[clang] [clang][bytecode] Diagnose regular CK_LValueBitCast cast nodes (PR #175721)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/175721

We already do this similarly for CXXReinterpretCastExprs, except in that case we try harder to make things work.

>From bb4dc96c6193eaa09d226bff61e78af4d6e10eea Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Tue, 13 Jan 2026 08:44:11 +0100
Subject: [PATCH] [clang][bytecode] Diagnose regular CK_LValueBitCast cast
 nodes

We already do this similarly for CXXReinterpretCastExprs, except in that
case we try harder to make things work.
---
 clang/lib/AST/ByteCode/Compiler.cpp | 3 +++
 clang/test/AST/ByteCode/cxx11.cpp   | 4 ++++
 2 files changed, 7 insertions(+)

diff --git a/clang/lib/AST/ByteCode/Compiler.cpp b/clang/lib/AST/ByteCode/Compiler.cpp
index b68576158decc..b39736587034d 100644
--- a/clang/lib/AST/ByteCode/Compiler.cpp
+++ b/clang/lib/AST/ByteCode/Compiler.cpp
@@ -779,6 +779,9 @@ bool Compiler<Emitter>::VisitCastExpr(const CastExpr *CE) {
     // a diagnostic if appropriate.
     return this->delegate(SubExpr);
 
+  case CK_LValueBitCast:
+    return this->emitInvalidCast(CastKind::ReinterpretLike, /*Fatal=*/true, CE);
+
   default:
     return this->emitInvalid(CE);
   }
diff --git a/clang/test/AST/ByteCode/cxx11.cpp b/clang/test/AST/ByteCode/cxx11.cpp
index 9a61321f67a40..e1fb5948b7708 100644
--- a/clang/test/AST/ByteCode/cxx11.cpp
+++ b/clang/test/AST/ByteCode/cxx11.cpp
@@ -33,6 +33,10 @@ constexpr int b = b; // both-error {{must be initialized by a constant expressio
                                                       // both-note {{declared here}}
 
 
+  void func();
+  constexpr int (&fp4)() = (int(&)())func; // both-error {{constant expression}} \
+                                           // both-note {{reinterpret_cast}}
+
 struct S {
   int m;
 };