[clang][bytecode] Check __builtin_memcpy for null pointers (#118313)

Author: tbaederr

clang/lib/AST/ByteCode/InterpBuiltin.cpp

@@ -1796,6 +1796,14 @@ static bool interp__builtin_memcpy(InterpState &S, CodePtr OpPC,
     return true;
   }
 
+  if (SrcPtr.isZero() || DestPtr.isZero()) {
+    Pointer DiagPtr = (SrcPtr.isZero() ? SrcPtr : DestPtr);
+    S.FFDiag(S.Current->getSource(OpPC), diag::note_constexpr_memcpy_null)
+        << /*IsMove=*/false << /*IsWchar=*/false << !SrcPtr.isZero()
+        << DiagPtr.toDiagnosticString(S.getASTContext());
+    return false;
+  }
+
   if (!DoBitCastPtr(S, OpPC, SrcPtr, DestPtr))
     return false;
 

clang/test/AST/ByteCode/builtin-functions.cpp

@@ -1138,4 +1138,12 @@ namespace BuiltinMemcpy {
     return b;
   }
   static_assert(simple() == 12);
+
+
+  extern struct Incomplete incomplete;
+  constexpr struct Incomplete *null_incomplete = 0;
+  static_assert(__builtin_memcpy(null_incomplete, null_incomplete, sizeof(wchar_t))); // both-error {{not an integral constant expression}} \
+                                                                                      // both-note {{source of 'memcpy' is nullptr}}
+
+
 }