.hasValue();
+                        });
+  CodeCompletion::IncludeCandidates Results;
+  for (auto *Inc : Pointers)
+    Results.push_back(std::move(*Inc));
+  return Results;
+}
+
 // Assembles a code completion out of a bundle of >=1 completion candidates.
 // Many of the expensive strings are only computed at this point, once we know
 // the candidate bundle is going to be returned.
@@ -393,24 +412,21 @@
     };
     bool ShouldInsert = C.headerToInsertIfAllowed().hasValue();
     // Calculate include paths and edits for all possible headers.
+    llvm::SmallVector<CodeCompletion::IncludeCandidate, 1> IncludeCandidates;
     for (const auto &Inc : C.RankedIncludeHeaders) {
       if (auto ToInclude = Inserted(Inc)) {
         CodeCompletion::IncludeCandidate Include;
         Include.Header = ToInclude->first;
         if (ToInclude->second && ShouldInsert)
           Include.Insertion = Includes.insert(ToInclude->first);
-        Completion.Includes.push_back(std::move(Include));
+        IncludeCandidates.push_back(std::move(Include));
       } else
         log("Failed to generate include insertion edits for adding header "
             "(FileURI='{0}', IncludeHeader='{1}') into {2}",
             C.IndexResult->CanonicalDeclaration.FileURI, Inc, FileName);
     }
-    // Prefer includes that do not need edits (i.e. already exist).
-    std::stable_partition(Completion.Includes.begin(),
-                          Completion.Includes.end(),
-                          [](const CodeCompletion::IncludeCandidate &I) {
-                            return !I.Insertion.hasValue();
-                          });
+    Completion.Includes =
+        moveNonInsertingIncludesToFront(std::move(IncludeCandidates));
   }
 
   void add(const CompletionCandidate &C, CodeCompletionString *SemaCCS) {