diff --git a/clang-tools-extra/clangd/index/dex/Dex.cpp b/clang-tools-extra/clangd/index/dex/Dex.cpp
--- a/clang-tools-extra/clangd/index/dex/Dex.cpp
+++ b/clang-tools-extra/clangd/index/dex/Dex.cpp
@@ -21,6 +21,7 @@
 #include "llvm/Support/ScopedPrinter.h"
 #include <algorithm>
 #include <queue>
+#include <utility>
 
 namespace clang {
 namespace clangd {
@@ -76,23 +77,42 @@
   }
 
   // Assemble the final compressed posting lists for the added symbols.
-  llvm::DenseMap<Token, PostingList> build() {
+  llvm::DenseMap<Token, PostingList> build() && {
     llvm::DenseMap<Token, PostingList> Result(/*InitialReserve=*/
                                               TrigramDocs.size() +
                                               RestrictedCCDocs.size() +
                                               TypeDocs.size() +
                                               ScopeDocs.size() +
                                               ProximityDocs.size());
-    for (const auto &E : TrigramDocs)
-      Result.try_emplace(Token(Token::Kind::Trigram, E.first.str()), E.second);
-    for (const auto &E : TypeDocs)
-      Result.try_emplace(Token(Token::Kind::Type, E.first()), E.second);
-    for (const auto &E : ScopeDocs)
-      Result.try_emplace(Token(Token::Kind::Scope, E.first()), E.second);
-    for (const auto &E : ProximityDocs)
-      Result.try_emplace(Token(Token::Kind::ProximityURI, E.first()), E.second);
-    if (!RestrictedCCDocs.empty())
-      Result.try_emplace(RestrictedForCodeCompletion, RestrictedCCDocs);
+    for (auto &E : TrigramDocs) {
+      E.second.shrink_to_fit();
+      Result.try_emplace(Token(Token::Kind::Trigram, E.first.str()),
+                         std::move(E.second));
+    }
+    TrigramDocs.clear();
+    for (auto &E : TypeDocs) {
+      E.second.shrink_to_fit();
+      Result.try_emplace(Token(Token::Kind::Type, E.first()),
+                         std::move(E.second));
+    }
+    TypeDocs.clear();
+    for (auto &E : ScopeDocs) {
+      E.second.shrink_to_fit();
+      Result.try_emplace(Token(Token::Kind::Scope, E.first()),
+                         std::move(E.second));
+    }
+    ScopeDocs.clear();
+    for (auto &E : ProximityDocs) {
+      E.second.shrink_to_fit();
+      Result.try_emplace(Token(Token::Kind::ProximityURI, E.first()),
+                         std::move(E.second));
+    }
+    ProximityDocs.clear();
+    if (!RestrictedCCDocs.empty()) {
+      RestrictedCCDocs.shrink_to_fit();
+      Result.try_emplace(RestrictedForCodeCompletion,
+                         std::move(RestrictedCCDocs));
+    }
     return Result;
   }
 };
@@ -125,7 +145,7 @@
   IndexBuilder Builder;
   for (DocID SymbolRank = 0; SymbolRank < Symbols.size(); ++SymbolRank)
     Builder.add(*Symbols[SymbolRank], SymbolRank);
-  InvertedIndex = Builder.build();
+  InvertedIndex = std::move(Builder).build();
 }
 
 std::unique_ptr<Iterator> Dex::iterator(const Token &Tok) const {