[v3] Implement C++17 GB50 resolution

Tested on Linux-x64

Implementation of resolution for C++17 GB50

2017-02-12 Dinka Ranns <dinka.ranns@googlemail.com>

        C++17 GB50 resolution
        * libstdc++-v3/include/std/chrono:
        (duration::operator++()): Add constexpr.
        (duration::operator++(int)): Likewise
        (duration::operator--()): Likewise
        (duration::operator--(int)): Likewise
        (duration::operator+=(const duration&)): Likewise
        (duration::operator-=(const duration&)): Likewise
        (duration::operator*=(const rep&)): Likewise
        (duration::operator/=(const rep&)): Likewise
        (duration::operator%=(const rep&)): Likewise
        (duration::operator%=(const duration&)): Likewise
        (time_point::operator+=(const duration&)): Likewise
        (time_point::operator-=(const duration&)): Likewise

        * libstdc++-v3/testsuite/20_util/duration/arithmetic/constexpr.cc:
new tests
        * libstdc++-v3/testsuite/20_util/time_point/arithmetic/constexpr.cc: new

On 14 February 2017 at 23:22, Dinka Ranns <dinka.ranns@googlemail.com> wrote:
>         C++17 GB50 resolution
>         * libstdc++-v3/include/std/chrono:

Pardon me for not noticing this while looking at the earlier versions
of this patch, but these should
not include the libstdc++-v3 prefix, so it should be

* include/std/chrono:

>         * libstdc++-v3/testsuite/20_util/duration/arithmetic/constexpr.cc:

And this should be

* testsuite/20_util/duration/arithmetic/constexpr.cc:

>         * libstdc++-v3/testsuite/20_util/time_point/arithmetic/constexpr.cc: new

and likewise here,

* testsuite/20_util/time_point/arithmetic/constexpr.cc: new

That's minor and can be fixed by a maintainer committing the patch,
but for future reference.

Hi, Dinka, thanks for the patch.

On 14/02/17 21:22 +0000, Dinka Ranns wrote:
>diff --git a/libstdc++-v3/include/std/chrono b/libstdc++-v3/include/std/chrono
>index ceae7f8..6a6995c 100644
>--- a/libstdc++-v3/include/std/chrono
>+++ b/libstdc++-v3/include/std/chrono
>@@ -349,50 +349,50 @@ _GLIBCXX_END_NAMESPACE_VERSION
> 	operator-() const
> 	{ return duration(-__r); }
>
>-	duration&
>+	constexpr duration&

This needs to use _GLIBCXX17_CONSTEXPR instead of 'constexpr'

These functions aren't constexpr in C++11 and C++14, and the standard
(annoyingly) forbids us from adding constexpr anywhere it isn't
present in the standard.

The macro _GLIBCXX17_CONSTEXPR expands to 'constexpr' if __cplusplus >
201402L, and expands to nothing otherwise.

Each new 'constexpr' you've added needs to use that macro.

>diff --git a/libstdc++-v3/testsuite/20_util/duration/arithmetic/constexpr.cc b/libstdc++-v3/testsuite/20_util/duration/arithmetic/constexpr.cc
>index 285f941..1128a52 100644
>--- a/libstdc++-v3/testsuite/20_util/duration/arithmetic/constexpr.cc
>+++ b/libstdc++-v3/testsuite/20_util/duration/arithmetic/constexpr.cc
>@@ -19,11 +19,31 @@
>
> #include <chrono>
> #include <testsuite_common_types.h>

There should be a blank line before and after this function, however
...

>+constexpr auto test_operators()
>+{
>+  std::chrono::nanoseconds d1 { };
>+  d1++;

This new function uses C++14 return type deduction, so will fail if
the test is run in C++11 mode (the default is C++14, but it can be
overridden on the command-line).

>+  ++d1;
>+  d1--;
>+  --d1;

Also once you change the new 'constexpr' specifiers to use the
_GLIBCXX17_CONSTEXPR macro this test will fail in C++14 mode. I think
this new function needs to be moved to a new test file, such as
testsuite/20_util/duration/arithmetic/constexpr_c++17.cc

That should contain just your new test_operators() function, because
the rest of the class will be tested by the existing constexpr.cc test
file. So something like:

// { dg-options "-std=gnu++17" }
// { dg-do compile { target c++1z } }

// Copyright etc. etc.
// ...

#include <chrono>

constexpr auto test_operators()
{
  // ...
}

constexpr auto d4 = test_operators();


Note that the "dg-do compile" line should use the c++1z target instead
of c++11, and needs to override the default dialect with a dg-options
line.

This test doesn't need a "main" function because it's a "dg-do
compile" test, so isn't linked. (The existing test that you modified
didn't need one either, but it doesn't do any harm leaving it there).


>diff --git a/libstdc++-v3/testsuite/20_util/time_point/arithmetic/constexpr.cc b/libstdc++-v3/testsuite/20_util/time_point/arithmetic/constexpr.cc
>new file mode 100644
>index 0000000..e87a226
>--- /dev/null
>+++ b/libstdc++-v3/testsuite/20_util/time_point/arithmetic/constexpr.cc
>@@ -0,0 +1,39 @@
>+// { dg-do compile { target c++11 } }

Since the time_point member functions will only be constexpr in C++17
this test also needs to use c++1z instead of c++11, and needs to
override the default C++14 dialect, i.e.

// { dg-options "-std=gnu++17" }
// { dg-do compile { target c++1z } }