[clang][bytecode] Check for dummy pointers in CopyArray op (#158543)

They can't be written to or read from.

Fixes #158535

Author: tbaederr

clang/lib/AST/ByteCode/Interp.h

@@ -3156,6 +3156,9 @@ inline bool CopyArray(InterpState &S, CodePtr OpPC, uint32_t SrcIndex,
   const auto &SrcPtr = S.Stk.pop<Pointer>();
   const auto &DestPtr = S.Stk.peek<Pointer>();
 
+  if (SrcPtr.isDummy() || DestPtr.isDummy())
+    return false;
+
   for (uint32_t I = 0; I != Size; ++I) {
     const Pointer &SP = SrcPtr.atIndex(SrcIndex + I);
 

clang/test/AST/ByteCode/vectors.cpp

@@ -168,3 +168,15 @@ namespace Assign {
   }
   static_assert(invalid()); // both-error {{not an integral constant expression}}
 }
+
+namespace CopyArrayDummy {
+  struct S {
+    long a, b, c, d;
+  };
+  typedef long T __attribute__((vector_size(4 * sizeof(long))));
+
+  void foo(void) {
+    struct S s;
+    *(T *)&s = (T){0, 1, 2, 3};
+  }
+}