On Wed, 11 Dec 2024 at 11:02, Jonathan Wakely <jwak...@redhat.com> wrote:
>
> This was approved in Wrocław as LWG 3900, so that passing an incorrect
> argument intended as an allocator will be ill-formed, instead of
> silently ignored.
>
> This also renames the template parameters and function parameters for
> the allocators, to align with the names in the standard. I found it too
> confusing to have a parameter _Alloc which doesn't correspond to Alloc
> in the standard. Rename _Alloc to _Allocator (which the standard calls
> Allocator) and rename _Na to _Alloc (which the standard calls Alloc).
>
> libstdc++-v3/ChangeLog:
>
> * include/std/generator (_Promise_alloc): Rename template
> parameter. Use __alloc_rebind to rebind allocator.
> (_Promise_alloc::operator new): Replace constraints with a
> static_assert in the body. Rename allocator parameter.
> (_Promise_alloc<void>::_M_allocate): Rename allocator parameter.
> Use __alloc_rebind to rebind allocator.
> (_Promise_alloc<void>::operator new): Rename allocator
> parameter.
> * testsuite/24_iterators/range_generators/alloc.cc: New test.
> * testsuite/24_iterators/range_generators/lwg3900.cc: New test.
> ---
>
> Tested x86_64-linux.
>
> libstdc++-v3/include/std/generator | 55 +++++++++----------
> .../24_iterators/range_generators/alloc.cc | 45 +++++++++++++++
> .../24_iterators/range_generators/lwg3900.cc | 16 ++++++
> 3 files changed, 87 insertions(+), 29 deletions(-)
> create mode 100644
> libstdc++-v3/testsuite/24_iterators/range_generators/alloc.cc
> create mode 100644
> libstdc++-v3/testsuite/24_iterators/range_generators/lwg3900.cc
>
> diff --git a/libstdc++-v3/include/std/generator
> b/libstdc++-v3/include/std/generator
> index 0a14e70064e..16b953e90af 100644
> --- a/libstdc++-v3/include/std/generator
> +++ b/libstdc++-v3/include/std/generator
> @@ -416,13 +416,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> concept _Stateless_alloc =
> (allocator_traits<_All>::is_always_equal::value
> && default_initializable<_All>);
>
> - template<typename _Alloc>
> + template<typename _Allocator>
> class _Promise_alloc
> {
> - using _ATr = allocator_traits<_Alloc>;
> - using _Rebound = typename _ATr::template rebind_alloc<_Alloc_block>;
> - using _Rebound_ATr = typename _ATr
> - ::template rebind_traits<_Alloc_block>;
> + using _Rebound = __alloc_rebind<_Allocator, _Alloc_block>;
> + using _Rebound_ATr = allocator_traits<_Rebound>;
> static_assert(is_pointer_v<typename _Rebound_ATr::pointer>,
> "Must use allocators for true pointers with
> generators");
>
> @@ -465,30 +463,31 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> public:
> void*
> operator new(std::size_t __sz)
> - requires default_initializable<_Rebound> // _Alloc is non-void
> + requires default_initializable<_Rebound> // _Allocator is non-void
> { return _M_allocate({}, __sz); }
>
> - template<typename _Na, typename... _Args>
> + // _GLIBCXX_RESOLVE_LIB_DEFECTS
> + // 3900. The allocator_arg_t overloads of promise_type::operator new
> + // should not be constrained
> + template<typename _Alloc, typename... _Args>
> void*
> operator new(std::size_t __sz,
> - allocator_arg_t, const _Na& __na,
> + allocator_arg_t, const _Alloc& __a,
> const _Args&...)
> - requires convertible_to<const _Na&, _Alloc>
> {
> - return _M_allocate(static_cast<_Rebound>(static_cast<_Alloc>(__na)),
> - __sz);
> + static_assert(convertible_to<const _Alloc&, _Allocator>);
> + return _M_allocate(_Rebound(_Allocator(__a)), __sz);
> }
>
> - template<typename _This, typename _Na, typename... _Args>
> + template<typename _This, typename _Alloc, typename... _Args>
> void*
> operator new(std::size_t __sz,
> const _This&,
> - allocator_arg_t, const _Na& __na,
> + allocator_arg_t, const _Alloc& __a,
> const _Args&...)
