[clang] [clang][bytecode] Don't deref() non-dereferencable pointers (PR #200774)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/200774

That shouldn't happen and the isDummy() check wasn't enough.

>From 3b07a174d38b787aa53d8d3a7bc991aa6c35eae6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Mon, 1 Jun 2026 12:28:25 +0200
Subject: [PATCH] [clang][bytecode] Don't deref() non-dereferencable pointers

That shouldn't happen and the isDummy() check wasn't enough.
---
 clang/lib/AST/ByteCode/Interp.h     |  2 +-
 clang/test/AST/ByteCode/invalid.cpp | 11 +++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/clang/lib/AST/ByteCode/Interp.h b/clang/lib/AST/ByteCode/Interp.h
index 86795e13a14ff..fa77e19afce66 100644
--- a/clang/lib/AST/ByteCode/Interp.h
+++ b/clang/lib/AST/ByteCode/Interp.h
@@ -2599,7 +2599,7 @@ bool SubOffset(InterpState &S, CodePtr OpPC) {
 template <ArithOp Op>
 static inline bool IncDecPtrHelper(InterpState &S, CodePtr OpPC,
                                    const Pointer &Ptr) {
-  if (Ptr.isDummy())
+  if (!Ptr.isDereferencable())
     return false;
 
   using OneT = Char<false>;
diff --git a/clang/test/AST/ByteCode/invalid.cpp b/clang/test/AST/ByteCode/invalid.cpp
index 9513645a74794..fb209d353c4a1 100644
--- a/clang/test/AST/ByteCode/invalid.cpp
+++ b/clang/test/AST/ByteCode/invalid.cpp
@@ -198,3 +198,14 @@ namespace InvalidUnaryOperator {
       ;
   }
 }
+
+namespace IncNonDereferencable {
+  struct S {};
+
+  void foo() {
+    S *s = (foo *)malloc(sizeof(*s)); // both-error {{expected expression}}
+    S *&sref = s;
+    for (int i = 0; i < 2; sref++)
+      ;
+  }
+}