2 files changed, 34 insertions, 4 deletions

diff --git a/llvm/include/llvm/ADT/FoldingSet.h b/llvm/include/llvm/ADT/FoldingSet.h
index 42e2e612d56..c9205396591 100644
--- a/llvm/include/llvm/ADT/FoldingSet.h
+++ b/llvm/include/llvm/ADT/FoldingSet.h
@@ -122,9 +122,10 @@ protected:
   /// is greater than twice the number of buckets.
   unsigned NumNodes;
 
-  ~FoldingSetImpl();
-
   explicit FoldingSetImpl(unsigned Log2InitSize = 6);
+  FoldingSetImpl(FoldingSetImpl &&Arg);
+  FoldingSetImpl &operator=(FoldingSetImpl &&RHS);
+  ~FoldingSetImpl();
 
 public:
   //===--------------------------------------------------------------------===//
@@ -391,6 +392,10 @@ DefaultContextualFoldingSetTrait<T, Ctx>::ComputeHash(T &X,
 /// implementation of the folding set to the node class T.  T must be a
 /// subclass of FoldingSetNode and implement a Profile function.
 ///
+/// Note that this set type is movable and move-assignable. However, its
+/// moved-from state is not a valid state for anything other than
+/// move-assigning and destroying. This is primarily to enable movable APIs
+/// that incorporate these objects.
 template <class T> class FoldingSet final : public FoldingSetImpl {
 private:
   /// GetNodeProfile - Each instantiatation of the FoldingSet needs to provide a
@@ -415,8 +420,13 @@ private:
 
 public:
   explicit FoldingSet(unsigned Log2InitSize = 6)
-  : FoldingSetImpl(Log2InitSize)
-  {}
+      : FoldingSetImpl(Log2InitSize) {}
+
+  FoldingSet(FoldingSet &&Arg) : FoldingSetImpl(std::move(Arg)) {}
+  FoldingSet &operator=(FoldingSet &&RHS) {
+    (void)FoldingSetImpl::operator=(std::move(RHS));
+    return *this;
+  }
 
   typedef FoldingSetIterator<T> iterator;
   iterator begin() { return iterator(Buckets); }
diff --git a/llvm/lib/Support/FoldingSet.cpp b/llvm/lib/Support/FoldingSet.cpp
index b8538ffe1f9..bb0ec2defef 100644
--- a/llvm/lib/Support/FoldingSet.cpp
+++ b/llvm/lib/Support/FoldingSet.cpp
@@ -232,9 +232,29 @@ FoldingSetImpl::FoldingSetImpl(unsigned Log2InitSize) {
   Buckets = AllocateBuckets(NumBuckets);
   NumNodes = 0;
 }
+
+FoldingSetImpl::FoldingSetImpl(FoldingSetImpl &&Arg)
+    : Buckets(Arg.Buckets), NumBuckets(Arg.NumBuckets), NumNodes(Arg.NumNodes) {
+  Arg.Buckets = nullptr;
+  Arg.NumBuckets = 0;
+  Arg.NumNodes = 0;
+}
+
+FoldingSetImpl &FoldingSetImpl::operator=(FoldingSetImpl &&RHS) {
+  free(Buckets); // This may be null if the set is in a moved-from state.
+  Buckets = RHS.Buckets;
+  NumBuckets = RHS.NumBuckets;
+  NumNodes = RHS.NumNodes;
+  RHS.Buckets = nullptr;
+  RHS.NumBuckets = 0;
+  RHS.NumNodes = 0;
+  return *this;
+}
+
 FoldingSetImpl::~FoldingSetImpl() {
   free(Buckets);
 }
+
 void FoldingSetImpl::clear() {
   // Set all but the last bucket to null pointers.
   memset(Buckets, 0, NumBuckets*sizeof(void*));