[gcc r10-8928] libstdc++: Mark some more algorithms constexpr for C++20

[Patrick Palka]

https://gcc.gnu.org/g:f877f580a574491111ceac6f35b6ca6dd0a2585f

commit r10-8928-gf877f580a574491111ceac6f35b6ca6dd0a2585f
Author: Patrick Palka <ppalka@redhat.com>
Date:   Mon Sep 21 20:48:17 2020 -0400

    libstdc++: Mark some more algorithms constexpr for C++20
    
    As per P0202.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/stl_algo.h (for_each_n): Mark constexpr for C++20.
            (search): Likewise for the overload that takes a searcher.
            * testsuite/25_algorithms/for_each/constexpr.cc: Test constexpr
            std::for_each_n.
            * testsuite/25_algorithms/search/constexpr.cc: Test constexpr
            std::search overload that takes a searcher.
    
    (cherry picked from commit f017952d31ba8fa965106505bed5844cc1a63b4b)

Diff:
---
 libstdc++-v3/include/bits/stl_algo.h                       |  2 ++
 libstdc++-v3/testsuite/25_algorithms/for_each/constexpr.cc | 12 ++++++++++++
 libstdc++-v3/testsuite/25_algorithms/search/constexpr.cc   |  4 ++++
 3 files changed, 18 insertions(+)

diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index 778a14be97f..bfab5a06cda 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -3854,6 +3854,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
    *  If `__f` has a return value it is ignored.
   */
   template<typename _InputIterator, typename _Size, typename _Function>
+    _GLIBCXX20_CONSTEXPR
     _InputIterator
     for_each_n(_InputIterator __first, _Size __n, _Function __f)
     {
@@ -4273,6 +4274,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
    *  @return @p __searcher(__first,__last).first
   */
   template<typename _ForwardIterator, typename _Searcher>
+    _GLIBCXX20_CONSTEXPR
     inline _ForwardIterator
     search(_ForwardIterator __first, _ForwardIterator __last,
 	   const _Searcher& __searcher)
diff --git a/libstdc++-v3/testsuite/25_algorithms/for_each/constexpr.cc b/libstdc++-v3/testsuite/25_algorithms/for_each/constexpr.cc
index 1bece35a0d9..b3aca23eccc 100644
--- a/libstdc++-v3/testsuite/25_algorithms/for_each/constexpr.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/for_each/constexpr.cc
@@ -34,3 +34,15 @@ test()
 }
 
 static_assert(test());
+
+constexpr bool
+test_n()
+{
+  int tot = 0;
+  auto sum = [&total = tot](int i){ total += i; };
+  auto sum2 = std::for_each_n(ca0.begin(), std::size(ca0)-1, sum);
+
+  return tot == 55;
+}
+
+static_assert(test_n());
diff --git a/libstdc++-v3/testsuite/25_algorithms/search/constexpr.cc b/libstdc++-v3/testsuite/25_algorithms/search/constexpr.cc
index ba9437eced7..e34194cfc5d 100644
--- a/libstdc++-v3/testsuite/25_algorithms/search/constexpr.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/search/constexpr.cc
@@ -31,6 +31,10 @@ test()
 				 cam.begin(), cam.end(),
 				 std::equal_to<int>());
 
+  const auto outtt2
+    = std::search(ca0.begin(), ca0.end(),
+		  std::default_searcher(cam.begin(), cam.end()));
+
   return true;
 }