[Bug libstdc++/113807] [performance] bitset::set not using memset opportunity
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113807 --- Comment #8 from rhalbersma --- For bitset::operator==, I wonder why (at last in C++20 and later mode) it is not defaulted? For bitset::set and bitset::operator==, I also wonder why the manual loop vs memset/memcmp consteval logic is not delegated to a call of std::fill_n or std::equal, respectively? Then std::bitset is better proofed against future changes in the tradeoffs between manual loops, unrolled loops or library calls, no?
[Bug libstdc++/113807] [performance] bitset::set not using memset opportunity
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113807 --- Comment #3 from rhalbersma --- Nice that this is changed now. I noticed a similar optimization could be done for bitset::operator== (more accurately: the helper _M_is_equal) where there is an opportunity to use memcmp, with a similar dance for consteval contexts. MSVC STL also does this.
[Bug libstdc++/113807] New: [performance] bitset::set not using memset opportunity
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113807 Bug ID: 113807 Summary: [performance] bitset::set not using memset opportunity Product: gcc Version: 14.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: libstdc++ Assignee: unassigned at gcc dot gnu.org Reporter: rhalbersma at gmail dot com Target Milestone: --- Conditionally on is_constant_evaluated() being false, bitset::reset delegate to __builtin_memset(_M_w, 0, _Nw * sizeof(_WordT)) and uses a loop otherwise. In contrast, bitset::set unconditionally has a raw loop. Can't bitset::set also not similarly use __builtin_memset(_M_w, 0xFF, _Nw * sizeof(_WordT)); when is_constant_evaluated() is false?
[Bug libstdc++/113806] New: [performance] bitset::operator>>= unnecessarily sanitizes the high-word
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113806 Bug ID: 113806 Summary: [performance] bitset::operator>>= unnecessarily sanitizes the high-word Product: gcc Version: 14.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: libstdc++ Assignee: unassigned at gcc dot gnu.org Reporter: rhalbersma at gmail dot com Target Milestone: --- It seems that since time immemorial, bitset::operator>>= unnecessarily sanitizes the high word by calling this->_M_do_sanitize(); It is unnecessary since right-shifting moves bits away from the high-word so that the class invariant can not be violated (in contrast to bitset::operator<<= where bits flow into the high word, and where t). Current LOC is 1092 in on libstdc++ trunk, and could be removed with no functional change.
[Bug libstdc++/108260] New: __cpp_lib_ranges_zip feature test macro not defined while std::views::zip is supported
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108260 Bug ID: 108260 Summary: __cpp_lib_ranges_zip feature test macro not defined while std::views::zip is supported Product: gcc Version: 13.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: libstdc++ Assignee: unassigned at gcc dot gnu.org Reporter: rhalbersma at gmail dot com Target Milestone: --- I'm a happy user of std::views::zip in gcc-latest but AFAICS the feature test macro __cpp_lib_ranges_zip is not yet defined, neither in , , , nor in . This makes it hard #ifdedf my code on this feature. Just for my curiosity: is it generally the case that feature test macros are being added along with the feature completeness? Or should I condition my mixed C++20/C++23 code in another way?
[Bug c++/93480] Defaulted <=> doesn't expand array elements
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93480 --- Comment #9 from rhalbersma --- Could this fix also be back-ported to gcc 10?
[Bug c++/94924] Default equality operator for C-array compares addresses, not data
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94924 --- Comment #4 from rhalbersma --- Is there any chance that this bug fix can be backported to gcc 10 also?
[Bug c++/108214] New: writinng bitset to stringstream fails
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108214
Bug ID: 108214
Summary: writinng bitset to stringstream fails
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: rhalbersma at gmail dot com
Target Milestone: ---
#include
#include
int main() {
using T = std::bitset<1>;
T a(1);
T b;
std::stringstream sstr;
sstr << a;
sstr >> b;
}
The above program works correctly for g++ until version 12, but for version 13
(trunk) it errors out with: "terminate called after throwing an instance of
'std::invalid_argument' what(): bitset::_M_copy_from_ptr"
Godbolt link: https://godbolt.org/z/nnKT6cddb
