You should be declaring the sizes of all of your variables that being assigned non-constants. That can either be by assigning zeros() of appropriate size to them, or by using coder.varsize() .
Unless you configure for dynamic memory allocation, you should also use an assert() on size() of x to enforce an upper bound on the amount of memory that needs to be allocated on the stack, which is very important when generating for HDL, and can be important when generating for processors with a limited amount of memory. If you are targetting a DSP or 16 bit microcontroller, I would recommend using assert() unless perhaps you can be quite certain that the required amount of memory will be below 1024 bytes.
