[libcxx-commits] [libcxxabi] [libc++abi][NFC] Avoid out parameter in dyn_cast_get_derived_info (PR #207326)

[via libcxx-commits]

llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxxabi

Author: Nikolas Klauser (philnik777)

<details>
<summary>Changes</summary>

Returning the object is much more idiomatic than having an out parameter.


---
Full diff: https://github.com/llvm/llvm-project/pull/207326.diff


1 Files Affected:

- (modified) libcxxabi/src/private_typeinfo.cpp (+18-20) 


``````````diff
diff --git a/libcxxabi/src/private_typeinfo.cpp b/libcxxabi/src/private_typeinfo.cpp
index d185f2618a7ea..ba3da519238b7 100644
--- a/libcxxabi/src/private_typeinfo.cpp
+++ b/libcxxabi/src/private_typeinfo.cpp
@@ -99,28 +99,27 @@ struct derived_object_info {
 };
 
 /// A helper function that gets (dynamic_ptr, dynamic_type, offset_to_derived) from static_ptr.
-void dyn_cast_get_derived_info(derived_object_info* info, const void* static_ptr)
-{
+derived_object_info dyn_cast_get_derived_info(const void* static_ptr) {
+  derived_object_info info;
 #if __has_feature(cxx_abi_relative_vtable)
-    // The vtable address will point to the first virtual function, which is 8
-    // bytes after the start of the vtable (4 for the offset from top + 4 for
-    // the typeinfo component).
-    const int32_t* vtable =
-        *reinterpret_cast<const int32_t* const*>(static_ptr);
-    info->offset_to_derived = static_cast<std::ptrdiff_t>(vtable[-2]);
-    info->dynamic_ptr = static_cast<const char*>(static_ptr) + info->offset_to_derived;
-
-    // The typeinfo component is now a relative offset to a proxy.
-    int32_t offset_to_ti_proxy = vtable[-1];
-    const uint8_t* ptr_to_ti_proxy =
-        reinterpret_cast<const uint8_t*>(vtable) + offset_to_ti_proxy;
-    info->dynamic_type = *(reinterpret_cast<const __class_type_info* const*>(ptr_to_ti_proxy));
+  // The vtable address will point to the first virtual function, which is 8
+  // bytes after the start of the vtable (4 for the offset from top + 4 for
+  // the typeinfo component).
+  const int32_t* vtable = *reinterpret_cast<const int32_t* const*>(static_ptr);
+  info.offset_to_derived = static_cast<std::ptrdiff_t>(vtable[-2]);
+  info.dynamic_ptr = static_cast<const char*>(static_ptr) + info.offset_to_derived;
+
+  // The typeinfo component is now a relative offset to a proxy.
+  int32_t offset_to_ti_proxy = vtable[-1];
+  const uint8_t* ptr_to_ti_proxy = reinterpret_cast<const uint8_t*>(vtable) + offset_to_ti_proxy;
+  info.dynamic_type = *(reinterpret_cast<const __class_type_info* const*>(ptr_to_ti_proxy));
 #else
   void** vtable = strip_vtable(*static_cast<void** const*>(static_ptr));
-  info->offset_to_derived = reinterpret_cast<ptrdiff_t>(vtable[-2]);
-  info->dynamic_ptr = static_cast<const char*>(static_ptr) + info->offset_to_derived;
-  info->dynamic_type = static_cast<const __class_type_info*>(vtable[-1]);
+  info.offset_to_derived = reinterpret_cast<ptrdiff_t>(vtable[-2]);
+  info.dynamic_ptr = static_cast<const char*>(static_ptr) + info.offset_to_derived;
+  info.dynamic_type = static_cast<const __class_type_info*>(vtable[-1]);
 #endif
+  return info;
 }
 
 /// A helper function for __dynamic_cast that casts a base sub-object pointer
@@ -915,8 +914,7 @@ __dynamic_cast(const void *static_ptr, const __class_type_info *static_type,
                const __class_type_info *dst_type,
                std::ptrdiff_t src2dst_offset) {
     // Get (dynamic_ptr, dynamic_type) from static_ptr
-    derived_object_info derived_info;
-    dyn_cast_get_derived_info(&derived_info, static_ptr);
+    derived_object_info derived_info = dyn_cast_get_derived_info(static_ptr);
 
     // Initialize answer to nullptr.  This will be changed from the search
     //    results if a non-null answer is found.  Regardless, this is what will

``````````

</details>


https://github.com/llvm/llvm-project/pull/207326