Test for C++20 p0858 - ConstexprIterator requirements.

Ed Smith-Rowland via libstdc++ libstdc++@gcc.gnu.org
Sat Jun 8 16:06:00 GMT 2019


On 6/7/19 11:42 AM, Jonathan Wakely wrote:
> On 01/06/19 15:40 -0400, Ed Smith-Rowland via libstdc++ wrote:
>> On 6/1/19 2:42 PM, Ville Voutilainen wrote:
>>> On Sat, 1 Jun 2019 at 21:09, Ed Smith-Rowland <3dw4rd@verizon.net> 
>>> wrote:
>>>> On 5/31/19 6:29 PM, Ville Voutilainen wrote:
>>>>> On Sat, 1 Jun 2019 at 01:24, Ed Smith-Rowland via libstdc++
>>>>> <libstdc++@gcc.gnu.org> wrote:
>>>>>> Greetings,
>>>>>>
>>>>>> Iterators for <array> and <string_view> are usabe in a constexpr 
>>>>>> context
>>>>>> since C++2017.
>>>>>>
>>>>>> This just adds a compile test to make sure and check a box for C++20
>>>>>> p0858 - ConstexprIterator requirements.
>>>>> Those tests don't use the iterators in a constexpr context. To do
>>>>> that, maybe do those std::copy operations
>>>>> in a constexpr function and then initialize a constexpr variable with
>>>>> the result of a call to that function?
>>>> Thanks Ville,
>>>>
>>>> I had completely forgotten to make these test functions constexpr - 
>>>> FIXED.
>>> .but that doesn't enforce a constexpr context. If you add another
>>> function that calls these functions
>>> and initializes a constexpr variable, then we have the enforcement I
>>> seek. Such as
>>>
>>> void test2()
>>> {
>>> ?????? constexpr char x = test();
>>> }
>>>
>> Ok, third time's a charm.
>>
>> I was brain dead about the constexpr patch.?? I'm now setting a 
>> constexpr variable from test() in a caller.
>>
>> But static_assert is a constexpr context no?
>>
>> Ed
>>
>>
>
>> 2019-06-03?? Edward Smith-Rowland <3dw4rd@verizon.net>
>>
>> ????????Test for C++20 p0858 - ConstexprIterator requirements.
>> ????????* 
>> testsuite/21_strings/basic_string_view/requirements/constexpr_iter.cc:
>> ????????New test.
>> ????????* testsuite/23_containers/array/requirements/constexpr_iter.cc:
>> ????????New test.
>>
>
>> Index: 
>> testsuite/21_strings/basic_string_view/requirements/constexpr_iter.cc
>> ===================================================================
>> --- 
>> testsuite/21_strings/basic_string_view/requirements/constexpr_iter.cc 
>> (nonexistent)
>> +++ 
>> testsuite/21_strings/basic_string_view/requirements/constexpr_iter.cc 
>> (working copy)
>> @@ -0,0 +1,43 @@
>> +// { dg-do compile { target c++2a } }
>
> Please check the testsuite/libstdc++.log or testsuite/libstdc++.sum
> files for the new tests. I expect they are both UNSUPPORTED.
>
> That's because you've given a target c++2a which means they won't be
> run unless a suitable -std option is given. And you haven't given one.
>
> You need to add { dg-options "-std=gnu++2a" } before the dg-do line.
>
> Also if the tests are restricted to C++2a then there's no point having
> the #if __cplusplus > 201703L check, because that will never be false.
>
I had supplied the option for gnu++2a by hand and they passed.?? They 
were not UNSUPPORTED.

I just added the dg-options (at very top) and reran the testsuite 
without fancy tricks (except for gnu++2a).

I also took out the #if __cplusplus.?? I was just playing around and 
discovered that these pass in C++17 if you comment out the C++20 
constexpr algos.

OK for trunk?

Also, we could declare victory for this for gcc-9.?? May I backport after 
this is in?

Ed


-------------- next part --------------
2019-06-10  Edward Smith-Rowland  <3dw4rd@verizon.net>

	Test for C++20 p0858 - ConstexprIterator requirements.
	* testsuite/21_strings/basic_string_view/requirements/constexpr_iter.cc:
	New test.
	* testsuite/23_containers/array/requirements/constexpr_iter.cc:
	New test.

-------------- next part --------------
Index: testsuite/21_strings/basic_string_view/requirements/constexpr_iter.cc
===================================================================
--- testsuite/21_strings/basic_string_view/requirements/constexpr_iter.cc	(nonexistent)
+++ testsuite/21_strings/basic_string_view/requirements/constexpr_iter.cc	(working copy)
@@ -0,0 +1,42 @@
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+//
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+#include <string_view>
+#include <array>
+
+constexpr char
+test()
+{
+  constexpr std::string_view hw("Hello, World!");
+  static_assert('H' == *hw.begin());
+  auto ch = hw[4];
+  static_assert('W' == *(hw.cbegin() + 7));
+
+  std::array<int, hw.size()> a2{{0,0,0,0,0,0,0,0,0,0,0,0,0}};
+  std::copy(hw.begin(), hw.end(), a2.begin());
+
+  return *(hw.cbegin() + 3);
+}
+
+void
+run_test()
+{
+  constexpr char ch = test();
+}
Index: testsuite/23_containers/array/requirements/constexpr_iter.cc
===================================================================
--- testsuite/23_containers/array/requirements/constexpr_iter.cc	(nonexistent)
+++ testsuite/23_containers/array/requirements/constexpr_iter.cc	(working copy)
@@ -0,0 +1,41 @@
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+//
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+#include <array>
+
+constexpr int
+test()
+{
+  constexpr std::array<int, 3> a1{{1, 2, 3}};
+  static_assert(1 == *a1.begin());
+  auto n = a1[0] * a1[1]* a1[2];
+  static_assert(1 == *a1.cbegin());
+
+  std::array<int, 3> a2{{0, 0, 0}};
+  std::copy(a1.begin(), a1.end(), a2.begin());
+
+  return n;
+}
+
+void
+run_test()
+{
+  constexpr int n = test();
+}


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