libstdc++: Fix -Warray-bounds warning in std::vector<bool> [PR110498]

In this case, we need to tell the compiler that the current size is not
larger than the new size so that all the existing elements can be copied
to the new storage. This avoids bogus warnings about overflowing the new
storage when the compiler can't tell that that cannot happen.

We might as well also hoist the loads of begin() and end() before the
allocation too. All callers will have loaded at least begin() before
calling _M_reallocate.

libstdc++-v3/ChangeLog:

	PR libstdc++/110498
	* include/bits/vector.tcc (vector<bool, A>::_M_reallocate):
	Hoist loads of begin() and end() before allocation and use them
	to state an unreachable condition.
	* testsuite/23_containers/vector/bool/capacity/110498.cc: New
	test.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
(cherry picked from commit aa3aaf2bfb8fcc17076993df4297597b68bc5f60)

diff --git a/libstdc++-v3/include/bits/vector.tcc b/libstdc++-v3/include/bits/vector.tcc
index dafc2a31a8b4e8190e8b4b5734facbf55a02997d..c59c15beacd939d82cc33ac8a2bd9694cb2a2f15 100644 (file)
--- a/libstdc++-v3/include/bits/vector.tcc
+++ b/libstdc++-v3/include/bits/vector.tcc
@@ -1059,9 +1059,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
     vector<bool, _Alloc>::
     _M_reallocate(size_type __n)
     {
+      const iterator __begin = begin(), __end = end();
+      if (size_type(__end - __begin) > __n)
+       __builtin_unreachable();
       _Bit_pointer __q = this->_M_allocate(__n);
       iterator __start(std::__addressof(*__q), 0);
-      iterator __finish(_M_copy_aligned(begin(), end(), __start));
+      iterator __finish(_M_copy_aligned(__begin, __end, __start));
       this->_M_deallocate();
       this->_M_impl._M_start = __start;
       this->_M_impl._M_finish = __finish;

diff --git a/libstdc++-v3/testsuite/23_containers/vector/bool/capacity/110498.cc b/libstdc++-v3/testsuite/23_containers/vector/bool/capacity/110498.cc
new file mode 100644 (file)
index 0000000..d2d09e1
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/vector/bool/capacity/110498.cc
@@ -0,0 +1,18 @@
+// { dg-options "-O3 -Werror=array-bounds" }
+// { dg-do compile }
+
+// Bug libstdc++/110498
+// Spurious warnings stringop-overflow and array-bounds copying data as bytes
+// into vector::reserve
+
+#include <vector>
+
+void f(std::vector<bool>& v)
+{
+  // Warning emitted when set to any number in the range [1,64].
+  const std::size_t reserve_size = 30;
+
+  v.reserve(reserve_size);
+  v.push_back(0);
+}
+