[clang] [clang][bytecode] Fix a crash in __builtin_object_size() (PR #160519)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/160519

The previous BytOffset computation only makes sense if Ptr points into an array.

>From 766967683f73b6ef9c48f03dd3bb1437a92f4399 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Wed, 24 Sep 2025 15:02:12 +0200
Subject: [PATCH] [clang][bytecode] Fix a crash in __builtin_object_size()

The previous BytOffset computation only makes sense if Ptr points into
an array.
---
 clang/lib/AST/ByteCode/InterpBuiltin.cpp        | 12 ++++++++----
 clang/test/AST/ByteCode/builtin-object-size.cpp |  3 ++-
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/clang/lib/AST/ByteCode/InterpBuiltin.cpp b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
index 5423d3ca73c81..a49992029c742 100644
--- a/clang/lib/AST/ByteCode/InterpBuiltin.cpp
+++ b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
@@ -2449,10 +2449,14 @@ static bool interp__builtin_object_size(InterpState &S, CodePtr OpPC,
     if (Ptr.isBaseClass())
       ByteOffset = computePointerOffset(ASTCtx, Ptr.getBase()) -
                    computePointerOffset(ASTCtx, Ptr);
-    else
-      ByteOffset =
-          computePointerOffset(ASTCtx, Ptr) -
-          computePointerOffset(ASTCtx, Ptr.expand().atIndex(0).narrow());
+    else {
+      if (Ptr.inArray())
+        ByteOffset =
+            computePointerOffset(ASTCtx, Ptr) -
+            computePointerOffset(ASTCtx, Ptr.expand().atIndex(0).narrow());
+      else
+        ByteOffset = 0;
+    }
   } else
     ByteOffset = computePointerOffset(ASTCtx, Ptr);
 
diff --git a/clang/test/AST/ByteCode/builtin-object-size.cpp b/clang/test/AST/ByteCode/builtin-object-size.cpp
index 6f4ef54bcbafa..e4433ea700ccb 100644
--- a/clang/test/AST/ByteCode/builtin-object-size.cpp
+++ b/clang/test/AST/ByteCode/builtin-object-size.cpp
@@ -17,7 +17,8 @@ static_assert(__builtin_object_size(&arrf, 0) == (sizeof(float)*2), "");
 static_assert(__builtin_object_size(&arrf[1], 0) == sizeof(float), "");
 static_assert(__builtin_object_size(&arrf[2], 0) == 0, "");
 
-
+constexpr struct { int a; int b; } F{};
+static_assert(__builtin_object_size(&F.a, 3) == sizeof(int));
 
 struct S {
   int a;