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| author | Jonathan Wakely <jwakely@redhat.com> | 2021-10-13 21:32:14 +0100 |
|---|---|---|
| committer | Jonathan Wakely <jwakely@redhat.com> | 2021-10-13 22:35:32 +0100 |
| commit | f874a13ca3870a56036a90758b0d41c8c217f4f7 (patch) | |
| tree | 98f33bb92f926dbb4381667b941e6f52645700c5 /libstdc++-v3 | |
| parent | ce55693604813c5be7d23260f1fd276cf5a48f8f (diff) | |
| download | gcc-f874a13ca3870a56036a90758b0d41c8c217f4f7.zip gcc-f874a13ca3870a56036a90758b0d41c8c217f4f7.tar.gz gcc-f874a13ca3870a56036a90758b0d41c8c217f4f7.tar.bz2 | |
libstdc++: Fix regression in memory use when constructing paths
The changes in r12-4381 were intended to reduce memory usage, but
replacing the __contiguous constant in __string_from_range with the new
__is_contiguous variable template caused a regression. The old code
checked is_pointer_v<decltype(std::__niter_base(__first))> but he new
code just checks is_pointer_v<_InputIterator>. This means that we no
longer recognise basic_string::iterator and vector::iterator as
contiguous, and so return a temporary basic_string instead of a
basic_string_view. This only affects C++17 mode, because the
std::contiguous_iterator concept is used in C++20 which gives the right
answer for __normal_iterator (and more types as well).
The fix is to specialize the new __is_contiguous variable template so it
is true for __normal_iterator<T*, C> specializations. The new partial
specializations are defined for C++20 too, because it should be cheaper
to match the partial specialization than to check whether the
std::contiguous_iterator concept is satisfied.
libstdc++-v3/ChangeLog:
* include/bits/fs_path.h (__detail::__is_contiguous): Add
partial specializations for pointers and __normal_iterator.
Diffstat (limited to 'libstdc++-v3')
| -rw-r--r-- | libstdc++-v3/include/bits/fs_path.h | 9 |
1 files changed, 8 insertions, 1 deletions
diff --git a/libstdc++-v3/include/bits/fs_path.h b/libstdc++-v3/include/bits/fs_path.h index 05db792..c51bfa3 100644 --- a/libstdc++-v3/include/bits/fs_path.h +++ b/libstdc++-v3/include/bits/fs_path.h @@ -158,9 +158,16 @@ namespace __detail constexpr bool __is_contiguous = std::contiguous_iterator<_Iter>; #else template<typename _Iter> - constexpr bool __is_contiguous = is_pointer_v<_Iter>; + constexpr bool __is_contiguous = false; #endif + template<typename _Tp> + constexpr bool __is_contiguous<_Tp*> = true; + + template<typename _Tp, typename _Seq> + constexpr bool + __is_contiguous<__gnu_cxx::__normal_iterator<_Tp*, _Seq>> = true; + #if !defined _GLIBCXX_FILESYSTEM_IS_WINDOWS && defined _GLIBCXX_USE_CHAR8_T // For POSIX treat char8_t sequences as char without encoding conversions. template<typename _EcharT> |