Add a SmallBitVector class, which mimics BitVector but uses only

a single pointer (PointerIntPair) member. In "small" mode, the
pointer field is reinterpreted as a set of bits. In "large" mode,
the pointer points to a heap-allocated object.

Also, give BitVector empty and swap functions.

And, add some simple unittests for BitVector and SmallBitVector.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92730 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/BitVector.h

@@ -95,6 +95,9 @@ public:
     delete[] Bits;
   }
 
+  /// empty - Tests whether there are no bits in this bitvector.
+  bool empty() const { return Size == 0; }
+
   /// size - Returns the number of bits in this bitvector.
   unsigned size() const { return Size; }
 
@@ -341,6 +344,12 @@ public:
     return *this;
   }
 
+  void swap(BitVector &RHS) {
+    std::swap(Bits, RHS.Bits);
+    std::swap(Size, RHS.Size);
+    std::swap(Capacity, RHS.Capacity);
+  }
+
 private:
   unsigned NumBitWords(unsigned S) const {
     return (S + BITWORD_SIZE-1) / BITWORD_SIZE;
@@ -406,4 +415,13 @@ inline BitVector operator^(const BitVector &LHS, const BitVector &RHS) {
 }
 
 } // End llvm namespace
+
+namespace std {
+  /// Implement std::swap in terms of BitVector swap.
+  inline void
+  swap(llvm::BitVector &LHS, llvm::BitVector &RHS) {
+    LHS.swap(RHS);
+  }
+}
+
 #endif