[committed] libstdc++: Use function object for __decay_copy helper

[committed] libstdc++: Use function object for __decay_copy helper

[Jonathan Wakely]

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By changing __cust_access::__decay_copy from a function template to a
function object we avoid ADL. That means it's fine to call it
unqualified (the compiler won't waste time doing ADL in associated
namespaces, and won't try to complete associated types).

This also makes some other minor simplications to other concepts for the
[range.access] CPOs.

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

libstdc++-v3/ChangeLog:

	* include/bits/iterator_concepts.h (__cust_access::__decay_copy):
	Replace with function object.
	(__cust_access::__member_begin, ___cust_access::_adl_begin): Use
	__decay_copy unqualified.
	* include/bits/ranges_base.h (__member_end, __adl_end):
	Likewise. Use __range_iter_t for type of ranges::begin.
	(__member_rend): Use correct value category for rbegin argument.
	(__member_data): Use __decay_copy unqualified.
	(__begin_data): Use __range_iter_t for type of ranges::begin.

Tested powerpc64le-linux. Committed to trunk.


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commit cb326a6442f09cb36b05ce556fc91e10bfeb0cf6
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Jun 15 14:39:02 2021

    libstdc++: Use function object for __decay_copy helper
    
    By changing __cust_access::__decay_copy from a function template to a
    function object we avoid ADL. That means it's fine to call it
    unqualified (the compiler won't waste time doing ADL in associated
    namespaces, and won't try to complete associated types).
    
    This also makes some other minor simplications to other concepts for the
    [range.access] CPOs.
    
    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/iterator_concepts.h (__cust_access::__decay_copy):
            Replace with function object.
            (__cust_access::__member_begin, ___cust_access::_adl_begin): Use
            __decay_copy unqualified.
            * include/bits/ranges_base.h (__member_end, __adl_end):
            Likewise. Use __range_iter_t for type of ranges::begin.
            (__member_rend): Use correct value category for rbegin argument.
            (__member_data): Use __decay_copy unqualified.
            (__begin_data): Use __range_iter_t for type of ranges::begin.

diff --git a/libstdc++-v3/include/bits/iterator_concepts.h b/libstdc++-v3/include/bits/iterator_concepts.h
index 8723f35c5cb..d18ae32bf20 100644
--- a/libstdc++-v3/include/bits/iterator_concepts.h
+++ b/libstdc++-v3/include/bits/iterator_concepts.h
@@ -930,17 +930,18 @@ namespace ranges
   {
     using std::__detail::__class_or_enum;
 
-    template<typename _Tp>
-      constexpr decay_t<_Tp>
-      __decay_copy(_Tp&& __t)
-      noexcept(is_nothrow_convertible_v<_Tp, decay_t<_Tp>>)
-      { return std::forward<_Tp>(__t); }
+    struct {
+      template<typename _Tp>
+	constexpr decay_t<_Tp>
+	operator()(_Tp&& __t) const
+	noexcept(is_nothrow_convertible_v<_Tp, decay_t<_Tp>>)
+	{ return std::forward<_Tp>(__t); }
+    } inline constexpr __decay_copy{};
 
     template<typename _Tp>
       concept __member_begin = requires(_Tp& __t)
 	{
-	  { __cust_access::__decay_copy(__t.begin()) }
-	    -> input_or_output_iterator;
+	  { __decay_copy(__t.begin()) } -> input_or_output_iterator;
 	};
 
     // Poison pills so that unqualified lookup doesn't find std::begin.
@@ -951,8 +952,7 @@ namespace ranges
       concept __adl_begin = __class_or_enum<remove_reference_t<_Tp>>
 	&& requires(_Tp& __t)
 	{
-	  { __cust_access::__decay_copy(begin(__t)) }
-	    -> input_or_output_iterator;
+	  { __decay_copy(begin(__t)) } -> input_or_output_iterator;
 	};
 
     // Simplified version of std::ranges::begin that only supports lvalues,
diff --git a/libstdc++-v3/include/bits/ranges_base.h b/libstdc++-v3/include/bits/ranges_base.h
index 3bc657ca17e..a63ef8eb7f4 100644
--- a/libstdc++-v3/include/bits/ranges_base.h
+++ b/libstdc++-v3/include/bits/ranges_base.h
@@ -89,6 +89,7 @@ namespace ranges
   namespace __cust_access
   {
     using std::ranges::__detail::__maybe_borrowed_range;
+    using std::__detail::__range_iter_t;
 
     struct _Begin
     {
@@ -127,8 +128,7 @@ namespace ranges
     template<typename _Tp>
       concept __member_end = requires(_Tp& __t)
 	{
-	  { __decay_copy(__t.end()) }
-	    -> sentinel_for<decltype(_Begin{}(std::forward<_Tp>(__t)))>;
+	  { __decay_copy(__t.end()) } -> sentinel_for<__range_iter_t<_Tp>>;
 	};
 
