libstdc++: Define std::lexicographical_compare_three_way for C++20

	* include/bits/stl_algobase.h (lexicographical_compare_three_way):
	Define for C++20.
	* testsuite/25_algorithms/lexicographical_compare_three_way/1.cc: New
	test.
	* testsuite/25_algorithms/lexicographical_compare_three_way/
	constexpr.cc: New test.

From-SVN: r278996

4 files changed, 302 insertions, 0 deletions

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 3bbf4253e66..a5ed14528df 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,5 +1,12 @@
 2019-12-05  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/bits/stl_algobase.h (lexicographical_compare_three_way):
+	Define for C++20.
+	* testsuite/25_algorithms/lexicographical_compare_three_way/1.cc: New
+	test.
+	* testsuite/25_algorithms/lexicographical_compare_three_way/
+	constexpr.cc: New test.
+
 	* python/libstdcxx/v6/printers.py (StdCmpCatPrinter): New printer.
 	* testsuite/libstdc++-prettyprinters/cxx20.cc: New test.
 
diff --git a/libstdc++-v3/include/bits/stl_algobase.h b/libstdc++-v3/include/bits/stl_algobase.h
index 98d324827ed..a2fd306e6d0 100644
--- a/libstdc++-v3/include/bits/stl_algobase.h
+++ b/libstdc++-v3/include/bits/stl_algobase.h
@@ -72,6 +72,9 @@
 #if __cplusplus >= 201103L
 # include <type_traits>
 #endif
+#if __cplusplus > 201703L
+# include <compare>
+#endif
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
@@ -1456,6 +1459,104 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
 	 __gnu_cxx::__ops::__iter_comp_iter(__comp));
     }
 
