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* [gcc r12-1567] libstdc++: Non-triv-copyable extra args aren't simple [PR100940]
@ 2021-06-17 13:46 Patrick Palka
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From: Patrick Palka @ 2021-06-17 13:46 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:2b87f3318cf6334a3a42dcf27f2fdec0fce04665
commit r12-1567-g2b87f3318cf6334a3a42dcf27f2fdec0fce04665
Author: Patrick Palka <ppalka@redhat.com>
Date: Thu Jun 17 09:46:07 2021 -0400
libstdc++: Non-triv-copyable extra args aren't simple [PR100940]
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.
PR libstdc++/100940
libstdc++-v3/ChangeLog:
* include/std/ranges (__adaptor::_Partial): For the "simple"
forwarding partial specializations, also require that
the extra arguments are trivially copyable.
* testsuite/std/ranges/adaptors/100577.cc (test04): New test.
Diff:
---
libstdc++-v3/include/std/ranges | 8 +++++---
libstdc++-v3/testsuite/std/ranges/adaptors/100577.cc | 14 ++++++++++++++
2 files changed, 19 insertions(+), 3 deletions(-)
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index a4289009bc4..73c35dafd29 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -896,11 +896,12 @@ namespace views::__adaptor
};
// Partial specialization of the primary template for the case where the extra
- // arguments of the adaptor can always be safely forwarded by const reference.
- // This lets us get away with a single operator() overload, which makes
- // overload resolution failure diagnostics more concise.
+ // arguments of the adaptor can always be safely and efficiently forwarded by
+ // const reference. This lets us get away with a single operator() overload,
+ // which makes overload resolution failure diagnostics more concise.
template<typename _Adaptor, typename... _Args>
requires __adaptor_has_simple_extra_args<_Adaptor, _Args...>
+ && (is_trivially_copyable_v<_Args> && ...)
struct _Partial<_Adaptor, _Args...> : _RangeAdaptorClosure
{
tuple<_Args...> _M_args;
@@ -930,6 +931,7 @@ namespace views::__adaptor
// where _Adaptor accepts a single extra argument.
template<typename _Adaptor, typename _Arg>
requires __adaptor_has_simple_extra_args<_Adaptor, _Arg>
+ && is_trivially_copyable_v<_Arg>
struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure
{
_Arg _M_arg;
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/100577.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/100577.cc
index 8ef084621f9..06be4980ddb 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 +114,17 @@ 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::__closure_has_simple_call_op;
+ 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" }
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