libstdc++: Move code after an early exit constexpr if to under an else branch

This avoids instantiating dead code when the true branch of the constexpr if is
taken.

libstdc++-v3/ChangeLog:

	* include/bits/ranges_algo.h (__lexicographical_compare_fn::operator()):
	Move code after an early exit constexpr if to under an else branch.
	* include/bits/ranges_algobase.h (__equal_fn::operator()): Likewise.

libstdc++-v3/ChangeLog

+2020-02-16  Patrick Palka  <ppalka@redhat.com>
+
+	* include/bits/ranges_algo.h (__lexicographical_compare_fn::operator()):
+	Move code after an early exit constexpr if to under an else branch.
+	* include/bits/ranges_algobase.h (__equal_fn::operator()): Likewise.
+
 2020-02-15  Patrick Palka  <ppalka@redhat.com>
 
 	* include/bits/ranges_algo.h: Adjust whitespace and formatting.

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

@@ -3318,7 +3318,8 @@ namespace ranges
 			 std::__niter_base(std::move(__last2)),
 			 std::move(__comp),
 			 std::move(__proj1), std::move(__proj2));
-
+	else
+	  {
 	    constexpr bool __sized_iters
 	      = (sized_sentinel_for<_Sent1, _Iter1>
 		 && sized_sentinel_for<_Sent2, _Iter2>);
@@ -3342,7 +3343,8 @@ namespace ranges
 		  {
 		    if (const auto __len = std::min(__d1, __d2))
 		      {
-		    const auto __c = std::__memcmp(__first1, __first2, __len);
+			const auto __c
+			  = std::__memcmp(__first1, __first2, __len);
 			if constexpr (is_same_v<_Comp, ranges::less>)
 			  {
 			    if (__c < 0)
@@ -3378,6 +3380,7 @@ namespace ranges
 	      }
 	    return __first1 == __last1 && __first2 != __last2;
 	  }
+      }
 
     template<input_range _Range1, input_range _Range2,
 	     typename _Proj1 = identity, typename _Proj2 = identity,

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

@@ -93,11 +93,8 @@ namespace ranges
 			 std::__niter_base(std::move(__last2)),
 			 std::move(__pred),
 			 std::move(__proj1), std::move(__proj2));
-
-	constexpr bool __sized_iters
-	  = (sized_sentinel_for<_Sent1, _Iter1>
-	     && sized_sentinel_for<_Sent2, _Iter2>);
-	if constexpr (__sized_iters)
+	else if constexpr (sized_sentinel_for<_Sent1, _Iter1>
+			   && sized_sentinel_for<_Sent2, _Iter2>)
 	  {
 	    auto __d1 = ranges::distance(__first1, __last1);
 	    auto __d2 = ranges::distance(__first2, __last2);