Re: [committed] libstdc++: Fix value categories used by ranges access CPOs [PR 100824]

[Jonathan Wakely <jwakely@redhat.com>]

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On 04/06/21 21:46 +0100, Jonathan Wakely wrote:
>On 04/06/21 21:44 +0100, Jonathan Wakely wrote:
>>On 04/06/21 18:03 +0100, Jonathan Wakely wrote:
>>>The implementation of P2091R0 was incomplete, so that some range access
>>>CPOs used perfect forwarding where they should not. This fixes it by
>>>consistently operating on lvalues.
>>>
>>>Some additional changes that are not necessary to fix the bug:
>>>
>>>Modify the __as_const helper to simplify its usage. Instead of deducing
>>>the value category from its argument, and requiring callers to forward
>>>the argument as the correct category, add a non-deduced template
>>>parameter which is used for the value category and accept the argument
>>>as an lvalue. This means callers say __as_const<T>(t) instead of
>>>__as_const(std::forward<T>(t)).
>>>
>>>Always use an lvalue reference type as the template argument for the
>>>_S_noexcept helpers, so that we only instantiate one specialization for
>>>lvalues and rvalues of the same type.
>>>
>>>Move some helper concepts and functions from namespace std::__detail
>>>to ranges::__cust_access, to be consistent with the ranges::begin CPO.
>>>This ensures that the __adl_begin concept and the _Begin::operator()
>>>function are in the same namespace, so unqualified lookup is consistent
>>>and the poison pills for begin are visible to both.
>>>
>>>Simplified static assertions for arrays, because the expression a+0 is
>>>already ill-formed for an array of incomplete type.
>>>
>>>Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
>>>
>>>libstdc++-v3/ChangeLog:
>>>
>>>	PR libstdc++/100824
>>>	* include/bits/iterator_concepts.h (__detail::__decay_copy)
>>>	(__detail::__member_begin, __detail::__adl_begin): Move to
>>>	namespace ranges::__cust_access.
>>>	(__detail::__ranges_begin): Likewise, and rename to __begin.
>>>	Remove redundant static assertion.
>>>	* include/bits/ranges_base.h (_Begin, _End, _RBegin, _REnd):
>>>	Use lvalue in noexcept specifier.
>>>	(__as_const): Add non-deduced parameter for value category.
>>>	(_CBegin, _CEnd, _CRBegin, _CREnd, _CData): Adjust uses of
>>>	__as_const.
>>>	(__member_size, __adl_size, __member_empty, __size0_empty):
>>>	(__eq_iter_empty, __adl_data): Use lvalue objects in
>>>	requirements.
>>>	(__sentinel_size): Likewise. Add check for conversion to
>>>	unsigned-like.
>>>	(__member_data): Allow non-lvalue types to satisfy the concept,
>>>	but use lvalue object in requirements.
>>>	(_Size, _SSize): Remove forwarding to always use an lvalue.
>>>	(_Data): Likewise. Add static assertion for arrays.
>>>	* testsuite/std/ranges/access/cdata.cc: Adjust expected
>>>	behaviour for rvalues. Add negative tests for ill-formed
>>>	expressions.
>>>	* testsuite/std/ranges/access/data.cc: Likewise.
>>>	* testsuite/std/ranges/access/empty.cc: Adjust expected
>>>	behaviour for rvalues.
>>>	* testsuite/std/ranges/access/size.cc: Likewise.
>>
>>An additional problem with ranges::data was pointed out in the PR,
>>fixed with this patch.
>
>And this implements the rest of LWG 3403. The change to the
>ranges::ssize constraints was already done by the first patch in this
>thread, this fixes the return type.

Aaaaand one more fix, as pointed out in the PR.

Tested x86_64-linux. Committed to trunk.

And this one should also be backported to gcc-11 and gcc-10.




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commit 96963713f6a648a0ed890450e02ebdd8ff583b14
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Sat Jun 5 11:42:01 2021

    libstdc++: Fix return type of ranges::ssize for 128-bit integer [PR 100824]
    
    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/100824
            * include/bits/ranges_base.h (_SSize): Return signed type.
            * testsuite/std/ranges/access/ssize.cc: Check with __int128.

diff --git a/libstdc++-v3/include/bits/ranges_base.h b/libstdc++-v3/include/bits/ranges_base.h
index e3c3962bcd9..728d3ad2b25 100644
--- a/libstdc++-v3/include/bits/ranges_base.h
+++ b/libstdc++-v3/include/bits/ranges_base.h
@@ -447,7 +447,7 @@ namespace ranges
 #if defined __STRICT_ANSI__ && defined __SIZEOF_INT128__
 	  // For strict-ansi modes integral<__int128> is false
 	  else if constexpr (__detail::__is_int128<__size_type>)
-	    return static_cast<unsigned __int128>(__size);
+	    return static_cast<__int128>(__size);
 #endif
 	  else // Must be one of __max_diff_type or __max_size_type.
 	    return __detail::__max_diff_type(__size);
diff --git a/libstdc++-v3/testsuite/std/ranges/access/ssize.cc b/libstdc++-v3/testsuite/std/ranges/access/ssize.cc
index f53f462580c..fdbf245d036 100644
--- a/libstdc++-v3/testsuite/std/ranges/access/ssize.cc
+++ b/libstdc++-v3/testsuite/std/ranges/access/ssize.cc
@@ -85,6 +85,20 @@ test06()
   VERIFY( s == 4 );
 }
 
+void
+test07()
+{
+#ifdef __SIZEOF_INT128__
+  struct R
+  {
+    unsigned __int128 size() const { return 4; }
+  };
+  R r;
+  static_assert( std::same_as<decltype(std::ranges::ssize(r)), __int128> );
+  VERIFY( std::ranges::ssize(r) == 4 );
+#endif
+}
+
 int
 main()
 {
@@ -93,4 +107,5 @@ main()
   test04();
   test05();
   test06();
+  test07();
 }