libstdc++: Make ref_view<R> statically sized if R has static size

This patch introduces ranges::__static_size<_Range> helper functions,
that returns ranges::size(__rg) for __statically_sized_range.
This function is then used for ref_view<R>::size if R has static size,
avoiding dereference of pointer value that is not known at compile time.
Similarly for ref_view<R>::empty() we compare the size with zero, if it
is known statically.

This implements relevant part of P3928R0: static_sized_range by
Hewill Kang. As standard does not specify when constexpr functions
are usable at compile time, such implementation are allowed (but not
mandated) by current draft.

libstdc++-v3/ChangeLog:

	* include/bits/ranges_base.h (ranges::__static_size): Define.
	* include/std/ranges (ref_view::size()): For ranges with static
	size return ranges::__static_size<_Range>.
	(ref_view::empty): For ranges with static size, compare size
	against zero.
	* testsuite/23_containers/inplace_vector/cons/from_iota_neg.cc:
	Expect errors from ref_view uses.
	* testsuite/23_containers/inplace_vector/cons/from_range_neg.cc:
	Expect errors from ref_view uses.

Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Reviewed-by: Patrick Palka <ppalka@redhat.com>
Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>

diff --git a/libstdc++-v3/include/bits/ranges_base.h b/libstdc++-v3/include/bits/ranges_base.h
index fea4100eb09e20c7aa89731b1b3484451b7dc87b..ce1c40fc17f66368dd0d9ba922a8154d1a89a91f 100644 (file)
--- a/libstdc++-v3/include/bits/ranges_base.h
+++ b/libstdc++-v3/include/bits/ranges_base.h
@@ -562,6 +562,20 @@ namespace ranges
   template<typename _Tp>
     concept __static_sized_range = sized_range<_Tp> && requires (_Tp& __t)
       { static_cast<char(*)[size_t(ranges::size(__t) >= 0)]>(nullptr); };
+
+  template<__static_sized_range _Range>
+    consteval range_size_t<_Range>
+    __static_size()
+    {
+      auto __conjure = [](_Range& __r)
+      {
+       if constexpr (ranges::size(__r) <= size_t(-1))
+         return integral_constant<size_t, size_t(ranges::size(__r))>{};
+       else
+         return integral_constant<range_size_t<_Range>, ranges::size(__r)>{};
+      };
+      return range_size_t<_Range>(decltype(__conjure(std::declval<_Range&>()))::value);
+    }
 #endif // C++26
 
   template<typename _Derived>

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 7d8b37f8c5cfbeca83b02c192de6c94fd4c6af05..2f11cc2336f7d0fbfd9678574a67fc3a4a567028 100644 (file)
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -1382,11 +1382,25 @@ namespace views::__adaptor
 
       constexpr bool
       empty() const requires requires { ranges::empty(*_M_r); }
-      { return ranges::empty(*_M_r); }
+      {
+#if __cplusplus > 202302L
+       if constexpr (__static_sized_range<_Range>)
+         return ranges::__static_size<_Range>() == 0;
+       else
+#endif
+         return ranges::empty(*_M_r);
+      }
 
       constexpr auto
       size() const requires sized_range<_Range>
-      { return ranges::size(*_M_r); }
+      {
+#if __cplusplus > 202302L
+       if constexpr (__static_sized_range<_Range>)
+         return ranges::__static_size<_Range>();
+       else
+#endif
+         return ranges::size(*_M_r);
+      }
 
       constexpr auto
       data() const requires contiguous_range<_Range>

diff --git a/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_iota_neg.cc b/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_iota_neg.cc
index ae0b96175b7d76b316fb7df970cbf47a81c27439..6b66b5d97ed9c097e49109147a3e41ed5ef9960b 100644 (file)
--- a/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_iota_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_iota_neg.cc
@@ -33,14 +33,12 @@ test_all()
   std::inplace_vector<int, 15> tr1(std::from_range, ref_view(m12));
 
   std::inplace_vector<int, 10> tm2(std::from_range, m12); // { dg-error "(from here|expansion of)" }
-  // ref_view is not statically sized due pointer dereference
-  std::inplace_vector<int, 10> tr2(std::from_range, ref_view(m12));
+  std::inplace_vector<int, 10> tr2(std::from_range, ref_view(m12)); // { dg-error "(from here|expansion of)" }
 
   StaticIota<__int128, 0> mm;
 
   std::inplace_vector<int, 10> tm3(std::from_range, mm); // { dg-error "(from here|expansion of)" }
-  // ref_view is not statically sized due pointer dereference
-  std::inplace_vector<int, 10> tr3(std::from_range, ref_view(mm));
+  std::inplace_vector<int, 10> tr3(std::from_range, ref_view(mm)); // { dg-error "(from here|expansion of)" }
 }
 
 // { dg-error "static assertion failed" "" { target *-*-* } 0 }

diff --git a/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_range_neg.cc b/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_range_neg.cc
index 48d5b4c56f598da9e581f11f74426afb4602339a..ea187761e5e7a182748ac09e0697c4c0f2de9c15 100644 (file)
--- a/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_range_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_range_neg.cc
@@ -62,16 +62,14 @@ test_all()
 
   test_one(a1); // { dg-error "from here" }
   test_one(s1); // { dg-error "from here" }
-  // ref_view is not statically sized due pointer dereference
-  test_one(ref_view(a1));
-  test_one(a5 | std::views::adjacent<7> | std::views::elements<0>);
+  test_one(ref_view(a1)); // { dg-error "from here" }
+  test_one(a5 | std::views::adjacent<5> | std::views::elements<0>); // { dg-error "from here" }
   test_one(s5 | std::views::adjacent<5> | std::views::elements<0>); // { dg-error "from here" }
 
   test_five(a5); // { dg-error "from here" }
   test_five(s5); // { dg-error "from here" }
-  // ref_view is not statically sized due pointer dereference
-  test_five(ref_view(a5));
-  test_five(a7 | std::views::adjacent<3> | std::views::elements<0>);
+  test_five(ref_view(a5)); // { dg-error "from here" }
+  test_five(a7 | std::views::adjacent<3> | std::views::elements<0>); // { dg-error "from here" }
   test_five(s7 | std::views::adjacent<3> | std::views::elements<0>); // { dg-error "from here" }
 }