From aa3aaf2bfb8fcc17076993df4297597b68bc5f60 Mon Sep 17 00:00:00 2001 From: Jonathan Wakely Date: Fri, 28 Mar 2025 15:41:41 +0000 Subject: [PATCH] libstdc++: Fix -Warray-bounds warning in std::vector [PR110498] MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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::_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 --- libstdc++-v3/include/bits/vector.tcc | 5 ++++- .../vector/bool/capacity/110498.cc | 18 ++++++++++++++++++ 2 files changed, 22 insertions(+), 1 deletion(-) create mode 100644 libstdc++-v3/testsuite/23_containers/vector/bool/capacity/110498.cc diff --git a/libstdc++-v3/include/bits/vector.tcc b/libstdc++-v3/include/bits/vector.tcc index 29aa63e4742..7a92f34ec64 100644 --- a/libstdc++-v3/include/bits/vector.tcc +++ b/libstdc++-v3/include/bits/vector.tcc @@ -1106,9 +1106,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER vector:: _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 index 00000000000..f848edcb25e --- /dev/null +++ b/libstdc++-v3/testsuite/23_containers/vector/bool/capacity/110498.cc @@ -0,0 +1,18 @@ +// { dg-options "-O3 -Werror=array-bounds -fno-assume-sane-operators-new-delete" } +// { dg-do compile } + +// Bug libstdc++/110498 +// Spurious warnings stringop-overflow and array-bounds copying data as bytes +// into vector::reserve + +#include + +void f(std::vector& 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); +} +