[clang] [clang][bytecode] Don't outright reject dyamic casts (PR #167517)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/167517

Just delegate to the subexpr instead.

>From 35b4427346ab8b202adad6d8867dcb697995b94a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Tue, 11 Nov 2025 16:01:46 +0100
Subject: [PATCH] [clang][bytecode] Don't outright reject dyamic casts

Just delegate to the subexpr instead.
---
 clang/lib/AST/ByteCode/Compiler.cpp |  5 +++++
 clang/test/AST/ByteCode/cxx20.cpp   | 10 ++++++++++
 2 files changed, 15 insertions(+)

diff --git a/clang/lib/AST/ByteCode/Compiler.cpp b/clang/lib/AST/ByteCode/Compiler.cpp
index 1243380ca8a6b..dfd99f836d0f8 100644
--- a/clang/lib/AST/ByteCode/Compiler.cpp
+++ b/clang/lib/AST/ByteCode/Compiler.cpp
@@ -773,6 +773,11 @@ bool Compiler<Emitter>::VisitCastExpr(const CastExpr *CE) {
   case CK_ToVoid:
     return discard(SubExpr);
 
+  case CK_Dynamic:
+    // This initially goes through VisitCXXDynamicCastExpr, where we emit
+    // a diagnostic if appropriate.
+    return this->delegate(SubExpr);
+
   default:
     return this->emitInvalid(CE);
   }
diff --git a/clang/test/AST/ByteCode/cxx20.cpp b/clang/test/AST/ByteCode/cxx20.cpp
index cb788fa3e2c07..ea4843e95b01f 100644
--- a/clang/test/AST/ByteCode/cxx20.cpp
+++ b/clang/test/AST/ByteCode/cxx20.cpp
@@ -1201,3 +1201,13 @@ namespace NonPureVirtualCall {
 
   int main() { check(); }
 }
+
+namespace DyamicCast {
+  struct X {
+    virtual constexpr ~X() {}
+  };
+  struct Y : X {};
+  constexpr Y y;
+  constexpr const X *p = &y;
+  constexpr const Y *q = dynamic_cast<const Y*>(p);
+}