[clang] [clang][bytecode] Fix castBackMemberPointer with null member pointers (PR #223680)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/223680

Do the same thing the current interpreter does: nothing.

>From 699579c0f76d1606f06fd9571151fb9444e330ac Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Tue, 15 Sep 2026 14:46:12 +0200
Subject: [PATCH] [clang][bytecode] Fix castBackMemberPointer with null member
 pointers

Do the same thing the current interpreter does: nothing.
---
 clang/lib/AST/ByteCode/Interp.cpp          | 5 +++++
 clang/test/AST/ByteCode/memberpointers.cpp | 6 ++++++
 2 files changed, 11 insertions(+)

diff --git a/clang/lib/AST/ByteCode/Interp.cpp b/clang/lib/AST/ByteCode/Interp.cpp
index a951827d5d27f..5b0f16abdbf46 100644
--- a/clang/lib/AST/ByteCode/Interp.cpp
+++ b/clang/lib/AST/ByteCode/Interp.cpp
@@ -3203,6 +3203,11 @@ static bool castBackMemberPointer(InterpState &S,
                                   const MemberPointer &MemberPtr,
                                   int32_t BaseOffset,
                                   const RecordDecl *BaseDecl) {
+  if (!MemberPtr.getDecl()) {
+    S.Stk.push<MemberPointer>(MemberPtr);
+    return true;
+  }
+
   const CXXRecordDecl *Expected;
   if (MemberPtr.getPathLength() >= 2)
     Expected = MemberPtr.getPathEntry(MemberPtr.getPathLength() - 2);
diff --git a/clang/test/AST/ByteCode/memberpointers.cpp b/clang/test/AST/ByteCode/memberpointers.cpp
index e2a154914c83b..f077b7ad7ffac 100644
--- a/clang/test/AST/ByteCode/memberpointers.cpp
+++ b/clang/test/AST/ByteCode/memberpointers.cpp
@@ -314,3 +314,9 @@ namespace Errors {
   static_assert(test1(), ""); // both-error {{not an integral constant expression}}
 #endif
 }
+
+namespace NoDecl {
+  struct S {};
+  struct T : S {};
+  void (T::*foo)(void *) = (void (S::*)(void *))(void (T::*)(void *))0;
+}