[libcxx] Add assertion in deque::pop_back when popping from an empty deque

Also, add tests making sure that vector and deque both catch the problem
when assertions are enabled. Otherwise, deque would segfault and vector
would never terminate.

llvm-svn: 348994

libcxx/include/deque

@@ -987,7 +987,7 @@ public:
 #if _LIBCPP_STD_VER >= 14
         _NOEXCEPT;
 #else
-        _NOEXCEPT_(!__alloc_traits::propagate_on_container_swap::value || 
+        _NOEXCEPT_(!__alloc_traits::propagate_on_container_swap::value ||
                     __is_nothrow_swappable<allocator_type>::value);
 #endif
 protected:
@@ -1156,7 +1156,7 @@ __deque_base<_Tp, _Allocator>::swap(__deque_base& __c)
 #if _LIBCPP_STD_VER >= 14
         _NOEXCEPT
 #else
-        _NOEXCEPT_(!__alloc_traits::propagate_on_container_swap::value || 
+        _NOEXCEPT_(!__alloc_traits::propagate_on_container_swap::value ||
                     __is_nothrow_swappable<allocator_type>::value)
 #endif
 {
@@ -2342,7 +2342,7 @@ deque<_Tp, _Allocator>::__add_front_capacity()
                 _Dp(__a, __base::__block_size));
         __buf.push_back(__hold.get());
         __hold.release();
-    
+
         for (typename __base::__map_pointer __i = __base::__map_.begin();
                 __i != __base::__map_.end(); ++__i)
             __buf.push_back(*__i);
@@ -2604,6 +2604,7 @@ template <class _Tp, class _Allocator>
 void
 deque<_Tp, _Allocator>::pop_back()
 {
+    _LIBCPP_ASSERT(!empty(), "deque::pop_back called for empty deque");
     allocator_type& __a = __base::__alloc();
     size_type __p = __base::size() + __base::__start_ - 1;
     __alloc_traits::destroy(__a, __to_raw_pointer(*(__base::__map_.begin() +
@@ -2854,7 +2855,7 @@ deque<_Tp, _Allocator>::swap(deque& __c)
 #if _LIBCPP_STD_VER >= 14
         _NOEXCEPT
 #else
-        _NOEXCEPT_(!__alloc_traits::propagate_on_container_swap::value || 
+        _NOEXCEPT_(!__alloc_traits::propagate_on_container_swap::value ||
                     __is_nothrow_swappable<allocator_type>::value)
 #endif
 {

libcxx/test/libcxx/containers/sequences/deque/pop_back_empty.pass.cpp

@@ -0,0 +1,25 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <deque>
+
+// pop_back() more than the number of elements in a deque
+
+#define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))
+
+#include <cstdlib>
+#include <deque>
+
+
+int main() {
+    std::deque<int> q;
+    q.push_back(0);
+    q.pop_back();
+    q.pop_back();
+}

libcxx/test/libcxx/containers/sequences/vector/pop_back_empty.pass.cpp

@@ -0,0 +1,25 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <vector>
+
+// pop_back() more than the number of elements in a vector
+
+#define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))
+
+#include <cstdlib>
+#include <vector>
+
+
+int main() {
+    std::vector<int> v;
+    v.push_back(0);
+    v.pop_back();
+    v.pop_back();
+}