[libcxx-commits] [libcxx] [libc++] Specialize __lazy_synth_three_way_comparator for std::greater and friends (PR #157624)
Nikolas Klauser via libcxx-commits
libcxx-commits at lists.llvm.org
Thu Sep 11 01:35:21 PDT 2025
https://github.com/philnik777 updated https://github.com/llvm/llvm-project/pull/157624
>From 17270f65452b11190589f366792537e533de06b5 Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser at berlin.de>
Date: Tue, 9 Sep 2025 09:50:05 +0200
Subject: [PATCH] [libc++] Specialize __lazy_synth_three_way_comparator for
std::greater and friends
---
.../__utility/lazy_synth_three_way_comparator.h | 17 +++++++++++++++++
.../associative/map/map.ops/find.pass.cpp | 16 ++++++++++++++++
.../multimap/multimap.ops/find.pass.cpp | 13 +++++++++++++
.../associative/multiset/find.pass.cpp | 15 +++++++++++++++
.../containers/associative/set/find.pass.cpp | 15 +++++++++++++++
5 files changed, 76 insertions(+)
diff --git a/libcxx/include/__utility/lazy_synth_three_way_comparator.h b/libcxx/include/__utility/lazy_synth_three_way_comparator.h
index ca98845f04191..635dee1f7e4cb 100644
--- a/libcxx/include/__utility/lazy_synth_three_way_comparator.h
+++ b/libcxx/include/__utility/lazy_synth_three_way_comparator.h
@@ -85,6 +85,23 @@ struct __lazy_synth_three_way_comparator<_Comparator,
}
};
+template <class _Comparator, class _LHS, class _RHS>
+struct __lazy_synth_three_way_comparator<_Comparator,
+ _LHS,
+ _RHS,
+ __enable_if_t<__desugars_to_v<__greater_tag, _Comparator, _LHS, _RHS> &&
+ __has_default_three_way_comparator_v<_LHS, _RHS> > > {
+ // This lifetimebound annotation is technically incorrect, but other specializations actually capture the lifetime of
+ // the comparator.
+ _LIBCPP_HIDE_FROM_ABI __lazy_synth_three_way_comparator(_LIBCPP_CTOR_LIFETIMEBOUND const _Comparator&) {}
+
+ // Same comment as above.
+ _LIBCPP_HIDE_FROM_ABI static __eager_compare_result
+ operator()(_LIBCPP_LIFETIMEBOUND const _LHS& __lhs, _LIBCPP_LIFETIMEBOUND const _RHS& __rhs) {
+ return __eager_compare_result(-__default_three_way_comparator<_LHS, _RHS>()(__lhs, __rhs));
+ }
+};
+
_LIBCPP_END_NAMESPACE_STD
#endif // _LIBCPP___UTILITY_LAZY_SYNTH_THREE_WAY_COMPARATOR_H
diff --git a/libcxx/test/std/containers/associative/map/map.ops/find.pass.cpp b/libcxx/test/std/containers/associative/map/map.ops/find.pass.cpp
index 534d78128407d..79a2e3c202e74 100644
--- a/libcxx/test/std/containers/associative/map/map.ops/find.pass.cpp
+++ b/libcxx/test/std/containers/associative/map/map.ops/find.pass.cpp
@@ -72,6 +72,22 @@ int main(int, char**) {
assert(r == std::next(m.begin(), 8));
}
}
+ { // Check with std::greater to ensure we're actually using the correct comparator
+ using Pair = std::pair<const int, int>;
+ using Map = std::map<int, int, std::greater<int>>;
+ Pair ar[] = {Pair(5, 5), Pair(6, 6), Pair(7, 7), Pair(8, 8), Pair(9, 9), Pair(10, 10), Pair(11, 11), Pair(12, 12)};
+ Map m(ar, ar + sizeof(ar) / sizeof(ar[0]));
+ assert(m.find(12) == std::next(m.begin(), 0));
+ assert(m.find(11) == std::next(m.begin(), 1));
+ assert(m.find(10) == std::next(m.begin(), 2));
+ assert(m.find(9) == std::next(m.begin(), 3));
+ assert(m.find(8) == std::next(m.begin(), 4));
+ assert(m.find(7) == std::next(m.begin(), 5));
+ assert(m.find(6) == std::next(m.begin(), 6));
+ assert(m.find(5) == std::next(m.begin(), 7));
+ assert(m.find(4) == std::next(m.begin(), 8));
+ assert(std::next(m.begin(), 8) == m.end());
+ }
#if TEST_STD_VER >= 11
{
typedef std::pair<const int, double> V;
