Re: [PATCH] PR78991 make __gnu_cxx::__ops constructors explicit

[Jonathan Wakely <jwakely at redhat dot com>]

On 09/01/17 10:47 +0000, Jonathan Wakely wrote:
> On 09/01/17 10:39 +0000, Kyrill Tkachov wrote:
> > Hi Jonathan,
> >
> > On 06/01/17 12:40, Jonathan Wakely wrote:
> > > This solves a problem when using libstdc++ with Clang, due to Clang
> > > more eagerly instantiating constexpr function templates during
> > > argument deduction. G++ has some shortcuts to avoid this problem, but
> > > Clang doesn't, and it's not clear that it's strictly speaking a bug in
> > > Clang or if it's following the standard. By making these constructors
> > > explicit we stop them being considered by overload resolution for
> > > copying these functors, which stops us ending up back in the
> > > std::function SFINAE checks.
> > >
> > > I'm also using _GLIBCXX_MOVE to turn some internal copies into moves,
> > > because otherwise using something like std::function with <algorithm>
> > > results in a number of potentially expensive copies.
> > >
> > >   PR libstdc++/78991
> > >   * include/bits/predefined_ops.h (_Iter_comp_iter, _Iter_comp_val)
> > >   (_Val_comp_iter, _Iter_equals_val, _Iter_pred, _Iter_comp_to_val)
> > >   (_Iter_comp_to_iter, _Iter_negate): Make constructors explicit and
> > >   move function objects.
> > >   (__iter_comp_iter, __iter_comp_val, __val_comp_iter, __pred_iter)
> > >   (__iter_comp_val, __iter_comp_iter, __negate): Move function objects.
> > >   * testsuite/25_algorithms/sort/78991.cc: New test.
> > >
> > > Tested powerpc64le-linux, committed to trunk.
> > >
> > > I'll backport  the 'explicit' constructors (but not the _GLIBCXX_MOVE
> > > changes) to the branches too.
> >
> > I see this test fail on the GCC 5 branch on arm and aarch64 (error message pasted below).
> > Does the test need a gnu++11 guard or something on the branch?
>
> I thought I'd changed that before committing, I'll fix it.

Committed to gcc-5-branch.

commit 366c9e60ffa0536ab87de4e70ec807c2eb5fb66b
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Jan 9 10:54:44 2017 +0000

    Add missing dg-options to C++14 test
    
    	* testsuite/25_algorithms/sort/78991.cc: Compile with -std=gnu++14.

diff --git a/libstdc++-v3/testsuite/25_algorithms/sort/78991.cc b/libstdc++-v3/testsuite/25_algorithms/sort/78991.cc
index d947538..260878e 100644
--- a/libstdc++-v3/testsuite/25_algorithms/sort/78991.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/sort/78991.cc
@@ -15,6 +15,7 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
+// { dg-options "-std=gnu++14" }
 // { dg-do compile }
 
 // PR 78991