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* [PATCH] libstdc++/ranges: Use perfect forwarding in _Pipe and _Partial ctors
@ 2024-01-10 21:40 Patrick Palka
  2024-01-11 15:28 ` Jonathan Wakely
  0 siblings, 1 reply; 4+ messages in thread
From: Patrick Palka @ 2024-01-10 21:40 UTC (permalink / raw)
  To: gcc-patches; +Cc: libstdc++, Patrick Palka

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

-- >8 --

This avoids redundant moves when composing and partially applying range
adaptor objects.

Note that the new constraints on _Partial's constructor templates are
needed so that it's not inadvertently chosen over the copy constructor
when constructing a _Partial object from a non-const _Partial lvalue.

libstdc++-v3/ChangeLog:

	* include/std/ranges (views::__adaptor::operator|): Perform
	perfect forwarding of arguments.
	(views::__adaptor::_Partial::_Partial): Likewise.
	(views::__adaptor::_Pipe::__Pipe): Likewise.
---
 libstdc++-v3/include/std/ranges | 65 ++++++++++++++++++++-------------
 1 file changed, 39 insertions(+), 26 deletions(-)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 81a857502e3..0734daa42bf 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -957,8 +957,11 @@ namespace views::__adaptor
     requires __is_range_adaptor_closure<_Lhs>
       && __is_range_adaptor_closure<_Rhs>
     constexpr auto
-    operator|(_Lhs __lhs, _Rhs __rhs)
-    { return _Pipe<_Lhs, _Rhs>{std::move(__lhs), std::move(__rhs)}; }
+    operator|(_Lhs&& __lhs, _Rhs&& __rhs)
+    {
+      return _Pipe<decay_t<_Lhs>, decay_t<_Rhs>>{std::forward<_Lhs>(__lhs),
+						 std::forward<_Rhs>(__rhs)};
+    }
 
   // The base class of every range adaptor non-closure.
   //
@@ -1004,10 +1007,12 @@ namespace views::__adaptor
     {
       tuple<_Args...> _M_args;
 
-      constexpr
-      _Partial(_Args... __args)
-	: _M_args(std::move(__args)...)
-      { }
+      template<typename... _Ts>
+	requires (sizeof...(_Ts) == sizeof...(_Args))
+	constexpr
+	_Partial(_Ts&&... __args)
+	  : _M_args(std::forward<_Ts>(__args)...)
+	{ }
 
       // Invoke _Adaptor with arguments __r, _M_args... according to the
       // value category of this _Partial object.
@@ -1046,10 +1051,12 @@ namespace views::__adaptor
     {
       _Arg _M_arg;
 
-      constexpr
-      _Partial(_Arg __arg)
-	: _M_arg(std::move(__arg))
-      { }
+      template<typename _Tp>
+	requires (!same_as<remove_cvref_t<_Tp>, _Partial>)
+	constexpr
+	_Partial(_Tp&& __arg)
+	  : _M_arg(std::forward<_Tp>(__arg))
+	{ }
 
       template<typename _Range>
 	requires __adaptor_invocable<_Adaptor, _Range, const _Arg&>
@@ -1079,10 +1086,12 @@ namespace views::__adaptor
     {
       tuple<_Args...> _M_args;
 
-      constexpr
-      _Partial(_Args... __args)
-	: _M_args(std::move(__args)...)
-      { }
+      template<typename... _Ts>
+	requires (sizeof...(_Ts) == sizeof...(_Args))
+	constexpr
+	_Partial(_Ts&&... __args)
+	  : _M_args(std::forward<_Ts>(__args)...)
+	{ }
 
       // Invoke _Adaptor with arguments __r, const _M_args&... regardless
       // of the value category of this _Partial object.
@@ -1109,10 +1118,12 @@ namespace views::__adaptor
     {
       _Arg _M_arg;
 
-      constexpr
-      _Partial(_Arg __arg)
-	: _M_arg(std::move(__arg))
-      { }
+      template<typename _Tp>
+	requires (!same_as<remove_cvref_t<_Tp>, _Partial>)
+	constexpr
+	_Partial(_Tp&& __arg)
+	  : _M_arg(std::forward<_Tp>(__arg))
+	{ }
 
       template<typename _Range>
 	requires __adaptor_invocable<_Adaptor, _Range, const _Arg&>
@@ -1135,10 +1146,11 @@ namespace views::__adaptor
       [[no_unique_address]] _Lhs _M_lhs;
       [[no_unique_address]] _Rhs _M_rhs;
 
-      constexpr
-      _Pipe(_Lhs __lhs, _Rhs __rhs)
-	: _M_lhs(std::move(__lhs)), _M_rhs(std::move(__rhs))
-      { }
+      template<typename _Tp, typename _Up>
+	constexpr
+	_Pipe(_Tp&& __lhs, _Up&& __rhs)
+	  : _M_lhs(std::forward<_Tp>(__lhs)), _M_rhs(std::forward<_Up>(__rhs))
+	{ }
 
       // Invoke _M_rhs(_M_lhs(__r)) according to the value category of this
       // range adaptor closure object.
@@ -1172,10 +1184,11 @@ namespace views::__adaptor
       [[no_unique_address]] _Lhs _M_lhs;
       [[no_unique_address]] _Rhs _M_rhs;
 
-      constexpr
-      _Pipe(_Lhs __lhs, _Rhs __rhs)
-	: _M_lhs(std::move(__lhs)), _M_rhs(std::move(__rhs))
-      { }
+      template<typename _Tp, typename _Up>
+	constexpr
+	_Pipe(_Tp&& __lhs, _Up&& __rhs)
+	  : _M_lhs(std::forward<_Tp>(__lhs)), _M_rhs(std::forward<_Up>(__rhs))
+	{ }
 
       template<typename _Range>
 	requires __pipe_invocable<const _Lhs&, const _Rhs&, _Range>
-- 
2.43.0.283.ga54a84b333


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2024-01-10 21:40 [PATCH] libstdc++/ranges: Use perfect forwarding in _Pipe and _Partial ctors Patrick Palka
2024-01-11 15:28 ` Jonathan Wakely
2024-01-11 16:11   ` Patrick Palka
2024-01-11 22:56     ` Jonathan Wakely

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