Tested x86_64-linux, pushed to gcc-10 branch.
-- >8 --
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.
---
libstdc++-v3/include/bits/list.tcc | 4 ++++
1 file changed, 4 insertions(+)
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
}
}
--
2.37.1
