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libstdc++: Fix std::lexicographic_compare for unsigned char (PR 93972)

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The new 25_algorithms/lexicographical_compare/93972.cc test fails on
targets where char is unsigned, revealing an existing regression with
the std::__memcmp helper that had gone unnoticed in
std::lexicographical_compare. When comparing char and unsigned char, the
memcmp optimisation is enabled, but the new std::__memcmp function fails
to compile for mismatched types.

	PR libstdc++/93972
	* include/bits/stl_algobase.h (__memcmp): Allow pointer types to
	differ.
	* testsuite/25_algorithms/lexicographical_compare/uchar.cc: New test.
This commit is contained in:
Jonathan Wakely 2020-03-02 17:03:28 +00:00
parent 4c39156340
commit d112e173ea
3 changed files with 71 additions and 2 deletions
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5
libstdc++-v3/ChangeLog
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@ -1,5 +1,10 @@
2020-03-02 Jonathan Wakely <jwakely@redhat.com>
PR libstdc++/93972
* include/bits/stl_algobase.h (__memcmp): Allow pointer types to
differ.
* testsuite/25_algorithms/lexicographical_compare/uchar.cc: New test.
* include/std/ranges (__detail::__maybe_empty_t): Rename to
__maybe_present_t.
(__adaptor::_RangeAdaptor, join_view, split_view): Use new name.

7
libstdc++-v3/include/bits/stl_algobase.h
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@ -84,11 +84,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* A constexpr wrapper for __builtin_memcmp.
* @param __num The number of elements of type _Tp (not bytes).
*/
template<typename _Tp>
template<typename _Tp, typename _Up>
_GLIBCXX14_CONSTEXPR
inline int
__memcmp(const _Tp* __first1, const _Tp* __first2, size_t __num)
__memcmp(const _Tp* __first1, const _Up* __first2, size_t __num)
{
#if __cplusplus >= 201103L
static_assert(sizeof(_Tp) == sizeof(_Up), "can be compared with memcmp");
#endif
#ifdef __cpp_lib_is_constant_evaluated
if (std::is_constant_evaluated())
{

61
libstdc++-v3/testsuite/25_algorithms/lexicographical_compare/uchar.cc Normal file
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@ -0,0 +1,61 @@
// Copyright (C) 2020 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING3. If not see
// <http://www.gnu.org/licenses/>.
// { dg-options "-fchar8_t" }
// { dg-do run }
#include <algorithm>
#include <testsuite_hooks.h>
// Check that the memcmp optimization in std::lexicographical_compare
// still works for mixed-type comparisons.
void
test01()
{
unsigned char a = 0;
char8_t b = 1;
VERIFY( std::lexicographical_compare(&a, &a + 1, &b, &b + 1) );
VERIFY( ! std::lexicographical_compare(&b, &b + 1, &a, &a + 1) );
}
void
test02()
{
// N.B. if char is signed this won't actually use the memcmp optimization.
unsigned char a = 0;
char b = 1;
VERIFY( std::lexicographical_compare(&a, &a + 1, &b, &b + 1) );
VERIFY( ! std::lexicographical_compare(&b, &b + 1, &a, &a + 1) );
}
void
test03()
{
// N.B. if char is signed this won't actually use the memcmp optimization.
char a = 0;
char8_t b = 1;
VERIFY( std::lexicographical_compare(&a, &a + 1, &b, &b + 1) );
VERIFY( ! std::lexicographical_compare(&b, &b + 1, &a, &a + 1) );
}
int main()
{
test01();
test02();
test03();
}