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From: Jonathan Wakely <redi@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r14-9000] libstdc++: Avoid aliasing violation in std::valarray [PR99117] Date: Thu, 15 Feb 2024 11:44:17 +0000 (GMT) [thread overview] Message-ID: <20240215114417.BA595384DEE5@sourceware.org> (raw) https://gcc.gnu.org/g:b58f0e5216a3053486e7f1aa96c3f2443b14d630 commit r14-9000-gb58f0e5216a3053486e7f1aa96c3f2443b14d630 Author: Jonathan Wakely <jwakely@redhat.com> Date: Thu Feb 8 13:59:42 2024 +0000 libstdc++: Avoid aliasing violation in std::valarray [PR99117] The call to __valarray_copy constructs an _Array object to refer to this->_M_data but that means that accesses to this->_M_data are through a restrict-qualified pointer. This leads to undefined behaviour when copying from an _Expr object that actually aliases this->_M_data. Replace the call to __valarray_copy with a plain loop. I think this removes the only use of that overload of __valarray_copy, so it could probably be removed. I haven't done that here. libstdc++-v3/ChangeLog: PR libstdc++/99117 * include/std/valarray (valarray::operator=(const _Expr&)): Use loop to copy instead of __valarray_copy with _Array. * testsuite/26_numerics/valarray/99117.cc: New test. Diff: --- libstdc++-v3/include/std/valarray | 8 +++++++- libstdc++-v3/testsuite/26_numerics/valarray/99117.cc | 17 +++++++++++++++++ 2 files changed, 24 insertions(+), 1 deletion(-) diff --git a/libstdc++-v3/include/std/valarray b/libstdc++-v3/include/std/valarray index a4eecd833f71..46cd57e79821 100644 --- a/libstdc++-v3/include/std/valarray +++ b/libstdc++-v3/include/std/valarray @@ -840,7 +840,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION // _GLIBCXX_RESOLVE_LIB_DEFECTS // 630. arrays of valarray. if (_M_size == __e.size()) - std::__valarray_copy(__e, _M_size, _Array<_Tp>(_M_data)); + { + // Copy manually instead of using __valarray_copy, because __e might + // alias _M_data and the _Array param type of __valarray_copy uses + // restrict which doesn't allow aliasing. + for (size_t __i = 0; __i < _M_size; ++__i) + _M_data[__i] = __e[__i]; + } else { if (_M_data) diff --git a/libstdc++-v3/testsuite/26_numerics/valarray/99117.cc b/libstdc++-v3/testsuite/26_numerics/valarray/99117.cc new file mode 100644 index 000000000000..81621bd079a1 --- /dev/null +++ b/libstdc++-v3/testsuite/26_numerics/valarray/99117.cc @@ -0,0 +1,17 @@ +// { dg-do run { target c++11 } } + +// PR libstdc++/99117 cannot accumulate std::valarray + +#include <valarray> +#include <vector> +#include <testsuite_hooks.h> + +int main() +{ + std::vector<std::valarray<int>> v = {{1,1}, {2,2}}; + std::valarray<int> sum(2); + for (const auto& e : v) + sum = sum + e; + VERIFY(sum[0]==3); + VERIFY(sum[1]==3); +}
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