On Mon, 2 Feb 2026 at 19:37, Marek Polacek <[email protected]> wrote:
>
> Bootstrapped/regtested on ppc64le-pc-linux-gnu, ok for trunk?
>
> -- >8 --
> [allocator.members] says that allocator::{,de}allocate should be
> constexpr but currently we don't mark them as such. I had to
We do mark std::allocator::allocate and deallocate, the ones you're
changing below are std::__new_allocator::allocate and
std::__new_allocator::deallocate, which should never be used during
constant eval:
include/bits/allocator.h has:
#if __cplusplus > 201703L
[[nodiscard,__gnu__::__always_inline__]]
constexpr _Tp*
allocate(size_t __n)
{
if (std::__is_constant_evaluated())
{
if (__builtin_mul_overflow(__n, sizeof(_Tp), &__n))
std::__throw_bad_array_new_length();
return static_cast<_Tp*>(::operator new(__n));
}
return __allocator_base<_Tp>::allocate(__n, 0);
}
[[__gnu__::__always_inline__]]
constexpr void
deallocate(_Tp* __p, size_t __n)
{
if (std::__is_constant_evaluated())
{
::operator delete(__p);
return;
}
__allocator_base<_Tp>::deallocate(__p, __n);
}
#endif // C++20
and __allocator_base is __new_allocator (for the default configure
flags anyway).
So I'm surprised that the __new_allocator members need fixing. Why
does the reflection code ever end up looking at the __new_allocator
members?
> work around that in the Reflection code, but it would be better to
> clean this up. (I see no allocation_result so I'm not changing that.)
Right, that's not implemented yet.
>
> gcc/cp/ChangeLog:
>
> * constexpr.cc (is_std_allocator): Don't check for __new_allocator.
> (is_std_allocator_allocate): Make static.
> * cp-tree.h (is_std_allocator_allocate): Remove declaration.
> * reflect.cc (check_out_of_consteval_use): Don't call
> is_std_allocator_allocate.
> (check_consteval_only_fn): Likewise.
>
> libstdc++-v3/ChangeLog:
>
> * include/bits/new_allocator.h (__new_allocator::allocate,
> __new_allocator::deallocate): Add missing constexpr.
> ---
> gcc/cp/constexpr.cc | 6 ++----
> gcc/cp/cp-tree.h | 1 -
> gcc/cp/reflect.cc | 9 +++------
> libstdc++-v3/include/bits/new_allocator.h | 4 ++--
> 4 files changed, 7 insertions(+), 13 deletions(-)
>
> diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
> index a31fe6b113a..a5ccd276a88 100644
> --- a/gcc/cp/constexpr.cc
> +++ b/gcc/cp/constexpr.cc
> @@ -3247,14 +3247,12 @@ is_std_class (tree ctx, const char *name)
> bool
> is_std_allocator (tree ctx)
> {
> - return (is_std_class (ctx, "allocator")
> - || (flag_reflection
> - && is_std_class (ctx, "__new_allocator")));
> + return is_std_class (ctx, "allocator");
> }
>
> /* Return true if FNDECL is std::allocator<T>::{,de}allocate. */
>
> -bool
> +static bool
> is_std_allocator_allocate (tree fndecl)
> {
> tree name = DECL_NAME (fndecl);
> diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
> index 59ab4e40430..1045dfd6014 100644
> --- a/gcc/cp/cp-tree.h
> +++ b/gcc/cp/cp-tree.h
> @@ -9259,7 +9259,6 @@ extern bool is_nondependent_static_init_expression
> (tree);
> extern bool is_static_init_expression (tree);
> extern bool is_std_class (tree, const char *);
> extern bool is_std_allocator (tree);
> -extern bool is_std_allocator_allocate (tree);
> extern bool potential_rvalue_constant_expression (tree);
> extern bool require_potential_constant_expression (tree);
> extern bool require_constant_expression (tree);
> diff --git a/gcc/cp/reflect.cc b/gcc/cp/reflect.cc
> index 24b8d744810..fe417960acf 100644
> --- a/gcc/cp/reflect.cc
> +++ b/gcc/cp/reflect.cc
> @@ -8154,11 +8154,9 @@ check_out_of_consteval_use (tree expr, bool
> complain/*=true*/)
> if (!consteval_only_p (t))
> return NULL_TREE;
>
> + /* Already escalated? */
> if (current_function_decl
> - /* Already escalated. */
> - && (DECL_IMMEDIATE_FUNCTION_P (current_function_decl)
> - /* These functions are magic. */
> - || is_std_allocator_allocate (current_function_decl)))
> + && DECL_IMMEDIATE_FUNCTION_P (current_function_decl))
> {
> *walk_subtrees = false;
> return NULL_TREE;
> @@ -8305,8 +8303,7 @@ check_consteval_only_fn (tree decl)
> if (!DECL_IMMEDIATE_FUNCTION_P (decl)
> && consteval_only_p (decl)
> /* But if the function can be escalated, merrily we roll along. */
> - && !immediate_escalating_function_p (decl)
> - && !is_std_allocator_allocate (decl))
> + && !immediate_escalating_function_p (decl))
> error_at (DECL_SOURCE_LOCATION (decl),
> "function of consteval-only type must be declared %qs",
> "consteval");
> diff --git a/libstdc++-v3/include/bits/new_allocator.h
> b/libstdc++-v3/include/bits/new_allocator.h
> index 5701b8dd254..4fe67f99e5c 100644
> --- a/libstdc++-v3/include/bits/new_allocator.h
> +++ b/libstdc++-v3/include/bits/new_allocator.h
> @@ -122,7 +122,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>
> // NB: __n is permitted to be 0. The C++ standard says nothing
> // about what the return value is when __n == 0.
> - _GLIBCXX_NODISCARD _Tp*
> + _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR _Tp*
> allocate(size_type __n, const void* = static_cast<const void*>(0))
> {
> #if __cplusplus >= 201103L
> @@ -152,7 +152,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> }
>
> // __p is not permitted to be a null pointer.
> - void
> + _GLIBCXX20_CONSTEXPR void
> deallocate(_Tp* __p, size_type __n __attribute__ ((__unused__)))
> {
> #if __cpp_sized_deallocation
>
> base-commit: e02eba0dc7d1aa62c5edf7108e641bcb5c5584b8
> --
> 2.52.0
>
