[Bug libstdc++/113200] std::char_traits::move is not constexpr when the argument is a string literal
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113200 Jonathan Wakely changed: What|Removed |Added Resolution|--- |FIXED Status|NEW |RESOLVED --- Comment #13 from Jonathan Wakely --- Fixed for 12.4 and 13.3, thanks for the report.
[Bug libstdc++/113200] std::char_traits::move is not constexpr when the argument is a string literal
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113200 --- Comment #12 from GCC Commits --- The releases/gcc-12 branch has been updated by Jonathan Wakely : https://gcc.gnu.org/g:26a9e8cee4d20e5b08c0336439c8f69a2f06af1c commit r12-10090-g26a9e8cee4d20e5b08c0336439c8f69a2f06af1c Author: Jonathan Wakely Date: Wed Jan 3 15:01:09 2024 + 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)
[Bug libstdc++/113200] std::char_traits::move is not constexpr when the argument is a string literal
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113200 --- Comment #11 from GCC Commits --- The releases/gcc-13 branch has been updated by Jonathan Wakely : https://gcc.gnu.org/g:22601c1c25652c71c8bab4707866c020d6dad79a commit r13-8193-g22601c1c25652c71c8bab4707866c020d6dad79a Author: Jonathan Wakely Date: Wed Jan 3 15:01:09 2024 + 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)
[Bug libstdc++/113200] std::char_traits::move is not constexpr when the argument is a string literal
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113200 Jonathan Wakely changed: What|Removed |Added Target Milestone|--- |12.4
[Bug libstdc++/113200] std::char_traits::move is not constexpr when the argument is a string literal
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113200 --- Comment #10 from GCC Commits --- The master branch has been updated by Jonathan Wakely : https://gcc.gnu.org/g:15cc291887dc9dd92b2c93f4545e20eb6c190122 commit r14-6944-g15cc291887dc9dd92b2c93f4545e20eb6c190122 Author: Jonathan Wakely Date: Wed Jan 3 15:01:09 2024 + 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.
[Bug libstdc++/113200] std::char_traits::move is not constexpr when the argument is a string literal
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113200 Jiang An changed: What|Removed |Added CC||de34 at live dot cn --- Comment #9 from Jiang An --- (In reply to Peter Dimov from comment #3) > I think that the compiler is correct; string literal address comparisons > aren't constant expressions. Clang gives the same error: > https://godbolt.org/z/xPWEf4z63. This looks weird... It seems that `+"abc" == +"def"` is never unspecified (must be false, but Clang rejects it in constant evaluation), while `"abcd" + 1 == +"bcd"` is unspecified. It's unclear to me whether we can practically detect all kinds of unspecifiedness in pointer comparision involving string literals.
[Bug libstdc++/113200] std::char_traits::move is not constexpr when the argument is a string literal
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113200 --- Comment #8 from Jonathan Wakely --- (In reply to Jonathan Wakely from comment #7) > Why does GCC accept this reduced version, which is invalid for the same > reason as the original? Looks like PR 70248
[Bug libstdc++/113200] std::char_traits::move is not constexpr when the argument is a string literal
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113200
--- Comment #7 from Jonathan Wakely ---
Why does GCC accept this reduced version, which is invalid for the same reason
as the original?
#include
constexpr int N = 5;
struct S
{
char data_[ N ];
constexpr S( char const* p )
{
std::char_traits::move( data_, p, N );
}
};
constexpr S s( "test" );
Clang rejects it the same way.
[Bug libstdc++/113200] std::char_traits::move is not constexpr when the argument is a string literal
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113200 Jonathan Wakely changed: What|Removed |Added Component|c++ |libstdc++ Keywords|diagnostic |rejects-valid --- Comment #6 from Jonathan Wakely --- Although we should fix the libstdc++ problem first, then re-assign (or maybe file a separate bug for the FE diagnostic).
[Bug libstdc++/113200] std::char_traits::move is not constexpr when the argument is a string literal
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113200 --- Comment #4 from Peter Dimov --- I didn't notice your subsequent comment, sorry. :-)
[Bug libstdc++/113200] std::char_traits::move is not constexpr when the argument is a string literal
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113200 --- Comment #3 from Peter Dimov --- I think that the compiler is correct; string literal address comparisons aren't constant expressions. Clang gives the same error: https://godbolt.org/z/xPWEf4z63.
[Bug libstdc++/113200] std::char_traits::move is not constexpr when the argument is a string literal
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113200 Andrew Pinski changed: What|Removed |Added Component|c++ |libstdc++ --- Comment #2 from Andrew Pinski --- I take that back, clang provideds a better error message on why `&a == "string"` is not constexpr: ``` /opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/14.0.0/../../../../include/c++/14.0.0/bits/char_traits.h:230:13: note: comparison of addresses of literals has unspecified value 230 | if (__s1 == __s2) // unlikely, but saves a lot of work |^ ```
