Re: [committed] libstdc++: Avoid redundant checks in std::use_facet [PR103755]

[Stephan Bergmann <sbergman@redhat.com>]

On 11/11/22 06:30, Jonathan Wakely via Gcc-patches wrote:
> As discussed in the PR, this makes it three times faster to construct
> iostreams objects.
> 
> Tested x86_64-linux. Pushed to trunk.

I haven't yet tried to track down what's going on, but with various 
versions of Clang (e.g. clang-15.0.4-1.fc37.x86_64):

> $ cat test.cc
> #include <regex>
> int main(int, char ** argv) {
>     std::regex_traits<char>().transform(argv[0], argv[0] + 1);
> }

> $ clang++ --gcc-toolchain=... -fsanitize=undefined -O2 test.cc
> /usr/bin/ld: /tmp/test-c112b1.o: in function `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > std::__cxx11::regex_traits<char>::transform<char*>(char*, char*) const':
> test.cc:(.text._ZNKSt7__cxx1112regex_traitsIcE9transformIPcEENS_12basic_stringIcSt11char_traitsIcESaIcEEET_S9_[_ZNKSt7__cxx1112regex_traitsIcE9transformIPcEENS_12basic_stringIcSt11char_traitsIcESaIcEEET_S9_]+0x1b): undefined reference to `std::__cxx11::collate<char> const* std::__try_use_facet<std::__cxx11::collate<char> >(std::locale const&)'
> clang-15: error: linker command failed with exit code 1 (use -v to see invocation)