[gcc r12-855] libstdc++: Fix condition for memoizing reverse_view::begin() [PR100621]
Patrick Palka
ppalka@gcc.gnu.org
Tue May 18 04:35:16 GMT 2021
https://gcc.gnu.org/g:03cf8d54e5c27cfe6b184cc96757cab30d8fa1df
commit r12-855-g03cf8d54e5c27cfe6b184cc96757cab30d8fa1df
Author: Patrick Palka <ppalka@redhat.com>
Date: Tue May 18 00:26:25 2021 -0400
libstdc++: Fix condition for memoizing reverse_view::begin() [PR100621]
A range being a random access range isn't a sufficient condition for
ranges::next(iter, sent) to have constant time complexity -- it must
also have a sized sentinel. This adjusts the memoization condition for
reverse_view accordingly.
libstdc++-v3/ChangeLog:
PR libstdc++/100621
* include/std/ranges (reverse_view::_S_needs_cached_begin):
Set to true if the underlying non-common random-access range
doesn't have a sized sentinel.
Diff:
---
libstdc++-v3/include/std/ranges | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 36bccd6b33b..70794251ec7 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -3228,7 +3228,9 @@ namespace views::__adaptor
{
private:
static constexpr bool _S_needs_cached_begin
- = !common_range<_Vp> && !random_access_range<_Vp>;
+ = !common_range<_Vp> && !(random_access_range<_Vp>
+ && sized_sentinel_for<sentinel_t<_Vp>,
+ iterator_t<_Vp>>);
[[no_unique_address]]
__detail::__maybe_present_t<_S_needs_cached_begin,
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