From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 2181) id F01723858D20; Sat, 6 Jan 2024 13:40:00 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org F01723858D20 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1704548401; bh=3zt7CHipevHTM/p7UQoijXo5tillTSaRumJn9YsZJi4=; h=From:To:Subject:Date:From; b=U0qkpTqzceXTjst+u0NIFeORyLsIelZEkSKTiixuBBM6vUrRbFKPLNTLfG3e7L1Qm ua/lKiPMIKdfUQ4WGLKTX2W8E6fVj3ENHuXDfacPN7dvPo8GyXfePtvCa/7pLgvjDu /W9wB08yyl04t28LDva4CtMymz5CyXVo2IN6iHAc= MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="utf-8" From: Jonathan Wakely To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r13-8193] libstdc++: Fix std::char_traits::move [PR113200] X-Act-Checkin: gcc X-Git-Author: Jonathan Wakely X-Git-Refname: refs/heads/releases/gcc-13 X-Git-Oldrev: 7eb3a32898bf70ab93b18aeaa6f5d2bba4c60a13 X-Git-Newrev: 22601c1c25652c71c8bab4707866c020d6dad79a Message-Id: <20240106134000.F01723858D20@sourceware.org> Date: Sat, 6 Jan 2024 13:40:00 +0000 (GMT) List-Id: https://gcc.gnu.org/g:22601c1c25652c71c8bab4707866c020d6dad79a commit r13-8193-g22601c1c25652c71c8bab4707866c020d6dad79a Author: Jonathan Wakely Date: Wed Jan 3 15:01:09 2024 +0000 libstdc++: Fix std::char_traits::move [PR113200] The current constexpr implementation of std::char_traits::move relies on being able to compare the pointer parameters, which is not allowed for unrelated pointers. We can use __builtin_constant_p to determine whether it's safe to compare the pointers directly. If not, then we know the ranges must be disjoint and so we can use char_traits::copy to copy forwards from the first character to the last. If the pointers can be compared directly, then we can simplify the condition for copying backwards to just two pointer comparisons. libstdc++-v3/ChangeLog: PR libstdc++/113200 * include/bits/char_traits.h (__gnu_cxx::char_traits::move): Use __builtin_constant_p to check for unrelated pointers that cannot be compared during constant evaluation. * testsuite/21_strings/char_traits/requirements/113200.cc: New test. (cherry picked from commit 15cc291887dc9dd92b2c93f4545e20eb6c190122) Diff: --- libstdc++-v3/include/bits/char_traits.h | 16 +++------------- .../21_strings/char_traits/requirements/113200.cc | 20 ++++++++++++++++++++ 2 files changed, 23 insertions(+), 13 deletions(-) diff --git a/libstdc++-v3/include/bits/char_traits.h b/libstdc++-v3/include/bits/char_traits.h index 68ed827f982..67f507538ca 100644 --- a/libstdc++-v3/include/bits/char_traits.h +++ b/libstdc++-v3/include/bits/char_traits.h @@ -227,19 +227,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION #if __cplusplus >= 202002L if (std::__is_constant_evaluated()) { - if (__s1 == __s2) // unlikely, but saves a lot of work - return __s1; - const auto __end = __s2 + __n - 1; - bool __overlap = false; - for (std::size_t __i = 0; __i < __n - 1; ++__i) - { - if (__s1 + __i == __end) - { - __overlap = true; - break; - } - } - if (__overlap) + // Use __builtin_constant_p to avoid comparing unrelated pointers. + if (__builtin_constant_p(__s2 < __s1) + && __s1 > __s2 && __s1 < (__s2 + __n)) { do { diff --git a/libstdc++-v3/testsuite/21_strings/char_traits/requirements/113200.cc b/libstdc++-v3/testsuite/21_strings/char_traits/requirements/113200.cc new file mode 100644 index 00000000000..0fe765d53bc --- /dev/null +++ b/libstdc++-v3/testsuite/21_strings/char_traits/requirements/113200.cc @@ -0,0 +1,20 @@ +// { dg-do compile { target c++20 } } + +// PR libstdc++/113200 +// char_traits::move is not constexpr when the argument is a string literal + +#include + +template struct S +{ + char data_[ N ]; + + constexpr S( char const* p ): data_{} + { + std::char_traits::move( data_, p, N ); + } +}; + +template S( char const(&)[N] ) -> S; + +constexpr S s( "test" );