Index: clangd/index/Index.h
===================================================================
--- clangd/index/Index.h
+++ clangd/index/Index.h
@@ -17,6 +17,7 @@
 #include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/StringExtras.h"
+#include "llvm/Support/StringSaver.h"
 #include <array>
 #include <string>
 
@@ -257,6 +258,8 @@
   // The frozen SymbolSlab will use less memory.
   class Builder {
   public:
+    Builder() : UniqueStrings(Arena) {}
+
     // Adds a symbol, overwriting any existing one with the same ID.
     // This is a deep copy: underlying strings will be owned by the slab.
     void insert(const Symbol &S);
@@ -273,7 +276,7 @@
   private:
     llvm::BumpPtrAllocator Arena;
     // Intern table for strings. Contents are on the arena.
-    llvm::DenseSet<llvm::StringRef> Strings;
+    llvm::UniqueStringSaver UniqueStrings;
     std::vector<Symbol> Symbols;
     // Values are indices into Symbols vector.
     llvm::DenseMap<SymbolID, size_t> SymbolIndex;
Index: clangd/index/Index.cpp
===================================================================
--- clangd/index/Index.cpp
+++ clangd/index/Index.cpp
@@ -77,16 +77,10 @@
 }
 
 // Copy the underlying data of the symbol into the owned arena.
-static void own(Symbol &S, DenseSet<StringRef> &Strings,
+static void own(Symbol &S, llvm::UniqueStringSaver &Strings,
                 BumpPtrAllocator &Arena) {
   // Intern replaces V with a reference to the same string owned by the arena.
-  auto Intern = [&](StringRef &V) {
-    auto R = Strings.insert(V);
-    if (R.second) { // New entry added to the table, copy the string.
-      *R.first = V.copy(Arena);
-    }
-    V = *R.first;
-  };
+  auto Intern = [&](StringRef &V) { V = Strings.save(V); };
 
   // We need to copy every StringRef field onto the arena.
   Intern(S.Name);
@@ -114,10 +108,10 @@
   auto R = SymbolIndex.try_emplace(S.ID, Symbols.size());
   if (R.second) {
     Symbols.push_back(S);
-    own(Symbols.back(), Strings, Arena);
+    own(Symbols.back(), UniqueStrings, Arena);
   } else {
     auto &Copy = Symbols[R.first->second] = S;
-    own(Copy, Strings, Arena);
+    own(Copy, UniqueStrings, Arena);
   }
 }
 
@@ -128,7 +122,7 @@
             [](const Symbol &L, const Symbol &R) { return L.ID < R.ID; });
   // We may have unused strings from overwritten symbols. Build a new arena.
   BumpPtrAllocator NewArena;
-  DenseSet<StringRef> Strings;
+  llvm::UniqueStringSaver Strings(NewArena);
   for (auto &S : Symbols)
     own(S, Strings, NewArena);
   return SymbolSlab(std::move(NewArena), std::move(Symbols));
Index: docs/clang-tidy/checks/abseil-duration-division.rst
===================================================================
--- /dev/null
+++ docs/clang-tidy/checks/abseil-duration-division.rst
@@ -0,0 +1,36 @@
+.. title:: clang-tidy - abseil-duration-division
+
+abseil-duration-division
+========================
+
+``absl::Duration`` arithmetic works like it does with integers. That means that
+division of two ``absl::Duration`` objects returns an ``int64`` with any fractional
+component truncated toward 0. See `this link <https://github.com/abseil/abseil-cpp/blob/29ff6d4860070bf8fcbd39c8805d0c32d56628a3/absl/time/time.h#L137>`_ for more information on arithmetic with ``absl::Duration``.
+
+For example:
+
+.. code-block:: c++
+
+ absl::Duration d = absl::Seconds(3.5);
+ int64 sec1 = d / absl::Seconds(1);     // Truncates toward 0.
+ int64 sec2 = absl::ToInt64Seconds(d);  // Equivalent to division.
+ assert(sec1 == 3 && sec2 == 3);
+
+ double dsec = d / absl::Seconds(1);  // WRONG: Still truncates toward 0.
+ assert(dsec == 3.0);
+
+If you want floating-point division, you should use either the
+``absl::FDivDuration()`` function, or one of the unit conversion functions such
+as ``absl::ToDoubleSeconds()``. For example:
+
+.. code-block:: c++
+
+ absl::Duration d = absl::Seconds(3.5);
+ double dsec1 = absl::FDivDuration(d, absl::Seconds(1));  // GOOD: No truncation.
+ double dsec2 = absl::ToDoubleSeconds(d);                 // GOOD: No truncation.
+ assert(dsec1 == 3.5 && dsec2 == 3.5);
+
+
+This check looks for uses of ``absl::Duration`` division that is done in a
+floating-point context, and recommends the use of a function that returns a
+floating-point value.