Add warn_unused_result to empty() on various containers.

empty() doesn't actually empty out the container, making this a common typo.

llvm-svn: 190708

include/llvm/ADT/DenseMap.h

@@ -64,7 +64,9 @@ public:
     return const_iterator(getBucketsEnd(), getBucketsEnd(), true);
   }
 
-  bool empty() const { return getNumEntries() == 0; }
+  bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const {
+    return getNumEntries() == 0;
+  }
   unsigned size() const { return getNumEntries(); }
 
   /// Grow the densemap so that it has at least Size buckets. Does not shrink

include/llvm/ADT/SmallPtrSet.h

@@ -71,7 +71,7 @@ protected:
   ~SmallPtrSetImpl();
 
 public:
-  bool empty() const { return size() == 0; }
+  bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const { return size() == 0; }
   unsigned size() const { return NumElements; }
 
   void clear() {

include/llvm/ADT/SmallVector.h

@@ -53,7 +53,7 @@ public:
     return size_t((char*)CapacityX - (char*)BeginX);
   }
 
-  bool empty() const { return BeginX == EndX; }
+  bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const { return BeginX == EndX; }
 };
 
 template <typename T, unsigned N> struct SmallVectorStorage;

include/llvm/ADT/ilist.h

@@ -382,7 +382,9 @@ public:
 
   // Miscellaneous inspection routines.
   size_type max_size() const { return size_type(-1); }
-  bool empty() const { return Head == 0 || Head == getTail(); }
+  bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const {
+    return Head == 0 || Head == getTail();
+  }
 
   // Front and back accessor functions...
   reference front() {
@@ -534,7 +536,7 @@ public:
   // Functionality derived from other functions defined above...
   //
 
-  size_type size() const {
+  size_type LLVM_ATTRIBUTE_UNUSED_RESULT size() const {
     if (Head == 0) return 0; // Don't require construction of sentinel if empty.
     return std::distance(begin(), end());
   }