Hello,
as explained in the PR, the implementation of vector<bool> is weirdly
wasteful. Preserving the ABI prevents from changing much for now, but this
small tweak can help the compiler remove quite a bit of dead code.
I think most other direct uses of _M_start are in constructors where the
offset has just been initialized to 0, so the compiler should already know
enough there, but I may have missed a few relevant places where the same
idea could be used.
I used C++11 syntax because I find it nicer, and the compiler accepts it
in C++98 mode with just a warning, suppressed in a standard header.
Bootstrap+regtest on powerpc64le-unknown-linux-gnu.
2018-09-15 Marc Glisse <marc.gli...@inria.fr>
PR libstdc++/87258
* include/bits/stl_bvector.h (vector::begin(), vector::cbegin()):
Rebuild _M_start with an explicit 0 offset.
--
Marc GlisseIndex: include/bits/stl_bvector.h
===================================================================
--- include/bits/stl_bvector.h (revision 264178)
+++ include/bits/stl_bvector.h (working copy)
@@ -802,25 +802,25 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
#endif
#if __cplusplus >= 201103L
void
assign(initializer_list<bool> __l)
{ _M_assign_aux(__l.begin(), __l.end(), random_access_iterator_tag()); }
#endif
iterator
begin() _GLIBCXX_NOEXCEPT
- { return this->_M_impl._M_start; }
+ { return { this->_M_impl._M_start._M_p, 0 }; }
const_iterator
begin() const _GLIBCXX_NOEXCEPT
- { return this->_M_impl._M_start; }
+ { return { this->_M_impl._M_start._M_p, 0 }; }
iterator
end() _GLIBCXX_NOEXCEPT
{ return this->_M_impl._M_finish; }
const_iterator
end() const _GLIBCXX_NOEXCEPT
{ return this->_M_impl._M_finish; }
reverse_iterator
@@ -835,21 +835,21 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
rend() _GLIBCXX_NOEXCEPT
{ return reverse_iterator(begin()); }
const_reverse_iterator
rend() const _GLIBCXX_NOEXCEPT
{ return const_reverse_iterator(begin()); }
#if __cplusplus >= 201103L
const_iterator
cbegin() const noexcept
- { return this->_M_impl._M_start; }
+ { return { this->_M_impl._M_start._M_p, 0 }; }
const_iterator
cend() const noexcept
{ return this->_M_impl._M_finish; }
const_reverse_iterator
crbegin() const noexcept
{ return const_reverse_iterator(end()); }
const_reverse_iterator
