[libcxx-commits] [PATCH] D118940: [libc++] Fix std::__debug_less in c++17.

[Jordan Rupprecht via Phabricator via libcxx-commits]

rupprecht created this revision.
rupprecht requested review of this revision.
Herald added a reviewer: jdoerfert.
Herald added subscribers: libcxx-commits, sstefan1.
Herald added a project: libc++.
Herald added a reviewer: libc++.

b07b5bd72716625e0976a84d23652d94d8d0165a <https://reviews.llvm.org/rGb07b5bd72716625e0976a84d23652d94d8d0165a> adds a use of `__comp_ref_type.h` to `std::min`. When libc++ is built with `-D_LIBCPP_DEBUG=0`, this enables `std::__debug_less`, which is only marked constexpr after c++17.

`std::min` itself is marked as being `constexpr` as of c++14, so by extension, `std::__debug_less` should also be marked `constexpr` for the same versions so that `std::min` can use it. This change lowers the guard from `> 17` to `> 11`.

Reproducer in godbolt: https://godbolt.org/z/ans3TGsj8

  constexpr int x() { return std::min<int>({1, 2, 3, 4}); }
  
  static_assert(x() == 1);


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D118940

Files:
  libcxx/include/__algorithm/comp_ref_type.h
  libcxx/test/libcxx/algorithms/debug_less.pass.cpp


Index: libcxx/test/libcxx/algorithms/debug_less.pass.cpp
===================================================================
--- libcxx/test/libcxx/algorithms/debug_less.pass.cpp
+++ libcxx/test/libcxx/algorithms/debug_less.pass.cpp
@@ -270,7 +270,7 @@
     assert(dl(static_cast<int&&>(1), static_cast<const int&&>(2)));
 }
 
-#if TEST_STD_VER > 17
+#if TEST_STD_VER > 11
 constexpr bool test_constexpr() {
     std::less<> cmp{};
     __debug_less<std::less<> > dcmp(cmp);
@@ -287,7 +287,7 @@
     test_non_const_arg_cmp();
     test_value_iterator();
     test_value_categories();
-#if TEST_STD_VER > 17
+#if TEST_STD_VER > 11
     static_assert(test_constexpr(), "");
 #endif
     return 0;
Index: libcxx/include/__algorithm/comp_ref_type.h
===================================================================
--- libcxx/include/__algorithm/comp_ref_type.h
+++ libcxx/include/__algorithm/comp_ref_type.h
@@ -28,11 +28,11 @@
 struct __debug_less
 {
     _Compare &__comp_;
-    _LIBCPP_CONSTEXPR_AFTER_CXX17
+    _LIBCPP_CONSTEXPR_AFTER_CXX11
     __debug_less(_Compare& __c) : __comp_(__c) {}
 
     template <class _Tp, class _Up>
-    _LIBCPP_CONSTEXPR_AFTER_CXX17
+    _LIBCPP_CONSTEXPR_AFTER_CXX11
     bool operator()(const _Tp& __x,  const _Up& __y)
     {
         bool __r = __comp_(__x, __y);
@@ -42,7 +42,7 @@
     }
 
     template <class _Tp, class _Up>
-    _LIBCPP_CONSTEXPR_AFTER_CXX17
+    _LIBCPP_CONSTEXPR_AFTER_CXX11
     bool operator()(_Tp& __x,  _Up& __y)
     {
         bool __r = __comp_(__x, __y);
@@ -52,7 +52,7 @@
     }
 
     template <class _LHS, class _RHS>
-    _LIBCPP_CONSTEXPR_AFTER_CXX17
+    _LIBCPP_CONSTEXPR_AFTER_CXX11
     inline _LIBCPP_INLINE_VISIBILITY
     decltype((void)declval<_Compare&>()(
         declval<_LHS &>(), declval<_RHS &>()))
@@ -62,7 +62,7 @@
     }
 
     template <class _LHS, class _RHS>
-    _LIBCPP_CONSTEXPR_AFTER_CXX17
+    _LIBCPP_CONSTEXPR_AFTER_CXX11
     inline _LIBCPP_INLINE_VISIBILITY
     void __do_compare_assert(long, _LHS &, _RHS &) {}
 };


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