On 17/09/18 19:57 +0200, Marc Glisse wrote:
On Mon, 17 Sep 2018, Jonathan Wakely wrote:
On 15/09/18 14:27 +0200, Marc Glisse wrote:
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 Glisse
Index: 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 }; }
Won't this fail to compile in C++98 mode?
"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."
Oh sorry, I just looked at the patch and replied without reading the
top bit.
Even with -Wsystem-headers I don't get a warning, I have to precompile
with -P -E then compile the result to get "warning: extended
initializer lists only available with -std=c++11 or -std=gnu++11".
OK for trunk then.
