From: Patrick Palka <ppalka@redhat.com>
Date: Tue, 18 May 2021 04:26:25 +0000 (-0400)
Subject: libstdc++: Fix condition for memoizing reverse_view::begin() [PR100621]
X-Git-Tag: basepoints/gcc-13~7458
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=03cf8d54e5c27cfe6b184cc96757cab30d8fa1df;p=thirdparty%2Fgcc.git

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 --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 36bccd6b33b9..70794251ec70 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,