[libcxx-commits] [libcxxabi] [libc++abi][NFC] Return const void* from __dynamic_cast (PR #223737)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxxabi

Author: Nikolas Klauser (philnik777)

<details>
<summary>Changes</summary>

`__dynamic_cast` is only called magically by the compiler, so it really doesn't matter what the exact protoype is as long as it's ABI compatible. Making the return type a `const void*` simplifies the implementation a bit though.


---
Full diff: https://github.com/llvm/llvm-project/pull/223737.diff


1 Files Affected:

- (modified) libcxxabi/src/private_typeinfo.cpp (+7-15) 


``````````diff
diff --git a/libcxxabi/src/private_typeinfo.cpp b/libcxxabi/src/private_typeinfo.cpp
index c94ebad26f3f7..1b74bd28435db 100644
--- a/libcxxabi/src/private_typeinfo.cpp
+++ b/libcxxabi/src/private_typeinfo.cpp
@@ -872,7 +872,7 @@ bool __pointer_to_member_type_info::can_catch_nested(const __shim_type_info* thr
 //    (static_ptr, static_type), then return dynamic_ptr.
 // Else return nullptr.
 
-extern "C" _LIBCXXABI_FUNC_VIS void*
+extern "C" _LIBCXXABI_FUNC_VIS const void*
 __dynamic_cast(const void* static_ptr,
                const __class_type_info* static_type,
                const __class_type_info* dst_type,
@@ -880,28 +880,20 @@ __dynamic_cast(const void* static_ptr,
   // Get (dynamic_ptr, dynamic_type) from 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
-  //    be returned.
-  const void* dst_ptr = 0;
-
   // Find out if we can use a giant short cut in the search
   if (is_equal(derived_info.dynamic_type, dst_type, false)) {
-    dst_ptr = dyn_cast_to_derived(
+    return dyn_cast_to_derived(
         static_ptr, derived_info.dynamic_ptr, static_type, dst_type, derived_info.offset_to_derived, src2dst_offset);
   } else {
     // Optimize toward downcasting: let's first try to do a downcast before
     //   falling back to the slow path.
-    dst_ptr = dyn_cast_try_downcast(
-        static_ptr, derived_info.dynamic_ptr, dst_type, derived_info.dynamic_type, src2dst_offset);
+    if (const void* res = dyn_cast_try_downcast(
+            static_ptr, derived_info.dynamic_ptr, dst_type, derived_info.dynamic_type, src2dst_offset))
+      return res;
 
-    if (!dst_ptr) {
-      dst_ptr = dyn_cast_slow(
-          static_ptr, derived_info.dynamic_ptr, static_type, dst_type, derived_info.dynamic_type, src2dst_offset);
-    }
+    return dyn_cast_slow(
+        static_ptr, derived_info.dynamic_ptr, static_type, dst_type, derived_info.dynamic_type, src2dst_offset);
   }
-
-  return const_cast<void*>(dst_ptr);
 }
 
 #pragma GCC diagnostic pop

``````````

</details>


https://github.com/llvm/llvm-project/pull/223737