[libc++][NFC] Reduce use of __add_lvalue_reference_t

[frederick-vs-ja]

Currently, the occurrences of __add_lvalue_reference_t in __split_buffer and __assoc_state are probably meaningless.

• In __split_buffer, the __alloc_ref and __alloc_const_ref member typedefs are no longer used.
• In __assoc_state, we should simply use _Rp&, which must be well-formed since it's already required that sizeof(_Rp) is well-formed.

This PR removes the meaningless usages. The remaining occurrences in shared_ptr, unique_ptr, and several type traits are meaningful.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: A. Jiang (frederick-vs-ja)

Changes

Currently, the occurrences of __add_lvalue_reference_t in __split_buffer and __assoc_state are probably meaningless.

• In __split_buffer, the __alloc_ref and __alloc_const_ref member typedefs are no longer used.
• In __assoc_state, we should simply use _Rp&, which must be well-formed since it's already required that sizeof(_Rp) is well-formed.

This PR removes the meaningless usages. The remaining occurences in shared_ptr, unique_ptr, and several type traits are meaningful.

---

Full diff: https://github.com/llvm/llvm-project/pull/112497.diff

2 Files Affected:

• (modified) libcxx/include/__split_buffer (-3)
• (modified) libcxx/include/future (+2-2)

diff --git a/libcxx/include/__split_buffer b/libcxx/include/__split_buffer
index dfe552fbb45893..c4817601039f3b 100644
--- a/libcxx/include/__split_buffer
+++ b/libcxx/include/__split_buffer
@@ -80,9 +80,6 @@ public:
   pointer __end_;
   _LIBCPP_COMPRESSED_PAIR(pointer, __end_cap_, allocator_type, __alloc_);
 
-  using __alloc_ref       = __add_lvalue_reference_t<allocator_type>;
-  using __alloc_const_ref = __add_lvalue_reference_t<allocator_type>;
-
   __split_buffer(const __split_buffer&)            = delete;
   __split_buffer& operator=(const __split_buffer&) = delete;
 
diff --git a/libcxx/include/future b/libcxx/include/future
index dfa373d6593c79..f16f4234c48966 100644
--- a/libcxx/include/future
+++ b/libcxx/include/future
@@ -594,7 +594,7 @@ public:
   _LIBCPP_HIDE_FROM_ABI void set_value_at_thread_exit(_Arg&& __arg);
 
   _LIBCPP_HIDE_FROM_ABI _Rp move();
-  _LIBCPP_HIDE_FROM_ABI __add_lvalue_reference_t<_Rp> copy();
+  _LIBCPP_HIDE_FROM_ABI _Rp& copy();
 };
 
 template <class _Rp>
@@ -636,7 +636,7 @@ _Rp __assoc_state<_Rp>::move() {
 }
 
 template <class _Rp>
-__add_lvalue_reference_t<_Rp> __assoc_state<_Rp>::copy() {
+_Rp& __assoc_state<_Rp>::copy() {
   unique_lock<mutex> __lk(this->__mut_);
   this->__sub_wait(__lk);
   if (this->__exception_ != nullptr)

[philnik777]

Thanks for the cleanup!