MSVSphere Packaging Team
6 months ago
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commit 6f5dcea85a31845ec6f4b6886734b0f02e013718
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Author: Jonathan Wakely <jwakely@redhat.com>
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Date: Tue Feb 27 17:50:34 2024 +0000
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libstdc++: Fix conditions for using memcmp in std::lexicographical_compare_three_way [PR113960]
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The change in r11-2981-g2f983fa69005b6 meant that
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std::lexicographical_compare_three_way started to use memcmp for
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unsigned integers on big endian targets, but for that to be valid we
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need the two value types to have the same size and we need to use that
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size to compute the length passed to memcmp.
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I already defined a __is_memcmp_ordered_with trait that does the right
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checks, std::lexicographical_compare_three_way just needs to use it.
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libstdc++-v3/ChangeLog:
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PR libstdc++/113960
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* include/bits/stl_algobase.h (__is_byte_iter): Replace with ...
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(__memcmp_ordered_with): New concept.
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(lexicographical_compare_three_way): Use __memcmp_ordered_with
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instead of __is_byte_iter. Use correct length for memcmp.
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* testsuite/25_algorithms/lexicographical_compare_three_way/113960.cc:
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New test.
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(cherry picked from commit f5cdda8acb06c20335855ed353ab9a441c12128a)
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diff --git a/libstdc++-v3/include/bits/stl_algobase.h b/libstdc++-v3/include/bits/stl_algobase.h
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index 7664301a208..6e648e48ad0 100644
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--- a/libstdc++-v3/include/bits/stl_algobase.h
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+++ b/libstdc++-v3/include/bits/stl_algobase.h
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@@ -1780,11 +1780,14 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
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}
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#if __cpp_lib_three_way_comparison
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- // Iter points to a contiguous range of unsigned narrow character type
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- // or std::byte, suitable for comparison by memcmp.
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- template<typename _Iter>
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- concept __is_byte_iter = contiguous_iterator<_Iter>
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- && __is_memcmp_ordered<iter_value_t<_Iter>>::__value;
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+ // Both iterators refer to contiguous ranges of unsigned narrow characters,
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+ // or std::byte, or big-endian unsigned integers, suitable for comparison
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+ // using memcmp.
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+ template<typename _Iter1, typename _Iter2>
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+ concept __memcmp_ordered_with
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+ = (__is_memcmp_ordered_with<iter_value_t<_Iter1>,
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+ iter_value_t<_Iter2>>::__value)
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+ && contiguous_iterator<_Iter1> && contiguous_iterator<_Iter2>;
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// Return a struct with two members, initialized to the smaller of x and y
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// (or x if they compare equal) and the result of the comparison x <=> y.
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@@ -1834,20 +1837,20 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
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if (!std::__is_constant_evaluated())
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if constexpr (same_as<_Comp, __detail::_Synth3way>
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|| same_as<_Comp, compare_three_way>)
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- if constexpr (__is_byte_iter<_InputIter1>)
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- if constexpr (__is_byte_iter<_InputIter2>)
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- {
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- const auto [__len, __lencmp] = _GLIBCXX_STD_A::
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- __min_cmp(__last1 - __first1, __last2 - __first2);
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- if (__len)
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- {
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- const auto __c
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- = __builtin_memcmp(&*__first1, &*__first2, __len) <=> 0;
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- if (__c != 0)
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- return __c;
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- }
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- return __lencmp;
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- }
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+ if constexpr (__memcmp_ordered_with<_InputIter1, _InputIter2>)
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+ {
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+ const auto [__len, __lencmp] = _GLIBCXX_STD_A::
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+ __min_cmp(__last1 - __first1, __last2 - __first2);
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+ if (__len)
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+ {
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+ const auto __blen = __len * sizeof(*__first1);
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+ const auto __c
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+ = __builtin_memcmp(&*__first1, &*__first2, __blen) <=> 0;
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+ if (__c != 0)
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+ return __c;
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+ }
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+ return __lencmp;
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+ }
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while (__first1 != __last1)
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{
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diff --git a/libstdc++-v3/testsuite/25_algorithms/lexicographical_compare_three_way/113960.cc b/libstdc++-v3/testsuite/25_algorithms/lexicographical_compare_three_way/113960.cc
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new file mode 100644
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index 00000000000..d51ae1a3d50
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--- /dev/null
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+++ b/libstdc++-v3/testsuite/25_algorithms/lexicographical_compare_three_way/113960.cc
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@@ -0,0 +1,15 @@
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+// { dg-do run { target c++20 } }
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+
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+// PR libstdc++/113960
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+// std::map with std::vector as input overwrites itself with c++20, on s390x
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+
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+#include <algorithm>
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+#include <testsuite_hooks.h>
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+
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+int main()
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+{
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+ unsigned short a1[] { 1, 2, 3 };
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+ unsigned short a2[] { 1, 2, 4 };
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+ // Incorrect memcmp comparison for big endian targets.
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+ VERIFY( std::lexicographical_compare_three_way(a1, a1+3, a2, a2+3) < 0 );
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+}
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