+#if __cpp_lib_three_way_comparison
+#if __cpp_lib_concepts
+  // Iter points to a contiguous range of unsigned narrow character type
+  // or std::byte, suitable for comparison by memcmp.
+  template<typename _Iter>
+    concept __is_byte_iter = contiguous_iterator<_Iter>
+      && __is_byte<iter_value_t<_Iter>>::__value != 0
+      && !__gnu_cxx::__numeric_traits<iter_value_t<_Iter>>::__is_signed;
+
+  // Return a struct with two members, initialized to the smaller of x and y
+  // (or x if they compare equal) and the result of the comparison x <=> y.
+  template<typename _Tp>
+    constexpr auto
+    __min_cmp(_Tp __x, _Tp __y)
+    {
+      struct _Res {
+	_Tp _M_min;
+	decltype(__x <=> __y) _M_cmp;
+      };
+      auto __c = __x <=> __y;
+      if (__c > 0)
+	return _Res{__y, __c};
+      return _Res{__x, __c};
+    }
+#endif
+
+  /**
+   *  @brief Performs dictionary comparison on ranges.
+   *  @ingroup sorting_algorithms
+   *  @param  __first1  An input iterator.
+   *  @param  __last1   An input iterator.
+   *  @param  __first2  An input iterator.
+   *  @param  __last2   An input iterator.
+   *  @param  __comp  A @link comparison_functors comparison functor@endlink.
+   *  @return   The comparison category that `__comp(*__first1, *__first2)`
+   *		returns.
+  */
+  template<typename _InputIter1, typename _InputIter2, typename _Comp>
+    constexpr auto
+    lexicographical_compare_three_way(_InputIter1 __first1,
+				      _InputIter1 __last1,
+				      _InputIter2 __first2,
+				      _InputIter2 __last2,
+				      _Comp __comp)
+    -> decltype(__comp(*__first1, *__first2))
+    {
+      // concept requirements
+      __glibcxx_function_requires(_InputIteratorConcept<_InputIter1>)
+      __glibcxx_function_requires(_InputIteratorConcept<_InputIter2>)
+      __glibcxx_requires_valid_range(__first1, __last1);
+      __glibcxx_requires_valid_range(__first2, __last2);
+
+#if __cpp_lib_concepts && __cpp_lib_is_constant_evaluated
+      using _Cat = decltype(__comp(*__first1, *__first2));
+      static_assert(same_as<common_comparison_category_t<_Cat>, _Cat>);
+
+      if (!std::is_constant_evaluated())
+	if constexpr (same_as<_Comp, __detail::_Synth3way>
+		      || same_as<_Comp, compare_three_way>)
+	  if constexpr (__is_byte_iter<_InputIter1>)
+	    if constexpr (__is_byte_iter<_InputIter2>)
+	      {
+		const auto [__len, __lencmp]
+		  = std::__min_cmp(__last1 - __first1, __last2 - __first2);
+		if (__len)
+		  {
+		    const auto __c
+		      = __builtin_memcmp(&*__first1, &*__first2, __len) <=> 0;
+		    if (__c != 0)
+		      return __c;
+		  }
+		return __lencmp;
+	      }
+#endif // concepts && is_constant_evaluated
+      while (__first1 != __last1 && __first2 != __last2)
+	{
+	  if (auto __cmp = __comp(*__first1, *__first2); __cmp != 0)
+	    return __cmp;
+	  ++__first1;
+	  ++__first2;
+	}
+      return __first1 != __last1 ? strong_ordering::greater
+	: __first2 != __last2 ? strong_ordering::less : strong_ordering::equal;
+    }
+
+  template<typename _InputIter1, typename _InputIter2>
+    constexpr auto
+    lexicographical_compare_three_way(_InputIter1 __first1,
+				      _InputIter1 __last1,
+				      _InputIter2 __first2,
+				      _InputIter2 __last2)
+    {
+      return std::lexicographical_compare_three_way(__first1, __last1,
+						    __first2, __last2,
+						    compare_three_way{});
+    }
+#endif // three_way_comparison
+
   template<typename _InputIterator1, typename _InputIterator2,
 	   typename _BinaryPredicate>
     _GLIBCXX20_CONSTEXPR
diff --git a/libstdc++-v3/testsuite/25_algorithms/lexicographical_compare_three_way/1.cc b/libstdc++-v3/testsuite/25_algorithms/lexicographical_compare_three_way/1.cc
new file mode 100644
index 00000000000..b1e70e80de7
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/lexicographical_compare_three_way/1.cc
@@ -0,0 +1,129 @@
+// 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/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <algorithm>
+#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+// Lambda that calls lexicographical_compare_three_way on two ranges.
+// Arguments are passed by value intentionally, so that a copy of the range
+// is traversed and the original is not modified. Otherwise when the range
+// has input iterators the range will be consumed after the first comparison.
+auto lexicomp3 = [](auto r1, auto r2) {
+  return std::lexicographical_compare_three_way(r1.begin(), r1.end(),
+						r2.begin(), r2.end());
+};
+
+void
+test01()
+{
+  using __gnu_test::test_container;
+  using __gnu_test::input_iterator_wrapper;
+  using __gnu_test::forward_iterator_wrapper;
