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* [gcc r13-8334] libstdc++: Avoid aliasing violation in std::valarray [PR99117]
@ 2024-02-16 15:12 Jonathan Wakely
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From: Jonathan Wakely @ 2024-02-16 15:12 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:3a72c717b311ce8093042d927a1f2f2b940a969c
commit r13-8334-g3a72c717b311ce8093042d927a1f2f2b940a969c
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.
(cherry picked from commit b58f0e5216a3053486e7f1aa96c3f2443b14d630)
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 f172db6c623e..ddf10b993da8 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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