> - requires convertible_to<const _Na&, _Alloc>
> {
> - return _M_allocate(static_cast<_Rebound>(static_cast<_Alloc>(__na)),
> - __sz);
> + static_assert(convertible_to<const _Alloc&, _Allocator>);
> + return _M_allocate(_Rebound(_Allocator(__a)), __sz);
> }
>
> void
> @@ -578,20 +577,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> }
> }
>
> - template<typename _Na>
> + template<typename _Alloc>
> static void*
> - _M_allocate(const _Na& __na, std::size_t __csz)
> + _M_allocate(const _Alloc& __a, std::size_t __csz)
> {
> - using _Rebound = typename std::allocator_traits<_Na>
> - ::template rebind_alloc<_Alloc_block>;
> - using _Rebound_ATr = typename std::allocator_traits<_Na>
> - ::template rebind_traits<_Alloc_block>;
> + using _Rebound = __alloc_rebind<_Alloc, _Alloc_block>;
> + using _Rebound_ATr = allocator_traits<_Rebound>;
>
> static_assert(is_pointer_v<typename _Rebound_ATr::pointer>,
> "Must use allocators for true pointers with
> generators");
>
> _Dealloc_fn __d = &_M_deallocator<_Rebound>;
> - auto __b = static_cast<_Rebound>(__na);
> + auto __b = static_cast<_Rebound>(__a);
> auto __asz = _M_alloc_size<_Rebound>(__csz);
> auto __nblk = _Alloc_block::_M_cnt(__asz);
> void* __p = __b.allocate(__nblk);
> @@ -619,20 +616,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> return __p;
> }
>
> - template<typename _Na, typename... _Args>
> + template<typename _Alloc, typename... _Args>
> void*
> operator new(std::size_t __sz,
> - allocator_arg_t, const _Na& __na,
> + allocator_arg_t, const _Alloc& __a,
> const _Args&...)
> - { return _M_allocate(__na, __sz); }
> + { return _M_allocate(__a, __sz); }
>
> - template<typename _This, typename _Na, typename... _Args>
> + template<typename _This, typename _Alloc, typename... _Args>
> void*
> operator new(std::size_t __sz,
> const _This&,
> - allocator_arg_t, const _Na& __na,
> + allocator_arg_t, const _Alloc& __a,
> const _Args&...)
> - { return _M_allocate(__na, __sz); }
> + { return _M_allocate(__a, __sz); }
>
> void
> operator delete(void* __ptr, std::size_t __sz) noexcept
> diff --git a/libstdc++-v3/testsuite/24_iterators/range_generators/alloc.cc
> b/libstdc++-v3/testsuite/24_iterators/range_generators/alloc.cc
> new file mode 100644
> index 00000000000..8671da748dd
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/24_iterators/range_generators/alloc.cc
> @@ -0,0 +1,45 @@
> +// { dg-do run { target c++23 } }
> +
> +#include <generator>
> +#include <testsuite_hooks.h>
> +#include <testsuite_allocator.h>
> +
> +template<typename... Args>
> +std::pmr::generator<int>
> +gen(Args...)
> +{
> + co_yield 1;
> + co_yield 2;
> +}
> +
> +int
> +main()
> +{
> + __gnu_test::memory_resource mr;
> + for (auto _ : gen())
> + VERIFY(mr.number_of_active_allocations() == 0);
> +
> + for (auto _ : gen(std::allocator_arg))
> + VERIFY(mr.number_of_active_allocations() == 0);
> +
> + for (auto _ : gen(std::allocator_arg, std::pmr::new_delete_resource()))
> + VERIFY(mr.number_of_active_allocations() == 0);
> +
> +#if __cpp_exceptions
> + try {
> + for (auto _ : gen(std::allocator_arg, std::pmr::null_memory_resource()))
> + VERIFY(false);
> + } catch (const std::bad_alloc&) {
> + }
> +#endif
> +
> + VERIFY(mr.number_of_active_allocations() == 0);
> +
> + for (auto _ : gen(std::allocator_arg , &mr))
> + VERIFY(mr.number_of_active_allocations() == 1);
> +
> + for (auto _ : gen("const This& argument", std::allocator_arg , &mr))
I have no idea what the promise_type::operator new overload that takes
a const This& argument is for, but this invocation of gen uses it, so
... yay?
> + VERIFY(mr.number_of_active_allocations() == 1);
> +
> + VERIFY(mr.number_of_active_allocations() == 0);
> +}
> diff --git a/libstdc++-v3/testsuite/24_iterators/range_generators/lwg3900.cc
> b/libstdc++-v3/testsuite/24_iterators/range_generators/lwg3900.cc
> new file mode 100644
> index 00000000000..957879e8862
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/24_iterators/range_generators/lwg3900.cc
> @@ -0,0 +1,16 @@
> +// { dg-do compile { target c++23 } }
> +
> +// LWG 3900. allocator_arg_t overloads of generator::promise_type::operator
> new
> +// should not be constrained
> +
> +#include <generator>
> +#include <memory_resource>
> +
> +std::pmr::generator<int>
> +bar(std::allocator_arg_t, std::pmr::memory_resource& mr) // { dg-error
> "here" }
> +{
> + co_yield 3;
> +}
> +
> +// { dg-error "static assertion failed" "" { target *-*-* } 0 }
> +// { dg-error "no matching function .*memory_resource&" "" { target *-*-* }
> 0 }
> --
> 2.47.1
>
