[clang] 0145ade - [clang][bytecode] Diagnose array-to-pointer-decays on unsized opaque pointers (#226027)

[via cfe-commits]

Author: Timm Baeder
Date: 2026-09-24T13:04:24+02:00
New Revision: 0145ade4fb7c16780a76fb54138974892a941857

URL: https://github.com/llvm/llvm-project/commit/0145ade4fb7c16780a76fb54138974892a941857
DIFF: https://github.com/llvm/llvm-project/commit/0145ade4fb7c16780a76fb54138974892a941857.diff

LOG: [clang][bytecode] Diagnose array-to-pointer-decays on unsized opaque pointers (#226027)

Added: 
    

Modified: 
    clang/lib/AST/ByteCode/Interp.h
    clang/test/AST/ByteCode/invalid.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/AST/ByteCode/Interp.h b/clang/lib/AST/ByteCode/Interp.h
index 14988eb9acb53..a106295022f9b 100644
--- a/clang/lib/AST/ByteCode/Interp.h
+++ b/clang/lib/AST/ByteCode/Interp.h
@@ -3633,10 +3633,19 @@ inline bool ArrayDecay(InterpState &S, CodePtr OpPC) {
       return true;
     }
 
-    if (!Ptr.getType()->isArrayType()) {
+    const OpaquePointer &OP = Ptr.asOpaquePointer();
+    if (!OP.getFieldType()->isArrayType()) {
       S.Stk.push<Pointer>(Ptr);
       return true;
     }
+
+    if (OP.isUnknownSizeArray() && OP.PathLength != 0) {
+      S.FFDiag(S.Current->getSource(OpPC),
+               diag::note_constexpr_unsupported_unsized_array);
+      S.Stk.push<Pointer>(Ptr);
+      return true;
+    }
+
     return arrayElemPtrOpaque(S, OpPC, Ptr,
                               APSInt(APInt::getZero(1), /*IsUnsigned=*/true),
                               /*AllowReplace=*/false);

diff  --git a/clang/test/AST/ByteCode/invalid.cpp b/clang/test/AST/ByteCode/invalid.cpp
index 565d65f60514a..52c91f46ac16d 100644
--- a/clang/test/AST/ByteCode/invalid.cpp
+++ b/clang/test/AST/ByteCode/invalid.cpp
@@ -301,3 +301,15 @@ namespace CompositeFieldInit {
 
   constexpr S2 s2{};
 }
+
+namespace UnsizedArrayAndNonEmptyPath {
+  void foo() {
+    struct S {
+      int m[];
+    } s;
+    constexpr auto p = s.m; // both-error {{must be initialized by a constant expression}} \
+                            // both-note {{array-to-pointer decay of array member without known bound is not supported}}
+  }
+
+  void bar() { foo(); }
+}