libstdc++ Two simplifications for lexicographical_compare

	* include/bits/ranges_algo.h (__lexicographical_compare_fn): Declare
	variables in smaller scope and avoid calling ranges::distance when we
	know they are pointers. Remove statically-unreachable use of
	__builtin_unreachable().
	* include/bits/stl_algobase.h (__lexicographical_compare::__lc):
	Define inline.

libstdc++-v3/ChangeLog

 2020-02-26  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/bits/ranges_algo.h (__lexicographical_compare_fn): Declare
+	variables in smaller scope and avoid calling ranges::distance when we
+	know they are pointers. Remove statically-unreachable use of
+	__builtin_unreachable().
+	* include/bits/stl_algobase.h (__lexicographical_compare::__lc):
+	Define inline.
+
 	* include/std/ranges (__detail::__maybe_empty_t): Define new helper
 	alias.
 	(__detail::__maybe_const_t): Likewise.

libstdc++-v3/include/bits/ranges_algo.h

@@ -3464,9 +3464,6 @@ namespace ranges
 		 && sized_sentinel_for<_Sent2, _Iter2>);
 	    if constexpr (__sized_iters)
 	      {
-		auto __d1 = ranges::distance(__first1, __last1);
-		auto __d2 = ranges::distance(__first2, __last2);
-
 		using _ValueType1 = iter_value_t<_Iter1>;
 		using _ValueType2 = iter_value_t<_Iter2>;
 		constexpr bool __use_memcmp
@@ -3480,6 +3477,9 @@ namespace ranges
 		     && is_same_v<_Proj2, identity>);
 		if constexpr (__use_memcmp)
 		  {
+		    const auto __d1 = __last1 - __first1;
+		    const auto __d2 = __last2 - __first2;
+
 		    if (const auto __len = std::min(__d1, __d2))
 		      {
 			const auto __c
@@ -3498,10 +3498,8 @@ namespace ranges
 			    if (__c < 0)
 			      return false;
 			  }
-			else
-			  __builtin_unreachable();
 		      }
-		    return (__last1 - __first1 < __last2 - __first2);
+		    return __d1 < __d2;
 		  }
 	      }
 

libstdc++-v3/include/bits/stl_algobase.h

@@ -1254,21 +1254,16 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
     {
       template<typename _II1, typename _II2>
 	_GLIBCXX20_CONSTEXPR
-	static bool __lc(_II1, _II1, _II2, _II2);
+	static bool
+	__lc(_II1 __first1, _II1 __last1, _II2 __first2, _II2 __last2)
+	{
+	  using __gnu_cxx::__ops::__iter_less_iter;
+	  return std::__lexicographical_compare_impl(__first1, __last1,
+						     __first2, __last2,
+						     __iter_less_iter());
+	}
     };
 
-  template<bool _BoolType>
-    template<typename _II1, typename _II2>
-      _GLIBCXX20_CONSTEXPR
-      bool
-      __lexicographical_compare<_BoolType>::
-      __lc(_II1 __first1, _II1 __last1, _II2 __first2, _II2 __last2)
-      {
-	return std::__lexicographical_compare_impl(__first1, __last1,
-						   __first2, __last2,
-					__gnu_cxx::__ops::__iter_less_iter());
-      }
-
   template<>
     struct __lexicographical_compare<true>
     {