[PATCH 2/1] libstdc++: Non-triv-copyable extra args aren't simple [PR100940]

[Patrick Palka]

This force-enables perfect forwarding call wrapper semantics whenever
the extra arguments of a partially applied range adaptor aren't all
trivially copyable, so as to avoid incurring unnecessary copies of
potentially expensive-to-copy objects (such as std::function objects)
when invoking the adaptor.

Tested on x86_64-pc-linux-gnu, does this look OK for trunk/11?

	PR libstdc++/100940

libstdc++-v3/ChangeLog:

	* include/std/ranges (__adaptor::__adaptor_has_simple_extra_args): Also
	require that the extra arguments are trivially copyable.
	* testsuite/std/ranges/adaptors/100577.cc (test04): New test.
---
 libstdc++-v3/include/std/ranges               |  6 ++++--
 .../testsuite/std/ranges/adaptors/100577.cc   | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 856975c6934..e858df88088 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -818,8 +818,10 @@ namespace views::__adaptor
   // True if the behavior of the range adaptor non-closure _Adaptor is
   // independent of the value category of its extra arguments _Args.
   template<typename _Adaptor, typename... _Args>
-    concept __adaptor_has_simple_extra_args = _Adaptor::_S_has_simple_extra_args
-      || _Adaptor::template _S_has_simple_extra_args<_Args...>;
+    concept __adaptor_has_simple_extra_args
+      = (_Adaptor::_S_has_simple_extra_args
+	 || _Adaptor::template _S_has_simple_extra_args<_Args...>)
+	&& (is_trivially_copyable_v<_Args> && ...);
 
   // A range adaptor closure that represents partial application of
   // the range adaptor _Adaptor with arguments _Args.
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/100577.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/100577.cc
index 8ef084621f9..4040f474ad9 100644
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/100577.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/100577.cc
@@ -21,6 +21,7 @@
 // PR libstdc++/100577
 
 #include <ranges>
+#include <functional>
 
 namespace ranges = std::ranges;
 namespace views = std::ranges::views;
@@ -113,4 +114,22 @@ test03()
   x | std::views::drop(S{});
 }
 
+void
+test04()
+{
+  // Non-trivially-copyable extra arguments make a closure not simple.
+  using F = std::function<bool(bool)>;
+  static_assert(!std::is_trivially_copyable_v<F>);
+  using views::__adaptor::__adaptor_has_simple_extra_args;
+  using views::__adaptor::__closure_has_simple_call_op;
+  static_assert(!__adaptor_has_simple_extra_args<decltype(views::take_while), F>);
+  static_assert(!__adaptor_has_simple_extra_args<decltype(views::drop_while), F>);
+  static_assert(!__adaptor_has_simple_extra_args<decltype(views::filter), F>);
+  static_assert(!__adaptor_has_simple_extra_args<decltype(views::transform), F>);
+  static_assert(!__closure_has_simple_call_op<decltype(views::take_while(std::declval<F>()))>);
+  static_assert(!__closure_has_simple_call_op<decltype(views::drop_while(std::declval<F>()))>);
+  static_assert(!__closure_has_simple_call_op<decltype(views::filter(std::declval<F>()))>);
+  static_assert(!__closure_has_simple_call_op<decltype(views::transform(std::declval<F>()))>);
+}
+
 // { dg-prune-output "in requirements" }
-- 
2.32.0.93.g670b81a890