On Tue, 02 Jun 2026 at 22:59 +0800, Yuao Ma wrote:
Hi!
This patch makes std::priority_queue constexpr as part of P3372R3. I
am unsure whether I should add the FTM here; since the constexpr
support for std::queue isn't complete yet, I have omitted the FTM from
this patch.
Tested on x86_64-linux. OK for trunk?
Additionally, regarding the implementation strategy for other standard
containers like std::list, it seems inevitable that we will need to
move some function implementations (like _List_node_base) from the .cc
files to the headers. This looks like an ABI break. Is this
acceptable?
Best regards,
Yuao
From c4df4c9bced1407499be8c12438ebf1b7c59fca6 Mon Sep 17 00:00:00 2001
From: Yuao Ma <[email protected]>
Date: Tue, 2 Jun 2026 22:49:19 +0800
Subject: [PATCH] libstdc++: constexpr priority_queue
This patch makes priority_queue constexpr as part of P3372R3.
libstdc++-v3/ChangeLog:
* include/bits/stl_queue.h: Add constexpr.
* testsuite/23_containers/priority_queue/constexpr.cc: New test.
---
libstdc++-v3/include/bits/stl_queue.h | 36 +++++++++++++++-
.../23_containers/priority_queue/constexpr.cc | 43 +++++++++++++++++++
2 files changed, 78 insertions(+), 1 deletion(-)
create mode 100644
libstdc++-v3/testsuite/23_containers/priority_queue/constexpr.cc
diff --git a/libstdc++-v3/include/bits/stl_queue.h
b/libstdc++-v3/include/bits/stl_queue.h
index 5dc846e13e1..d00284277a9 100644
--- a/libstdc++-v3/include/bits/stl_queue.h
+++ b/libstdc++-v3/include/bits/stl_queue.h
@@ -607,28 +607,35 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _Seq = _Sequence, typename _Requires = typename
enable_if<__and_<is_default_constructible<_Compare>,
is_default_constructible<_Seq>>::value>::type>
+ _GLIBCXX26_CONSTEXPR
priority_queue()
: c(), comp() { }
+ _GLIBCXX26_CONSTEXPR
explicit
priority_queue(const _Compare& __x, const _Sequence& __s)
: c(__s), comp(__x)
{ std::make_heap(c.begin(), c.end(), comp); }
+ _GLIBCXX26_CONSTEXPR
explicit
priority_queue(const _Compare& __x, _Sequence&& __s = _Sequence())
: c(std::move(__s)), comp(__x)
{ std::make_heap(c.begin(), c.end(), comp); }
+ _GLIBCXX26_CONSTEXPR
priority_queue(const priority_queue&) = default;
+ _GLIBCXX26_CONSTEXPR
These two changes are not needed. The defaulted special members will
be constexpr by default.
priority_queue& operator=(const priority_queue&) = default;
+ _GLIBCXX26_CONSTEXPR
priority_queue(priority_queue&& __q)
noexcept(__and_<is_nothrow_move_constructible<_Sequence>,
is_nothrow_move_constructible<_Compare>>::value)
: c(std::move(__q.c)), comp(std::move(__q.comp))
{ __q.c.clear(); }
+ _GLIBCXX26_CONSTEXPR
priority_queue&
operator=(priority_queue&& __q)
noexcept(__and_<is_nothrow_move_assignable<_Sequence>,
@@ -641,32 +648,38 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
template<typename _Alloc, typename _Requires = _Uses<_Alloc>>
+ _GLIBCXX26_CONSTEXPR
explicit
priority_queue(const _Alloc& __a)
: c(__a), comp() { }
template<typename _Alloc, typename _Requires = _Uses<_Alloc>>
+ _GLIBCXX26_CONSTEXPR
priority_queue(const _Compare& __x, const _Alloc& __a)
: c(__a), comp(__x) { }
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2537. Constructors [...] taking allocators should call make_heap
template<typename _Alloc, typename _Requires = _Uses<_Alloc>>
+ _GLIBCXX26_CONSTEXPR
priority_queue(const _Compare& __x, const _Sequence& __c,
const _Alloc& __a)
: c(__c, __a), comp(__x)
{ std::make_heap(c.begin(), c.end(), comp); }
template<typename _Alloc, typename _Requires = _Uses<_Alloc>>
+ _GLIBCXX26_CONSTEXPR
priority_queue(const _Compare& __x, _Sequence&& __c, const _Alloc& __a)
: c(std::move(__c), __a), comp(__x)
{ std::make_heap(c.begin(), c.end(), comp); }
template<typename _Alloc, typename _Requires = _Uses<_Alloc>>