     // Poison pills so that unqualified lookup doesn't find std::end.
@@ -139,8 +139,7 @@ namespace ranges
       concept __adl_end = __class_or_enum<remove_reference_t<_Tp>>
 	&& requires(_Tp& __t)
 	{
-	  { __decay_copy(end(__t)) }
-	    -> sentinel_for<decltype(_Begin{}(std::forward<_Tp>(__t)))>;
+	  { __decay_copy(end(__t)) } -> sentinel_for<__range_iter_t<_Tp>>;
 	};
 
     struct _End
@@ -281,7 +280,7 @@ namespace ranges
       concept __member_rend = requires(_Tp& __t)
 	{
 	  { __decay_copy(__t.rend()) }
-	    -> sentinel_for<decltype(_RBegin{}(__t))>;
+	    -> sentinel_for<decltype(_RBegin{}(std::forward<_Tp>(__t)))>;
 	};
 
     void rend(auto&) = delete;
@@ -507,12 +506,11 @@ namespace ranges
     template<typename _Tp>
       concept __member_data = requires(_Tp& __t)
 	{
-	  { __cust_access::__decay_copy(__t.data()) } -> __pointer_to_object;
+	  { __decay_copy(__t.data()) } -> __pointer_to_object;
 	};
 
     template<typename _Tp>
-      concept __begin_data = requires(_Tp& __t)
-	{ { _Begin{}(__t) } -> contiguous_iterator; };
+      concept __begin_data = contiguous_iterator<__range_iter_t<_Tp>>;
 
     struct _Data
     {

Re: [committed] libstdc++: Use function object for __decay_copy helper

[Jonathan Wakely]

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On Tue, 15 Jun 2021 at 19:28, Jonathan Wakely wrote:
>
> By changing __cust_access::__decay_copy from a function template to a
> function object we avoid ADL. That means it's fine to call it
> unqualified (the compiler won't waste time doing ADL in associated
> namespaces, and won't try to complete associated types).
>
> This also makes some other minor simplications to other concepts for the
> [range.access] CPOs.
>
> Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
>
> libstdc++-v3/ChangeLog:
>
>         * include/bits/iterator_concepts.h (__cust_access::__decay_copy):
>         Replace with function object.
>         (__cust_access::__member_begin, ___cust_access::_adl_begin): Use
>         __decay_copy unqualified.
>         * include/bits/ranges_base.h (__member_end, __adl_end):
>         Likewise. Use __range_iter_t for type of ranges::begin.
>         (__member_rend): Use correct value category for rbegin argument.
>         (__member_data): Use __decay_copy unqualified.
>         (__begin_data): Use __range_iter_t for type of ranges::begin.

That change makes it impossible to import the header in a module.
Fixed by this patch.

Tested powerpc64le-linux. Pushed to trunk.

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commit c25e3bf87975280a603ff18fba387c6707ce4a95
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Jun 16 12:47:32 2021

    libstdc++: Use named struct for __decay_copy
    
    In r12-1486-gcb326a6442f09cb36b05ce556fc91e10bfeb0cf6 I changed
    __decay_copy to be a function object of unnamed class type. This causes
    problems when importing the library headers:
    
    error: conflicting global module declaration 'constexpr const std::ranges::__cust_access::<unnamed struct> std::ranges::__cust_access::__decay_copy'
    
    The fix is to use a named struct instead of an anonymous one.
    
    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/iterator_concepts.h (__decay_copy): Name type.

diff --git a/libstdc++-v3/include/bits/iterator_concepts.h b/libstdc++-v3/include/bits/iterator_concepts.h
index d18ae32bf20..11748e5ed7b 100644
--- a/libstdc++-v3/include/bits/iterator_concepts.h
+++ b/libstdc++-v3/include/bits/iterator_concepts.h
@@ -930,7 +930,8 @@ namespace ranges
   {
     using std::__detail::__class_or_enum;
 
-    struct {
+    struct _Decay_copy final
+    {
       template<typename _Tp>
 	constexpr decay_t<_Tp>
 	operator()(_Tp&& __t) const