[libcxx-commits] [PATCH] D65721: Make rotate a constexpr

Louis Dionne via Phabricator via libcxx-commits libcxx-commits at lists.llvm.org
Mon Aug 5 09:30:28 PDT 2019

ldionne requested changes to this revision.
ldionne added inline comments.
This revision now requires changes to proceed.

Comment at: libcxx/include/algorithm:2308
 template <class _ForwardIterator>
 __rotate_left(_ForwardIterator __first, _ForwardIterator __last)
This function can be made constexpr in all standard modes that support generalized constexpr (so C++14 and above).

That holds for all helper functions below.

Comment at: libcxx/include/algorithm:2367
 __algo_gcd(_Integral __x, _Integral __y)

Comment at: libcxx/include/algorithm:2381
+_LIBCPP_CONSTEXPR_AFTER_CXX17 _RandomAccessIterator
 __rotate_gcd(_RandomAccessIterator __first, _RandomAccessIterator __middle, _RandomAccessIterator __last)

Comment at: libcxx/test/std/algorithms/alg.modifying.operations/alg.rotate/rotate.pass.cpp:425
+template<class Iter>
+constexpr bool test_constexr()
Typo: `test_constexpr`

Comment at: libcxx/test/std/algorithms/alg.modifying.operations/alg.rotate/rotate.pass.cpp:458
+#if TEST_STD_VER > 17
+    static_assert(test_constexr<forward_iterator<int*> >());
+    static_assert(test_constexr<bidirectional_iterator<int*> >());
It would be nice if we could run all the same tests for constexpr and non-constexpr. It's not clear to me why we can't just run `test<....>` in a constexpr context. As for `test1`, it allocates memory but it might be possible to change the test to avoid that?

Generally speaking, I'd like for us to develop a fairly mechanical way of testing things in a constexpr context, since we're going to have to do that for almost all of `<algorithm>`. I think it's important to have the same test coverage for constexpr and non-constexpr (whenever it makes sense, of course).

  rCXX libc++



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