+ _GLIBCXX26_CONSTEXPR
priority_queue(const priority_queue& __q, const _Alloc& __a)
: c(__q.c, __a), comp(__q.comp) { }
template<typename _Alloc, typename _Requires = _Uses<_Alloc>>
+ _GLIBCXX26_CONSTEXPR
priority_queue(priority_queue&& __q, const _Alloc& __a)
: c(std::move(__q.c), __a), comp(std::move(__q.comp))
{ __q.c.clear(); }
@@ -704,6 +717,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// 3529. priority_queue(first, last) should construct c with (first, last)
template<typename _InputIterator,
typename = std::_RequireInputIter<_InputIterator>>
+ _GLIBCXX26_CONSTEXPR
priority_queue(_InputIterator __first, _InputIterator __last,
const _Compare& __x = _Compare())
: c(__first, __last), comp(__x)
@@ -713,6 +727,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// 3522. Missing requirement on InputIterator template parameter
template<typename _InputIterator,
typename = std::_RequireInputIter<_InputIterator>>
+ _GLIBCXX26_CONSTEXPR
priority_queue(_InputIterator __first, _InputIterator __last,
const _Compare& __x, const _Sequence& __s)
: c(__s), comp(__x)
@@ -724,6 +739,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _InputIterator,
typename = std::_RequireInputIter<_InputIterator>>
+ _GLIBCXX26_CONSTEXPR
priority_queue(_InputIterator __first, _InputIterator __last,
const _Compare& __x, _Sequence&& __s)
: c(std::move(__s)), comp(__x)
@@ -741,6 +757,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _InputIterator, typename _Alloc,
typename = std::_RequireInputIter<_InputIterator>,
typename _Requires = _Uses<_Alloc>>
+ _GLIBCXX26_CONSTEXPR
priority_queue(_InputIterator __first, _InputIterator __last,
const _Alloc& __alloc)
: c(__first, __last, __alloc), comp()
@@ -749,6 +766,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _InputIterator, typename _Alloc,
typename = std::_RequireInputIter<_InputIterator>,
typename _Requires = _Uses<_Alloc>>
+ _GLIBCXX26_CONSTEXPR
priority_queue(_InputIterator __first, _InputIterator __last,
const _Compare& __x, const _Alloc& __alloc)
: c(__first, __last, __alloc), comp(__x)
@@ -757,6 +775,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _InputIterator, typename _Alloc,
typename = std::_RequireInputIter<_InputIterator>,
typename _Requires = _Uses<_Alloc>>
+ _GLIBCXX26_CONSTEXPR
priority_queue(_InputIterator __first, _InputIterator __last,
const _Compare& __x, const _Sequence& __s,
const _Alloc& __alloc)
@@ -769,6 +788,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _InputIterator, typename _Alloc,
typename _Requires = _Uses<_Alloc>>
+ _GLIBCXX26_CONSTEXPR
priority_queue(_InputIterator __first, _InputIterator __last,
const _Compare& __x, _Sequence&& __s,
const _Alloc& __alloc)
@@ -788,18 +808,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* @{
*/
template<__detail::__container_compatible_range<_Tp> _Rg>
+ _GLIBCXX26_CONSTEXPR
priority_queue(from_range_t, _Rg&& __rg,
const _Compare& __x = _Compare())
: c(ranges::to<_Sequence>(std::forward<_Rg>(__rg))), comp(__x)
{ std::make_heap(c.begin(), c.end(), comp); }
template<__detail::__container_compatible_range<_Tp> _Rg, typename _Alloc>
+ _GLIBCXX26_CONSTEXPR
priority_queue(from_range_t, _Rg&& __rg, const _Compare& __x,
const _Alloc& __a)
: c(ranges::to<_Sequence>(std::forward<_Rg>(__rg), __a)), comp(__x)
{ std::make_heap(c.begin(), c.end(), comp); }
template<__detail::__container_compatible_range<_Tp> _Rg, typename _Alloc>
+ _GLIBCXX26_CONSTEXPR
priority_queue(from_range_t, _Rg&& __rg, const _Alloc& __a)
: c(ranges::to<_Sequence>(std::forward<_Rg>(__rg), __a)), comp()
{ std::make_heap(c.begin(), c.end(), comp); }
@@ -809,12 +832,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
/**
* Returns true if the %queue is empty.
