[llvm] r245192 - [ADT] Teach FoldingSet to be movable.

[David Blaikie via llvm-commits]

On Sun, Aug 16, 2015 at 4:17 PM, Chandler Carruth via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: chandlerc
> Date: Sun Aug 16 18:17:27 2015
> New Revision: 245192
>
> URL: http://llvm.org/viewvc/llvm-project?rev=245192&view=rev
> Log:
> [ADT] Teach FoldingSet to be movable.
>
> This is a very minimal move support - it leaves the moved-from object in
> a zombie state that is only valid for destruction and move assignment.
> This seems fine to me, and leaving it in the default constructed state
> would require adding more state to the object and potentially allocating
> memory (!!!) and so seems like a Bad Idea.
>

Might be worth a unit test (possibly with a move-only value, or even a
move-and-copyable value that checks that it only gets moved - actually, I
assume neither happens, so perhaps it can be done with a non-copyable,
non-movable type?)

- Dave


>
> Modified:
>     llvm/trunk/include/llvm/ADT/FoldingSet.h
>     llvm/trunk/lib/Support/FoldingSet.cpp
>
> Modified: llvm/trunk/include/llvm/ADT/FoldingSet.h
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/FoldingSet.h?rev=245192&r1=245191&r2=245192&view=diff
>
> ==============================================================================
> --- llvm/trunk/include/llvm/ADT/FoldingSet.h (original)
> +++ llvm/trunk/include/llvm/ADT/FoldingSet.h Sun Aug 16 18:17:27 2015
> @@ -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>
>  /// 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); }
>
> Modified: llvm/trunk/lib/Support/FoldingSet.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/FoldingSet.cpp?rev=245192&r1=245191&r2=245192&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Support/FoldingSet.cpp (original)
> +++ llvm/trunk/lib/Support/FoldingSet.cpp Sun Aug 16 18:17:27 2015
> @@ -232,9 +232,29 @@ FoldingSetImpl::FoldingSetImpl(unsigned
>    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*));
>
>
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