From: Jonathan Wakely <jwakely@redhat.com>
To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org
Subject: [committed] libstdc++: Fix regression in std::stable_sort
Date: Wed, 24 Aug 2022 15:33:39 +0100 [thread overview]
Message-ID: <20220824143339.121092-1-jwakely@redhat.com> (raw)
Tested powerpc64le-linux, pushed to trunk.
No backport needed as the regression is only on trunk.
-- >8 --
The recent change to split out the cold path of std::stable_sort caused
a regression for some Qt code. The problem is that the library now adds
a value of type ptrdiff_t to the iterator, which is ambiguous with
-pedantic. The addition could either convert the iterator to a built-in
pointer and add the ptrdiff_t to that, or it could convert the ptrdiff_t
to the iterator's difference_type and use the iterator's own operator+.
The fix is to cast the ptrdiff_t value to the difference type first.
libstdc++-v3/ChangeLog:
* include/bits/stl_algo.h (__stable_sort): Cast size to
iterator's difference type.
* testsuite/25_algorithms/stable_sort/4.cc: New test.
---
libstdc++-v3/include/bits/stl_algo.h | 5 +-
.../testsuite/25_algorithms/stable_sort/4.cc | 51 +++++++++++++++++++
2 files changed, 54 insertions(+), 2 deletions(-)
create mode 100644 libstdc++-v3/testsuite/25_algorithms/stable_sort/4.cc
diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index c6078054514..57fa1c1dc55 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -5026,8 +5026,9 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
_TmpBuf __buf(__first, (__last - __first + 1) / 2);
if (__builtin_expect(__buf.requested_size() == __buf.size(), true))
- std::__stable_sort_adaptive(__first, __first + __buf.size(), __last,
- __buf.begin(), __comp);
+ std::__stable_sort_adaptive(__first,
+ __first + _DistanceType(__buf.size()),
+ __last, __buf.begin(), __comp);
else if (__builtin_expect(__buf.begin() == 0, false))
std::__inplace_stable_sort(__first, __last, __comp);
else
diff --git a/libstdc++-v3/testsuite/25_algorithms/stable_sort/4.cc b/libstdc++-v3/testsuite/25_algorithms/stable_sort/4.cc
new file mode 100644
index 00000000000..b7bda4eeaca
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/stable_sort/4.cc
@@ -0,0 +1,51 @@
+// { dg-options "-pedantic" }
+// { dg-do compile }
+
+#include <algorithm>
+
+/* This type is reduced from QTypedArrayData::iterator which has an implicit
+ * conversion to its pointer type and a difference type of int.
+ * The expression Iter() + ptrdiff_t(0) is ambiguous with -pedantic because it
+ * could either convert the RHS to int and use Iter::operator+(int)
+ * or it could convert the LHS to pointer and use built-in pointer arithmetic.
+ */
+struct Iter
+{
+ struct value_type { bool operator<(value_type) const; };
+ typedef value_type* pointer;
+ typedef value_type& reference;
+ typedef std::random_access_iterator_tag iterator_category;
+ typedef int difference_type;
+
+ reference operator*() const;
+ pointer operator->() const;
+
+ reference operator[](difference_type) const;
+
+ Iter& operator++();
+ Iter& operator--();
+ Iter operator++(int);
+ Iter operator--(int);
+
+ Iter& operator+=(difference_type);
+ Iter& operator-=(difference_type);
+
+ Iter operator+(difference_type) const;
+ Iter operator-(difference_type) const;
+
+ difference_type operator-(Iter) const;
+
+ operator pointer() const; // XXX this causes the ambiguity
+
+ bool operator==(Iter) const;
+ bool operator!=(Iter) const;
+
+ bool operator<(Iter) const;
+};
+
+Iter operator+(Iter::difference_type, Iter);
+
+int main()
+{
+ std::stable_sort(Iter(), Iter());
+}
--
2.37.2
reply other threads:[~2022-08-24 14:33 UTC|newest]
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