[libc++][PMR] Move the pmr::memory_resource destructor into the dylib

[philnik]

Summary

This avoids emitting the VTable of pmr::memory_resource in every TU.

[philnik]

Rebased

[philnik]

Rebased

[ldionne]

I am surprised that we don't need to change the ABI list, can you look into why that's not needed?

I would assume it was already exported by the dylib because it wasn't marked with HIDE_FROM_ABI, but can you confirm that?

[philnik]

Rebased

[philnik]

Rebased; updated ABI list

[philnik]

In D136196#3871517, @ldionne wrote:

I am surprised that we don't need to change the ABI list, can you look into why that's not needed?

I would assume it was already exported by the dylib because it wasn't marked with HIDE_FROM_ABI, but can you confirm that?

The ABI lists actually need updating, the CI just failed before they were checked.

[philnik]

Update changelog

[philnik]

Rebased; Updated all abilists

[EricWF]

Doesn't this need additional availability markup for OS X?

[philnik]

In D136196#3894928, @EricWF wrote:

Doesn't this need additional availability markup for OS X?

It does, but there are some bugs which doesn't allow us to add them currently. See D135813.

[EricWF]

Also, this changes the initialization/atexit behavior of derived memory resource types.

Specifically, because the destructor is no longer defaulted, it's no longer trivial. So the compiler now needs to emit atexit destructors for global memory resources.

I'm not sure this change actually does what we want. I need a minute to test some things.

[EricWF]

So I'm not convinced that we actually emit this vtable. At least not outside of the users control.

Can you provide me with example code that would cause the vtable for this type to be omitted inline?
(without providing a derived class with an inline constructor)

[philnik]

In D136196#3894937, @EricWF wrote:

Also, this changes the initialization/atexit behavior of derived memory resource types.

Specifically, because the destructor is no longer defaulted, it's no longer trivial. So the compiler now needs to emit atexit destructors for global memory resources.

I'm not sure this change actually does what we want. I need a minute to test some things.

Are you sure about that? The class is already non-trivial because it declares virtual functions, and the only difference I can find here is that it doesn't call the destructor of S.

[philnik]

XFAIL tests and update no exceptions abilist

libcxx/include/__memory_resource/memory_resource.h

 #if _LIBCPP_STD_VER > 14
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace pmr {
 
 // [mem.res.class]
 
-_LIBCPP_DIAGNOSTIC_PUSH
-_LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wweak-vtables") // TODO: move destructor into the dylib
 class _LIBCPP_TYPE_VIS _LIBCPP_AVAILABILITY_MEMORY_RESOURCE memory_resource {
   static const size_t __max_align = alignof(max_align_t);
 
 public:
-  virtual ~memory_resource() = default;
+  virtual ~memory_resource();
 
   [[using __gnu__: __returns_nonnull__, __alloc_size__(2), __alloc_align__(3)]] _LIBCPP_HIDE_FROM_ABI void*
   allocate(size_t __bytes, size_t __align = __max_align) {
     return do_allocate(__bytes, __align);
   }
 
   [[__gnu__::__nonnull__]] _LIBCPP_HIDE_FROM_ABI void
   deallocate(void* __p, size_t __bytes, size_t __align = __max_align) {
     do_deallocate(__p, __bytes, __align);
   }
 
   _LIBCPP_HIDE_FROM_ABI bool is_equal(const memory_resource& __other) const noexcept { return do_is_equal(__other); }
 
 private:
   virtual void* do_allocate(size_t, size_t)                       = 0;
   virtual void do_deallocate(void*, size_t, size_t)               = 0;
   virtual bool do_is_equal(memory_resource const&) const noexcept = 0;
 };
-_LIBCPP_DIAGNOSTIC_POP
 
 // [mem.res.eq]
 
 _LIBCPP_AVAILABILITY_MEMORY_RESOURCE inline _LIBCPP_HIDE_FROM_ABI bool
 operator==(const memory_resource& __lhs, const memory_resource& __rhs) noexcept {
   return &__lhs == &__rhs || __lhs.is_equal(__rhs);
 }
 

libcxx/src/memory_resource.cpp

 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace pmr {
 
 // memory_resource
 
-//memory_resource::~memory_resource() {}
+memory_resource::~memory_resource() = default;
 
 // new_delete_resource()
 
 #ifdef _LIBCPP_HAS_NO_ALIGNED_ALLOCATION
 static bool is_aligned_to(void* ptr, size_t align) {
   void* p2     = ptr;
   size_t space = 1;
   void* result = std::align(align, 1, p2, space);