diff options
| author | Jonathan Wakely <jwakely@redhat.com> | 2021-09-29 20:46:55 +0100 |
|---|---|---|
| committer | Jonathan Wakely <jwakely@redhat.com> | 2022-08-03 11:50:08 +0100 |
| commit | f05b125a8d788a84dc7361b52f54af6169ad8b32 (patch) | |
| tree | 409dd6dd891251f85ac9595bed281326aa07173c /libstdc++-v3 | |
| parent | d1b51c15312940779b1288b59973d88b9592dd23 (diff) | |
libstdc++: Avoid try-catch and O(N) size in std::list::merge for old ABI
The current std::list::merge code calls size() before starting to merge
any elements, so that the _M_size members can be updated after the merge
finishes. The work is done in a try-block so that the sizes can still be
updated in an exception handler if any element comparison throws.
The _M_size members only exist for the cxx11 ABI, so the initial call to
size() and the try-catch are only needed for that ABI. For the old ABI
the size() call performs an O(N) list traversal to get a value that
isn't even used, and catching exceptions just to rethrow them isn't
needed either.
In r11-10123 this code was refactored to use an RAII guard type, but for
the gcc-10 branch a less invasive change using preprocessor conditionals
seems more appropriate.
libstdc++-v3/ChangeLog:
* include/bits/list.tcc (list::merge) [!USE_CXX11_ABI]: Remove
call to size() and try-catch block.
Diffstat (limited to 'libstdc++-v3')
| -rw-r--r-- | libstdc++-v3/include/bits/list.tcc | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/libstdc++-v3/include/bits/list.tcc b/libstdc++-v3/include/bits/list.tcc index ce9e983c539..1f27d8b786a 100644 --- a/libstdc++-v3/include/bits/list.tcc +++ b/libstdc++-v3/include/bits/list.tcc @@ -406,8 +406,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER iterator __last1 = end(); iterator __first2 = __x.begin(); iterator __last2 = __x.end(); +#if _GLIBCXX_USE_CXX11_ABI const size_t __orig_size = __x.size(); __try { +#endif while (__first1 != __last1 && __first2 != __last2) if (*__first2 < *__first1) { @@ -422,6 +424,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER this->_M_inc_size(__x._M_get_size()); __x._M_set_size(0); +#if _GLIBCXX_USE_CXX11_ABI } __catch(...) { @@ -430,6 +433,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER __x._M_set_size(__dist); __throw_exception_again; } +#endif } } |