[clang] d2fcb0c - [clang][bytecode] Handle multiple base paths in dynamic_cast (#213592)

[via cfe-commits]

Author: Timm Baeder
Date: 2026-08-03T15:47:10+02:00
New Revision: d2fcb0c9e11f8d8bedc45db0aeba9e0a53141fe5

URL: https://github.com/llvm/llvm-project/commit/d2fcb0c9e11f8d8bedc45db0aeba9e0a53141fe5
DIFF: https://github.com/llvm/llvm-project/commit/d2fcb0c9e11f8d8bedc45db0aeba9e0a53141fe5.diff

LOG: [clang][bytecode] Handle multiple base paths in dynamic_cast (#213592)

This can happen via virtual bases.

Fixes https://github.com/llvm/llvm-project/issues/213569

Added: 
    

Modified: 
    clang/lib/AST/ByteCode/Interp.cpp
    clang/test/AST/ByteCode/dynamic-cast.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/AST/ByteCode/Interp.cpp b/clang/lib/AST/ByteCode/Interp.cpp
index 475d206356de8..5a5a12752dec5 100644
--- a/clang/lib/AST/ByteCode/Interp.cpp
+++ b/clang/lib/AST/ByteCode/Interp.cpp
@@ -2166,9 +2166,13 @@ bool DynamicCast(InterpState &S, CodePtr OpPC, const Type *DestTypePtr,
 
     CXXBasePaths Paths;
     getRecord(P.getBase())->isDerivedFrom(getRecord(P), Paths);
-    assert(std::distance(Paths.begin(), Paths.end()) == 1);
 
-    return Paths.front().Access == AS_private;
+    // Through virtual bases, there might be more than one "direct" base. They
+    // can have 
diff erent access specifiers. They must all be private to be
+    // considered private.
+    return llvm::all_of(Paths, [](const CXXBasePath &P) -> bool {
+      return P.Access == AS_private;
+    });
   };
 
   enum {

diff  --git a/clang/test/AST/ByteCode/dynamic-cast.cpp b/clang/test/AST/ByteCode/dynamic-cast.cpp
index a81bab400a50a..83a745e271a28 100644
--- a/clang/test/AST/ByteCode/dynamic-cast.cpp
+++ b/clang/test/AST/ByteCode/dynamic-cast.cpp
@@ -338,3 +338,17 @@ namespace UnrelatedInitializingPtr {
   constexpr auto p = dynamic_cast<C &>(a); // both-error {{must be initialized by a constant expression}} \
                                            // both-note {{reference dynamic_cast failed: dynamic type 'UnrelatedInitializingPtr::D' of operand does not have a base class of type 'C'}}
 }
+
+namespace VirtualBase {
+  struct A { virtual constexpr ~A() = default; };
+  struct B : public virtual A {};
+  struct C : private virtual A {};
+  struct D : B, C {};
+
+  constexpr bool test() {
+    D d;
+    A *a = static_cast<B *>(&d);
+    return dynamic_cast<C *>(a) == static_cast<C *>(&d);
+  }
+  static_assert(test());
+}