*/
- _GLIBCXX_NODISCARD bool
+ _GLIBCXX_NODISCARD
+ _GLIBCXX26_CONSTEXPR
Please put the two SHOUTING MACROS on the same line.
+ bool
empty() const
{ return c.empty(); }
/** Returns the number of elements in the %queue. */
_GLIBCXX_NODISCARD
+ _GLIBCXX26_CONSTEXPR
Same here.
size_type
size() const
{ return c.size(); }
@@ -824,6 +850,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* element of the %queue.
*/
_GLIBCXX_NODISCARD
+ _GLIBCXX26_CONSTEXPR
And here.
const_reference
top() const
{
@@ -839,6 +866,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* The time complexity of the operation depends on the underlying
* sequence.
*/
+ _GLIBCXX26_CONSTEXPR
void
push(const value_type& __x)
{
@@ -847,6 +875,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
#if __cplusplus >= 201103L
+ _GLIBCXX26_CONSTEXPR
void
push(value_type&& __x)
{
@@ -855,6 +884,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
template<typename... _Args>
+ _GLIBCXX26_CONSTEXPR
void
emplace(_Args&&... __args)
{
@@ -865,6 +895,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#if __glibcxx_containers_ranges // C++ >= 23
template<__detail::__container_compatible_range<_Tp> _Rg>
+ _GLIBCXX26_CONSTEXPR
void
push_range(_Rg&& __rg)
{
@@ -887,6 +918,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* data is needed, it should be retrieved before pop() is
* called.
*/
+ _GLIBCXX26_CONSTEXPR
void
pop()
{
@@ -896,6 +928,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
#if __cplusplus >= 201103L
+ _GLIBCXX26_CONSTEXPR
void
swap(priority_queue& __pq)
noexcept(__and_<
@@ -964,6 +997,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#if __cplusplus >= 201103L
template<typename _Tp, typename _Sequence, typename _Compare>
+ _GLIBCXX26_CONSTEXPR
inline
#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
// Constrained free swap overload, see p0185r1
diff --git a/libstdc++-v3/testsuite/23_containers/priority_queue/constexpr.cc
b/libstdc++-v3/testsuite/23_containers/priority_queue/constexpr.cc
new file mode 100644
index 00000000000..fe85617416d
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/priority_queue/constexpr.cc
@@ -0,0 +1,43 @@
+// { dg-do compile { target c++26 } }
+#include <queue>
+
+constexpr bool test_constexpr_priority_queue() {
+ std::priority_queue<int> pq;
+ if (!pq.empty()) return false;
+ if (pq.size() != 0) return false;
+
+ pq.push(10);
+ if (pq.empty()) return false;
+ if (pq.size() != 1) return false;
+ if (pq.top() != 10) return false;
+
+ pq.emplace(30);
+ pq.emplace(20);
+ if (pq.size() != 3) return false;
+ if (pq.top() != 30) return false;
+
+ pq.pop();
+ if (pq.size() != 2) return false;
+ if (pq.top() != 20) return false;
+
+ std::priority_queue<int> pq2;
+ pq2 = pq;
+ if (pq2.size() != 2) return false;
+ if (pq2.top() != 20) return false;
+
+ std::priority_queue<int> pq3;
+ pq3.push(100);
+ pq.swap(pq3);
+ if (pq.size() != 1 || pq.top() != 100) return false;
+ if (pq3.size() != 2 || pq3.top() != 20) return false;
+
+ int arr[] = {50, 200, 10};
+ pq.push_range(arr);
+ if (pq.size() != 4) return false;
+ if (pq.top() != 200) return false;
+
+ return true;
+}
+
+static_assert(test_constexpr_priority_queue(),
+ "constexpr priority_queue test failed!");
--
2.53.0
