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* [gcc r10-9474] libstdc++: Fix up constexpr std::char_traits<char>::compare [PR99181]
@ 2021-03-19 23:29 Jakub Jelinek
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From: Jakub Jelinek @ 2021-03-19 23:29 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:311c57f6d8f285d69e44bf94152c753900cb1a0a
commit r10-9474-g311c57f6d8f285d69e44bf94152c753900cb1a0a
Author: Jakub Jelinek <jakub@redhat.com>
Date: Tue Feb 23 09:30:18 2021 +0100
libstdc++: Fix up constexpr std::char_traits<char>::compare [PR99181]
Because of LWG 467, std::char_traits<char>::lt compares the values
cast to unsigned char rather than char, so even when char is signed
we get unsigned comparision. std::char_traits<char>::compare uses
__builtin_memcmp and that works the same, but during constexpr evaluation
we were calling __gnu_cxx::char_traits<char_type>::compare. As
char_traits::lt is not virtual, __gnu_cxx::char_traits<char_type>::compare
used __gnu_cxx::char_traits<char_type>::lt rather than
std::char_traits<char>::lt and thus compared chars as signed if char is
signed.
This change fixes it by inlining __gnu_cxx::char_traits<char_type>::compare
into std::char_traits<char>::compare by hand, so that it calls the right
lt method.
2021-02-23 Jakub Jelinek <jakub@redhat.com>
PR libstdc++/99181
* include/bits/char_traits.h (char_traits<char>::compare): For
constexpr evaluation don't call
__gnu_cxx::char_traits<char_type>::compare but do the comparison loop
directly.
* testsuite/21_strings/char_traits/requirements/char/99181.cc: New
test.
(cherry picked from commit efa64fcce12074dd542670feb02eaee53e810a30)
Diff:
---
libstdc++-v3/include/bits/char_traits.h | 9 ++++-
.../char_traits/requirements/char/99181.cc | 40 ++++++++++++++++++++++
2 files changed, 48 insertions(+), 1 deletion(-)
diff --git a/libstdc++-v3/include/bits/char_traits.h b/libstdc++-v3/include/bits/char_traits.h
index c2267fa2823..b487476b092 100644
--- a/libstdc++-v3/include/bits/char_traits.h
+++ b/libstdc++-v3/include/bits/char_traits.h
@@ -349,7 +349,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
if (__builtin_constant_p(__n)
&& __constant_char_array_p(__s1, __n)
&& __constant_char_array_p(__s2, __n))
- return __gnu_cxx::char_traits<char_type>::compare(__s1, __s2, __n);
+ {
+ for (size_t __i = 0; __i < __n; ++__i)
+ if (lt(__s1[__i], __s2[__i]))
+ return -1;
+ else if (lt(__s2[__i], __s1[__i]))
+ return 1;
+ return 0;
+ }
#endif
return __builtin_memcmp(__s1, __s2, __n);
}
diff --git a/libstdc++-v3/testsuite/21_strings/char_traits/requirements/char/99181.cc b/libstdc++-v3/testsuite/21_strings/char_traits/requirements/char/99181.cc
new file mode 100644
index 00000000000..01a70da046c
--- /dev/null
+++ b/libstdc++-v3/testsuite/21_strings/char_traits/requirements/char/99181.cc
@@ -0,0 +1,40 @@
+// { dg-options "-std=gnu++17" }
+// { dg-do run { target c++17 } }
+
+// Copyright (C) 2021 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/>.
+
+#include <string>
+#include <testsuite_hooks.h>
+
+void test01()
+{
+ const char *a = "\x7f";
+ const char *b = "\x80";
+ int c = std::char_traits<char>::compare(a, b, 2);
+ constexpr int d = std::char_traits<char>::compare("\x7f", "\x80", 2);
+
+ VERIFY( c && (c < 0) == (static_cast<unsigned char>(a[0])
+ < static_cast<unsigned char>(b[0])) );
+ VERIFY( d && (c < 0) == (d < 0) );
+}
+
+int main()
+{
+ test01();
+ return 0;
+}
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