[gcc r14-2797] libstdc++: Avoid bogus overflow warnings in std::vector<bool> [PR110807]

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:7931a1de9ec87b996d51d3d60786f5c81f63919f

commit r14-2797-g7931a1de9ec87b996d51d3d60786f5c81f63919f
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Jul 26 14:09:24 2023 +0100

    libstdc++: Avoid bogus overflow warnings in std::vector<bool> [PR110807]
    
    GCC thinks the allocation can alter the object being copied if it's
    globally reachable, so doesn't realize that [x.begin(), x.end()) after
    the allocation is the same as x.size() before it.
    
    This causes a testsuite failure when testing with -D_GLIBCXX_DEBUG:
    FAIL: 23_containers/vector/bool/swap.cc (test for excess errors)
    A fix is to move the calls to x.begin() and x.end() to before the
    allocation.
    
    A similar problem exists in vector<bool>::_M_insert_range where *this is
    globally reachable, as reported in PR libstdc++/110807. That can also be
    fixed by moving calls to begin() and end() before the allocation.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/110807
            * include/bits/stl_bvector.h (vector(const vector&)): Access
            iterators before allocating.
            * include/bits/vector.tcc (vector<bool>::_M_insert_range):
            Likewise.
            * testsuite/23_containers/vector/bool/110807.cc: New test.

Diff:
---
 libstdc++-v3/include/bits/stl_bvector.h                    |  3 ++-
 libstdc++-v3/include/bits/vector.tcc                       |  5 +++--
 libstdc++-v3/testsuite/23_containers/vector/bool/110807.cc | 14 ++++++++++++++
 3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/libstdc++-v3/include/bits/stl_bvector.h b/libstdc++-v3/include/bits/stl_bvector.h
index ad462c5933c..8d18bcaffd4 100644
--- a/libstdc++-v3/include/bits/stl_bvector.h
+++ b/libstdc++-v3/include/bits/stl_bvector.h
@@ -773,8 +773,9 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       vector(const vector& __x)
       : _Base(_Bit_alloc_traits::_S_select_on_copy(__x._M_get_Bit_allocator()))
       {
+	const_iterator __xbegin = __x.begin(), __xend = __x.end();
 	_M_initialize(__x.size());
-	_M_copy_aligned(__x.begin(), __x.end(), begin());
+	_M_copy_aligned(__xbegin, __xend, begin());
       }
 
 #if __cplusplus >= 201103L
diff --git a/libstdc++-v3/include/bits/vector.tcc b/libstdc++-v3/include/bits/vector.tcc
index f592c72dec2..ada396c9b30 100644
--- a/libstdc++-v3/include/bits/vector.tcc
+++ b/libstdc++-v3/include/bits/vector.tcc
@@ -980,11 +980,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	      {
 		const size_type __len =
 		  _M_check_len(__n, "vector<bool>::_M_insert_range");
+		const iterator __begin = begin(), __end = end();
 		_Bit_pointer __q = this->_M_allocate(__len);
 		iterator __start(std::__addressof(*__q), 0);
-		iterator __i = _M_copy_aligned(begin(), __position, __start);
+		iterator __i = _M_copy_aligned(__begin, __position, __start);
 		__i = std::copy(__first, __last, __i);
-		iterator __finish = std::copy(__position, end(), __i);
+		iterator __finish = std::copy(__position, __end, __i);
 		this->_M_deallocate();
 		this->_M_impl._M_end_of_storage = __q + _S_nword(__len);
 		this->_M_impl._M_start = __start;
diff --git a/libstdc++-v3/testsuite/23_containers/vector/bool/110807.cc b/libstdc++-v3/testsuite/23_containers/vector/bool/110807.cc
new file mode 100644
index 00000000000..5c019bd9524
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/vector/bool/110807.cc
@@ -0,0 +1,14 @@
+// { dg-options "-O2" }
+// { dg-do compile }
+
+// Bug 110807
+// Copy list initialisation of a vector<bool> raises a warning with -O2
+
+#include <vector>
+
+std::vector<bool> byCallSpread;
+
+void f()
+{
+  byCallSpread = {true};
+}