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libstdc++: Avoid aliasing violation in std::valarray [PR99117]

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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.
This commit is contained in:
Jonathan Wakely 2024-02-08 13:59:42 +00:00
parent 4d6513f80b
commit b58f0e5216
2 changed files with 24 additions and 1 deletions
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8
libstdc++-v3/include/std/valarray
View file

@ -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)

17
libstdc++-v3/testsuite/26_numerics/valarray/99117.cc Normal file
View file

@ -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);
}