[libcxx] Use alias for detecting overriden function (#120805)

This mechanism is preferable in environments like embedded since it
doesn't require special handling of the custom section.

This is a reland of https://github.com/llvm/llvm-project/pull/114961
which addresses the issue reported by downstream users. Specifically,
the two differences from the previous version are:

* The internal `symbol##_impl__` symbol in the Mach-O implementation is
  annotated with `__attribute__((used))` to prevent LTO from deleting it
  which we've seen in the previous version.
* `__is_function_overridden` is marked as `inline` so these symbols are
  placed in a COMDAT (or fully inlined) to avoid duplicate symbol errors
  which we've seen in the previous version.

1 files changed, 10 insertions, 12 deletions

diff --git a/libcxxabi/src/stdlib_new_delete.cpp b/libcxxabi/src/stdlib_new_delete.cpp
index f386b28f0cfe..73798e211c31 100644
--- a/libcxxabi/src/stdlib_new_delete.cpp
+++ b/libcxxabi/src/stdlib_new_delete.cpp
@@ -63,7 +63,7 @@ static void* operator_new_impl(std::size_t size) {
   return p;
 }
 
-_LIBCPP_MAKE_OVERRIDABLE_FUNCTION_DETECTABLE _LIBCPP_WEAK void* operator new(std::size_t size) _THROW_BAD_ALLOC {
+_LIBCPP_OVERRIDABLE_FUNCTION(_Znwm, void*, operator new, (std::size_t size)) _THROW_BAD_ALLOC {
   void* p = operator_new_impl(size);
   if (p == nullptr)
     __throw_bad_alloc_shim();
@@ -74,7 +74,7 @@ _LIBCPP_WEAK void* operator new(size_t size, const std::nothrow_t&) noexcept {
 #if !_LIBCPP_HAS_EXCEPTIONS
 #  if _LIBCPP_CAN_DETECT_OVERRIDDEN_FUNCTION
   _LIBCPP_ASSERT_SHIM(
-      !std::__is_function_overridden(static_cast<void* (*)(std::size_t)>(&operator new)),
+      !std::__is_function_overridden<static_cast<void* (*)(std::size_t)>(&operator new)>(),
       "libc++ was configured with exceptions disabled and `operator new(size_t)` has been overridden, "
       "but `operator new(size_t, nothrow_t)` has not been overridden. This is problematic because "
       "`operator new(size_t, nothrow_t)` must call `operator new(size_t)`, which will terminate in case "
@@ -94,7 +94,7 @@ _LIBCPP_WEAK void* operator new(size_t size, const std::nothrow_t&) noexcept {
 #endif
 }
 
-_LIBCPP_MAKE_OVERRIDABLE_FUNCTION_DETECTABLE _LIBCPP_WEAK void* operator new[](size_t size) _THROW_BAD_ALLOC {
+_LIBCPP_OVERRIDABLE_FUNCTION(_Znam, void*, operator new[], (size_t size)) _THROW_BAD_ALLOC {
   return ::operator new(size);
 }
 
@@ -102,7 +102,7 @@ _LIBCPP_WEAK void* operator new[](size_t size, const std::nothrow_t&) noexcept {
 #if !_LIBCPP_HAS_EXCEPTIONS
 #  if _LIBCPP_CAN_DETECT_OVERRIDDEN_FUNCTION
   _LIBCPP_ASSERT_SHIM(
-      !std::__is_function_overridden(static_cast<void* (*)(std::size_t)>(&operator new[])),
+      !std::__is_function_overridden<static_cast<void* (*)(std::size_t)>(&operator new[])>(),
       "libc++ was configured with exceptions disabled and `operator new[](size_t)` has been overridden, "
       "but `operator new[](size_t, nothrow_t)` has not been overridden. This is problematic because "
       "`operator new[](size_t, nothrow_t)` must call `operator new[](size_t)`, which will terminate in case "
@@ -156,8 +156,8 @@ static void* operator_new_aligned_impl(std::size_t size, std::align_val_t alignm
   return p;
 }
 
-_LIBCPP_MAKE_OVERRIDABLE_FUNCTION_DETECTABLE _LIBCPP_WEAK void*
-operator new(std::size_t size, std::align_val_t alignment) _THROW_BAD_ALLOC {
+_LIBCPP_OVERRIDABLE_FUNCTION(_ZnwmSt11align_val_t, void*, operator new, (std::size_t size, std::align_val_t alignment))
+_THROW_BAD_ALLOC {
   void* p = operator_new_aligned_impl(size, alignment);
   if (p == nullptr)
     __throw_bad_alloc_shim();
@@ -168,7 +168,7 @@ _LIBCPP_WEAK void* operator new(size_t size, std::align_val_t alignment, const s
 #  if !_LIBCPP_HAS_EXCEPTIONS
 #    if _LIBCPP_CAN_DETECT_OVERRIDDEN_FUNCTION
   _LIBCPP_ASSERT_SHIM(
-      !std::__is_function_overridden(static_cast<void* (*)(std::size_t, std::align_val_t)>(&operator new)),
+      !std::__is_function_overridden<static_cast<void* (*)(std::size_t, std::align_val_t)>(&operator new)>(),
       "libc++ was configured with exceptions disabled and `operator new(size_t, align_val_t)` has been overridden, "
       "but `operator new(size_t, align_val_t, nothrow_t)` has not been overridden. This is problematic because "
       "`operator new(size_t, align_val_t, nothrow_t)` must call `operator new(size_t, align_val_t)`, which will "
@@ -188,16 +188,14 @@ _LIBCPP_WEAK void* operator new(size_t size, std::align_val_t alignment, const s
 #  endif
 }
 
-_LIBCPP_MAKE_OVERRIDABLE_FUNCTION_DETECTABLE _LIBCPP_WEAK void*
-operator new[](size_t size, std::align_val_t alignment) _THROW_BAD_ALLOC {
-  return ::operator new(size, alignment);
-}
+_LIBCPP_OVERRIDABLE_FUNCTION(_ZnamSt11align_val_t, void*, operator new[], (size_t size, std::align_val_t alignment))
+_THROW_BAD_ALLOC { return ::operator new(size, alignment); }
 
 _LIBCPP_WEAK void* operator new[](size_t size, std::align_val_t alignment, const std::nothrow_t&) noexcept {
 #  if !_LIBCPP_HAS_EXCEPTIONS
 #    if _LIBCPP_CAN_DETECT_OVERRIDDEN_FUNCTION
   _LIBCPP_ASSERT_SHIM(
-      !std::__is_function_overridden(static_cast<void* (*)(std::size_t, std::align_val_t)>(&operator new[])),
+      !std::__is_function_overridden<static_cast<void* (*)(std::size_t, std::align_val_t)>(&operator new[])>(),
       "libc++ was configured with exceptions disabled and `operator new[](size_t, align_val_t)` has been overridden, "
       "but `operator new[](size_t, align_val_t, nothrow_t)` has not been overridden. This is problematic because "
       "`operator new[](size_t, align_val_t, nothrow_t)` must call `operator new[](size_t, align_val_t)`, which will "