Standardize {pred,succ,use,user}_empty()

The functions {pred,succ,use,user}_{begin,end} exist, but many users
have to check *_begin() with *_end() by hand to determine if the
BasicBlock or User is empty. Fix this with a standard *_empty(),
demonstrating a few usecases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225760 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/CFG.h

@@ -93,6 +93,9 @@ inline pred_iterator pred_end(BasicBlock *BB) { return pred_iterator(BB, true);}
 inline const_pred_iterator pred_end(const BasicBlock *BB) {
   return const_pred_iterator(BB, true);
 }
+inline bool pred_empty(const BasicBlock *BB) {
+  return pred_begin(BB) == pred_end(BB);
+}
 
 
 
@@ -257,6 +260,9 @@ inline succ_iterator succ_end(BasicBlock *BB) {
 inline succ_const_iterator succ_end(const BasicBlock *BB) {
   return succ_const_iterator(BB->getTerminator(), true);
 }
+inline bool succ_empty(const BasicBlock *BB) {
+  return succ_begin(BB) == succ_end(BB);
+}
 
 template <typename T, typename U> struct isPodLike<SuccIterator<T, U> > {
   static const bool value = isPodLike<T>::value;

include/llvm/IR/Value.h

@@ -286,6 +286,8 @@ public:
     return iterator_range<const_use_iterator>(use_begin(), use_end());
   }
 
+  bool               user_empty() const { return UseList == nullptr; }
+
   typedef user_iterator_impl<User>       user_iterator;
   typedef user_iterator_impl<const User> const_user_iterator;
   user_iterator       user_begin()       { return user_iterator(UseList); }