+  int arr1[] = { 0, 1, 2, 3, 4, 5, 6, 7 };
+  int arr2[] = { 0, 1, 2, 3, 4, 5, 6, 777 };
+
+  {
+    test_container<int, input_iterator_wrapper> c1(arr1);
+    test_container<int, input_iterator_wrapper> c2(arr2);
+    VERIFY( lexicomp3(c1, c1) == 0 );
+    VERIFY( lexicomp3(c1, c2) < 0 );
+    VERIFY( lexicomp3(c2, c1) > 0 );
+  }
+
+  {
+    test_container<int, input_iterator_wrapper> c1(arr1, arr1+6);
+    test_container<int, input_iterator_wrapper> c2(arr2, arr2+6);
+    VERIFY( lexicomp3(c1, c1) == 0 );
+    VERIFY( lexicomp3(c1, c2) == 0 );
+    VERIFY( lexicomp3(c2, c1) == 0 );
+  }
+
+  {
+    test_container<int, input_iterator_wrapper> c1(arr1);
+    test_container<int, input_iterator_wrapper> c2(arr2, arr2+7);
+    VERIFY( lexicomp3(c1, c1) == 0 );
+    VERIFY( lexicomp3(c1, c2) > 0 );
+    VERIFY( lexicomp3(c2, c1) < 0 );
+  }
+
+  {
+    test_container<int, input_iterator_wrapper> c1(arr1);
+    test_container<int, forward_iterator_wrapper> c2(arr2);
+    VERIFY( lexicomp3(c1, c1) == 0 );
+    VERIFY( lexicomp3(c1, c2) < 0 );
+    VERIFY( lexicomp3(c2, c1) > 0 );
+  }
+
+  {
+    test_container<int, input_iterator_wrapper> c1(arr1);
+    test_container<int, forward_iterator_wrapper> c2(arr2, arr2+7);
+    VERIFY( lexicomp3(c1, c1) == 0 );
+    VERIFY( lexicomp3(c2, c2) == 0 );
+    VERIFY( lexicomp3(c1, c2) > 0 );
+    VERIFY( lexicomp3(c2, c1) < 0 );
+  }
+
+  {
+    test_container<int, forward_iterator_wrapper> c1(arr1, arr1+7);
+    test_container<int, input_iterator_wrapper> c2(arr2);
+    VERIFY( lexicomp3(c1, c1) == 0 );
+    VERIFY( lexicomp3(c2, c2) == 0 );
+    VERIFY( lexicomp3(c1, c2) < 0 );
+    VERIFY( lexicomp3(c2, c1) > 0 );
+  }
+}
+
+void
+test02()
+{
+  using __gnu_test::test_container;
+  using __gnu_test::input_iterator_wrapper;
+  using __gnu_test::forward_iterator_wrapper;
+  std::array<unsigned char, 8> c1 = { 0, 1, 2, 3, 4, 5, 6, 7 };
+  std::array<unsigned char, 8> c2 = { 0, 1, 2, 3, 4, 5, 6, 77 };
+
+  VERIFY( lexicomp3(c1, c1) == 0 );
+  VERIFY( lexicomp3(c1, c2) < 0 );
+  VERIFY( lexicomp3(c2, c1) > 0 );
+
+  std::array<unsigned char, 7> c3 = { 0, 1, 2, 3, 4, 5, 6 };
+  VERIFY( lexicomp3(c3, c3) == 0 );
+  VERIFY( lexicomp3(c1, c3) > 0 );
+  VERIFY( lexicomp3(c3, c1) < 0 );
+}
+
+void
+test03()
+{
+  unsigned char a[2] = { 1, 2 };
+  unsigned char* p = nullptr;
+  // ensure memcmp not called with nullptr
+  VERIFY( std::lexicographical_compare_three_way(p, p, a, a+2) < 0 );
+  VERIFY( std::lexicographical_compare_three_way(a, a+2, p, p) > 0 );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+  test03();
+}
diff --git a/libstdc++-v3/testsuite/25_algorithms/lexicographical_compare_three_way/constexpr.cc b/libstdc++-v3/testsuite/25_algorithms/lexicographical_compare_three_way/constexpr.cc
new file mode 100644
index 00000000000..5d1e15cc4f3
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/lexicographical_compare_three_way/constexpr.cc
@@ -0,0 +1,65 @@
+// 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/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <algorithm>
+
+constexpr bool
+test01(int i)
+{
+  int a1[] = { 0, 1, 2, 3, 4, 5, 6, i, 8 };
+  long a2[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8 };
+
+  return std::lexicographical_compare_three_way(a1, a1+0, a2, a2+0) == 0
+    && std::lexicographical_compare_three_way(a1, a1+9, a2, a2+9) == (i <=> 7)
+    && std::lexicographical_compare_three_way(a1, a1+7, a2, a2+7) == 0
+    && std::lexicographical_compare_three_way(a1, a1+8, a2, a2+7) > 0
+    && std::lexicographical_compare_three_way(a1, a1+7, a2, a2+8) < 0;
+}
+
+static_assert( test01(~7) );
+static_assert( test01(7) );
+static_assert( test01(8) );
+
+constexpr bool
+test02(unsigned char i)
+{
+  unsigned char a1[] = { 0, 1, 2, 3, 4, 5, 6, i, 8 };
+  unsigned char a2[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8 };
+
+  return std::lexicographical_compare_three_way(a1, a1+0, a2, a2+0) == 0
+    && std::lexicographical_compare_three_way(a1, a1+9, a2, a2+9) == (i <=> 7)
+    && std::lexicographical_compare_three_way(a1, a1+7, a2, a2+7) == 0
+    && std::lexicographical_compare_three_way(a1, a1+8, a2, a2+7) > 0
+    && std::lexicographical_compare_three_way(a1, a1+7, a2, a2+8) < 0;
+}
+
+static_assert( test02(248) );
+static_assert( test02(7) );
+static_assert( test02(8) );
+
+constexpr bool
+test03(unsigned char* p)
+{
+  unsigned char a[2] = { 1, 2 };
+  return std::lexicographical_compare_three_way(p, p, a, a+2) < 0
+    && std::lexicographical_compare_three_way(a, a+2, p, p) > 0;
+}
+
+static_assert( test03(nullptr) ); // ensure memcmp not called with nullptr