[NFC] Use unique_ptr in SparseSet

This allows implementing the move constructor.

llvm/include/llvm/ADT/SparseSet.h

@@ -129,7 +129,12 @@ class SparseSet {
   using DenseT = SmallVector<ValueT, 8>;
   using size_type = unsigned;
   DenseT Dense;
-  SparseT *Sparse = nullptr;
+
+  struct Deleter {
+    void operator()(SparseT *S) { free(S); }
+  };
+  std::unique_ptr<SparseT, Deleter> Sparse;
+
   unsigned Universe = 0;
   KeyFunctorT KeyIndexOf;
   SparseSetValFunctor<KeyT, ValueT, KeyFunctorT> ValIndexOf;
@@ -144,7 +149,7 @@ class SparseSet {
   SparseSet() = default;
   SparseSet(const SparseSet &) = delete;
   SparseSet &operator=(const SparseSet &) = delete;
-  ~SparseSet() { free(Sparse); }
+  SparseSet(SparseSet &&) = default;
 
   /// setUniverse - Set the universe size which determines the largest key the
   /// set can hold.  The universe must be sized before any elements can be
@@ -159,11 +164,10 @@ class SparseSet {
     // Hysteresis prevents needless reallocations.
     if (U >= Universe/4 && U <= Universe)
       return;
-    free(Sparse);
     // The Sparse array doesn't actually need to be initialized, so malloc
     // would be enough here, but that will cause tools like valgrind to
     // complain about branching on uninitialized data.
-    Sparse = static_cast<SparseT*>(safe_calloc(U, sizeof(SparseT)));
+    Sparse.reset(static_cast<SparseT *>(safe_calloc(U, sizeof(SparseT))));
     Universe = U;
   }
 
@@ -205,7 +209,7 @@ class SparseSet {
     assert(Idx < Universe && "Key out of range");
     assert(Sparse != nullptr && "Invalid sparse type");
     const unsigned Stride = std::numeric_limits<SparseT>::max() + 1u;
-    for (unsigned i = Sparse[Idx], e = size(); i < e; i += Stride) {
+    for (unsigned i = Sparse.get()[Idx], e = size(); i < e; i += Stride) {
       const unsigned FoundIdx = ValIndexOf(Dense[i]);
       assert(FoundIdx < Universe && "Invalid key in set. Did object mutate?");
       if (Idx == FoundIdx)
@@ -255,7 +259,7 @@ class SparseSet {
     iterator I = findIndex(Idx);
     if (I != end())
       return std::make_pair(I, false);
-    Sparse[Idx] = size();
+    Sparse.get()[Idx] = size();
     Dense.push_back(Val);
     return std::make_pair(end() - 1, true);
   }
@@ -292,7 +296,7 @@ class SparseSet {
       *I = Dense.back();
       unsigned BackIdx = ValIndexOf(Dense.back());
       assert(BackIdx < Universe && "Invalid key in set. Did object mutate?");
-      Sparse[BackIdx] = I - begin();
+      Sparse.get()[BackIdx] = I - begin();
     }
     // This depends on SmallVector::pop_back() not invalidating iterators.
     // std::vector::pop_back() doesn't give that guarantee.