diff --git a/libcxx/test/std/containers/associative/multimap/multimap.ops/find.pass.cpp b/libcxx/test/std/containers/associative/multimap/multimap.ops/find.pass.cpp
index 15df6c15bfa78..d4cf1bb82b99a 100644
--- a/libcxx/test/std/containers/associative/multimap/multimap.ops/find.pass.cpp
+++ b/libcxx/test/std/containers/associative/multimap/multimap.ops/find.pass.cpp
@@ -69,6 +69,19 @@ int main(int, char**) {
assert(r == m.end());
}
}
+ {
+ using Pair = std::pair<const int, int>;
+ using Map = std::multimap<int, int, std::greater<int>>;
+ Pair arr[] = {
+ Pair(5, 1), Pair(5, 2), Pair(5, 3), Pair(7, 1), Pair(7, 2), Pair(7, 3), Pair(9, 1), Pair(9, 2), Pair(9, 3)};
+ const Map m(arr, arr + sizeof(arr) / sizeof(arr[0]));
+ assert(iter_in_range(std::next(m.begin(), 6), std::next(m.begin(), 9), m.find(5)));
+ assert(m.find(6) == m.end());
+ assert(iter_in_range(std::next(m.begin(), 3), std::next(m.begin(), 6), m.find(7)));
+ assert(m.find(8) == m.end());
+ assert(iter_in_range(std::next(m.begin(), 0), std::next(m.begin(), 3), m.find(9)));
+ assert(m.find(10) == m.end());
+ }
#if TEST_STD_VER >= 11
{
typedef std::multimap<int, double, std::less<int>, min_allocator<std::pair<const int, double>>> M;
diff --git a/libcxx/test/std/containers/associative/multiset/find.pass.cpp b/libcxx/test/std/containers/associative/multiset/find.pass.cpp
index 62e6b9dae431d..95e39b1561b34 100644
--- a/libcxx/test/std/containers/associative/multiset/find.pass.cpp
+++ b/libcxx/test/std/containers/associative/multiset/find.pass.cpp
@@ -71,6 +71,21 @@ int main(int, char**) {
assert(r == std::next(m.begin(), 8));
}
}
+ { // Check with std::greater to ensure we're actually using the correct comparator
+ using Set = std::multiset<int, std::greater<int>>;
+ int ar[] = {5, 6, 7, 8, 9, 10, 11, 12};
+ Set m(ar, ar + sizeof(ar) / sizeof(ar[0]));
+ assert(m.find(12) == std::next(m.begin(), 0));
+ assert(m.find(11) == std::next(m.begin(), 1));
+ assert(m.find(10) == std::next(m.begin(), 2));
+ assert(m.find(9) == std::next(m.begin(), 3));
+ assert(m.find(8) == std::next(m.begin(), 4));
+ assert(m.find(7) == std::next(m.begin(), 5));
+ assert(m.find(6) == std::next(m.begin(), 6));
+ assert(m.find(5) == std::next(m.begin(), 7));
+ assert(m.find(4) == std::next(m.begin(), 8));
+ assert(std::next(m.begin(), 8) == m.end());
+ }
#if TEST_STD_VER >= 11
{
typedef int V;
diff --git a/libcxx/test/std/containers/associative/set/find.pass.cpp b/libcxx/test/std/containers/associative/set/find.pass.cpp
index 88ceff0cb144f..e9573de492e00 100644
--- a/libcxx/test/std/containers/associative/set/find.pass.cpp
+++ b/libcxx/test/std/containers/associative/set/find.pass.cpp
@@ -71,6 +71,21 @@ int main(int, char**) {
assert(r == std::next(m.begin(), 8));
}
}
+ { // Check with std::greater to ensure we're actually using the correct comparator
+ using Set = std::set<int, std::greater<int>>;
+ int ar[] = {5, 6, 7, 8, 9, 10, 11, 12};
+ Set m(ar, ar + sizeof(ar) / sizeof(ar[0]));
+ assert(m.find(12) == std::next(m.begin(), 0));
+ assert(m.find(11) == std::next(m.begin(), 1));
+ assert(m.find(10) == std::next(m.begin(), 2));
+ assert(m.find(9) == std::next(m.begin(), 3));
+ assert(m.find(8) == std::next(m.begin(), 4));
+ assert(m.find(7) == std::next(m.begin(), 5));
+ assert(m.find(6) == std::next(m.begin(), 6));
+ assert(m.find(5) == std::next(m.begin(), 7));
+ assert(m.find(4) == std::next(m.begin(), 8));
+ assert(std::next(m.begin(), 8) == m.end());
+ }
#if TEST_STD_VER >= 11
{
typedef int V;
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