Provide move semantics for (Small)BitVector.

CodeGen makes a lot of BitVector copies.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157826 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/SmallBitVector.h

@@ -15,6 +15,7 @@
 #define LLVM_ADT_SMALLBITVECTOR_H
 
 #include "llvm/ADT/BitVector.h"
+#include "llvm/Support/Compiler.h"
 #include "llvm/Support/MathExtras.h"
 #include <cassert>
 
@@ -152,6 +153,12 @@ public:
       switchToLarge(new BitVector(*RHS.getPointer()));
   }
 
+#if LLVM_USE_RVALUE_REFERENCES
+  SmallBitVector(SmallBitVector &&RHS) : X(RHS.X) {
+    RHS.X = 1;
+  }
+#endif
+
   ~SmallBitVector() {
     if (!isSmall())
       delete getPointer();
@@ -422,6 +429,16 @@ public:
     return *this;
   }
 
+#if LLVM_USE_RVALUE_REFERENCES
+  const SmallBitVector &operator=(SmallBitVector &&RHS) {
+    if (this != &RHS) {
+      clear();
+      swap(RHS);
+    }
+    return *this;
+  }
+#endif
+
   void swap(SmallBitVector &RHS) {
     std::swap(X, RHS.X);
   }