[clang] [clang][bytecode] Diagnose array-to-pointer decays of dummy pointers (PR #106366)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/106366

We have type information for them now, so we can do this.

>From 670598d602949cee9bc8cbfe563563aa699d8505 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Wed, 28 Aug 2024 12:58:29 +0200
Subject: [PATCH] [clang][bytecode] Diagnose array-to-pointer decays of dummy
 pointers

We have type information for them now, so we can do this.
---
 clang/lib/AST/ByteCode/Interp.h    | 2 +-
 clang/test/AST/ByteCode/arrays.cpp | 9 +++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/clang/lib/AST/ByteCode/Interp.h b/clang/lib/AST/ByteCode/Interp.h
index 7ba51f737db491..72f4e8e2764c4e 100644
--- a/clang/lib/AST/ByteCode/Interp.h
+++ b/clang/lib/AST/ByteCode/Interp.h
@@ -2535,7 +2535,7 @@ inline bool ArrayDecay(InterpState &S, CodePtr OpPC) {
   if (!CheckRange(S, OpPC, Ptr, CSK_ArrayToPointer))
     return false;
 
-  if (Ptr.isRoot() || !Ptr.isUnknownSizeArray() || Ptr.isDummy()) {
+  if (Ptr.isRoot() || !Ptr.isUnknownSizeArray()) {
     S.Stk.push<Pointer>(Ptr.atIndex(0));
     return true;
   }
diff --git a/clang/test/AST/ByteCode/arrays.cpp b/clang/test/AST/ByteCode/arrays.cpp
index 47706bedcf3f0c..4097c65f7c6fba 100644
--- a/clang/test/AST/ByteCode/arrays.cpp
+++ b/clang/test/AST/ByteCode/arrays.cpp
@@ -436,6 +436,15 @@ namespace Incomplete {
   constexpr int C = *F.a; // both-error {{must be initialized by a constant expression}} \
                           // both-note {{array-to-pointer decay of array member without known bound}}
 
+  struct X {
+    int a;
+    int b[];
+  };
+  extern X x;
+  constexpr int *xb = x.b; // both-error {{must be initialized by a constant expression}} \
+                           // both-note {{array-to-pointer decay of array member without known bound}}
+
+
   /// These are from test/SemaCXX/constant-expression-cxx11.cpp
   extern int arr[];
   constexpr int *c = &arr[1]; // both-error  {{must be initialized by a constant expression}} \